Wednesday, 15 April 2015

Why raw temperatures show too little global warming

In the last few amonths I have written several posts why raw temperature observations may show too little global warming. Let's put it all in perspective.

People who have followed the climate "debate" have probably heard of two potential reasons why raw data shows too much global warming: urbanization and the quality of the siting. These are the two non-climatic changes that mitigation sceptics promote claiming that they are responsible for a large part of the observed warming in the global mean temperature records.

If you only know of biases producing a trend that is artificially too strong, it may come as a surprise that the raw measurements actually have too small a trend and that removing non-climatic changes increases the trend. For example, in the Global Historical Climate Network (GHCNv3) of NOAA, the land temperature change since 1880 is increased by about 0.2°C by the homogenization method that removes non-climatic changes. See figure below.

(If you also consider the adjustments made to ocean temperatures, the net effect of the adjustments is that they make the global temperature increase smaller.)


The global mean temperature estimates from the Global Historical Climate Network (GHCNv3) of NOAA, USA. The red curve shows the global average temperature in the raw data. The blue curve is the global mean temperature after removing non-climatic changes. (Figure by Zeke Hausfather.)

The adjustments are not always that "large". The Berkeley Earth group may much smaller adjustments. The global mean temperature of Berkeley Earth is shown below. However, as noted by Zeke Hausfather in the comments below, also the curve where the method did not explicitly detect breakpoints does homogenize the data partially because it penalises stations that have a very different trend than their neighbours. After removal of non-climatic changes BEST come to a similar climatic trend as seen in GHCNv3.


The global mean temperature estimates from the Berkeley Earth project (previously known as BEST), USA. The blue curve is computed without using their method to detect breakpoints, the red curve the temperature after adjusting for non-climatic changes. (Figure by Steven Mosher.)

Let's go over the reasons why the temperature trend may show too little warming.
Urbanization and siting
Urbanization warms the location of a station, but these stations also tend to move away from the centre to better locations. What matters is where the stations were in the beginning of the observation and where they are now. How much too warm the origin was and how much too warm the ending. This effect has been studied a lot and urban stations seem to have about the same trend as their surrounding (more) rural stations.
 
A recent study for two villages showed that the current location of the weather station is half a degree centigrade cooler than the centre of the village. Many stations started in villages (or cities), thermometers used to be expensive scientific instruments operated by highly educated people and they had to be read daily. Thus the siting of many stations may have improved, which would lead to a cooling bias.
 
When a city station moves to an airport, which happened a lot around WWII, this takes the station (largely) out of the urban heat island. Furthermore, cities are often located near the coast and in valleys. Airports may thus often be located at a higher altitude. Both reasons could lead to a considerable cooling for the fraction of stations that moved to airports.
 
Changes in thermometer screens
During the 20th century the Stevenson screen was established as the dominant thermometer screen. This screen protected the thermometer much better against radiation (solar and heat) than earlier designs. Deficits of earlier measurement methods have artificially warmed the temperatures in the 19th century.
 
Some claim that earlier Stevenson screens were painted with inferior paints. The sun consequently heats up the screen more, which again heats the incoming air. The introduction of modern durable white paints may thus have produced a cooling bias.
 
Currently we are in a transition to Automatic Weather Stations. This can show large changes in either direction for the network they are introduced in. What the net global effect is, is not clear at the moment.
 
Irrigation
Irrigation on average decreases the 2m-temperature by about 1 degree centigrade. At the same time, irrigation has spread enormously during the last century. People preferentially live in irrigated areas and weather stations serve agriculture. Thus it is possible that there is a higher likelihood that weather stations are erected in irrigated areas then elsewhere. In this case irrigation could lead to a spurious cooling trend. For suburban stations an increase of watering gardens could also produce a spurious cooling trend.
It is understandable that in the past the focus was on urbanization as a non-climatic change that could make the warming in the climate records too strong. Then the focus was on whether climate change was happening (detection). To make a strong case, science had to show that even the minimum climatic trend was too large to be due to chance.

Now that we know that the Earth is warming, we no longer just need a minimum estimate of the temperature trend, but the best estimate of the trend. For a realistic assessment of models and impacts we need the best estimate of the trend, not just the minimum possible trend. Thus we need to understand the reasons why raw records may show too little warming and quantify these effects.

Just because the mitigation skeptics are talking nonsense about the temperature record does not mean that there are no real issues with the data and it does not mean that statistical homogenization can remove trend errors sufficiently well. This is a strange blind spot in climate science. As Neville Nicholls, one of the heroes of the homogenization community, writes:
When this work began 25 years or more ago, not even our scientist colleagues were very interested. At the first seminar I presented about our attempts to identify the biases in Australian weather data, one colleague told me I was wasting my time. He reckoned that the raw weather data were sufficiently accurate for any possible use people might make of them.
One wonders how this colleague knew this without studying it.

The reasons for a cooling bias have been studied much too little. At this time we cannot tell which reason is how important. Any of these reasons is potentially important enough to be able to explain the 0.2°C per century trend bias found in GHNv3. Especially in the light of the large range of possible values, a range that we can often not even estimate at the moment. In fact, all the above mentioned reasons could together explain a much larger trend bias, which could dramatically change our assessment of the progress of global warming.

The fact is that we cannot quantify the various cooling biases at the moment and it is a travesty that we can't.


Other posts in this series

Irrigation and paint as reasons for a cooling bias

Temperature trend biases due to urbanization and siting quality changes

Changes in screen design leading to temperature trend biases

Temperature bias from the village heat island

Sunday, 12 April 2015

Flying to the geo science flash mob in Vienna #EGU2015

ICE Train by Rhine River (3619844036)

You get used to it, but actually it is very strange. One week in spring, suddenly over 10 thousand geo scientists turn up in a middle European town, go into a huge building, specially build for such mega flash mobs, talk about arcane topics and find others that want to do the same. Crazy.

Such events also have environmental consequences. Especially travelling to Vienna produces much additional pollution. The UK Tyndall Centre recently produced a report stating that climate scientists should set an example and fly less. Not that this is a large contribution to climate change, but you can claim that for every individual action of a small group. No, the reason is according to the first author Corinne Le Quéré:
“It’s a credibility issue, ... We’re trying to support a change in culture.”
I find the idea very sympathetic, but I could not disagree more.

I do not see less flying making an impact, I do not think it would or should change the credibility of climate scientists and I do not think it supports a culture change.

No impact

Climate change is a [[tragedy of the commons]]. The atmosphere is a resource that every one of us uses; it is overexploited because every individual has benefits from using it and the downsides are spread over everyone. Without coordination these incentives invariably lead to overexploitation. The term tragedy of the commons comes from the communal lands around a village, the commons. Every villager benefits by having too much cattle, all suffer because the land degrades, that is the tragedy. One villager reducing his herd does not solve this problem. The neighbours will just enlarge their herds. You need coordination.

Climate change, the ozone hole or biodiversity loss are extra tough versions of such tragedies of the commons because so many people are involved. That makes coordination difficult. To make the number of participants workable normally nations negotiate to solve these global tragedies.

If half of the population decides to stop eating meat of industrially maltreated animals, that reduces the problem by half. A tragedy of the commons is different. If half of the population stops using fossil fuels, this will at best delay the climate problem a few years and in the worst case also delay the solution by the same time span.

In the end, the solution to global environmental problems will come from social changes. The incentives need to change so that people automatically make other choices and do so because that is the best choice for them too. If climate scientists would act as if climate change is a personal choice problem, rather than a tragedy of the commons, that may give the wrong impression.

Especially for climate change, the preferred behaviour will be even easier once the incentives have changed. Now it may be hard to live without a car where you live, but once the incentives change more people will use public transport and get on their bikes. As a consequence, the quality of public transport will increase and more biking lanes will be build, your office may get showers and the dress code may change. Society needs to change.

Credibility

I do not think that flying less makes climate scientists more credible, nor that it makes a stronger case that climate change is real, nor that people will suddenly realise that 97% of climate scientists agree humans are causing climate change.

Simply put.
If climate scientists fly the mitigation sceptics will call them hypocrites.
If climate scientists do not fly the mitigation sceptics will call them activists.
As always, the best advice is to ignore what the unreasonable say, but it is not a priori clear which option makes climate scientists more credible in the eyes of the public.

There is also nothing special about being a climate scientist, my job is to study the reasons for non-climatic changes in historical observations and to develop algorithms to remove these changes. If I would not be blogging, I would not be thinking often about the economic and human costs of climate change. No more than someone else. I am not suddenly also an expert on all the different impacts of climate change. There might be a few public scientists that have this broad overview, most are simply doing their job and do not have a better idea of the problem as someone reading a decent newspaper.

If people chose to reduce their environmental impact that is great. Some people living like that may also make the transition easier by showing that the behaviour is possible and that you can live a happy life that way. However, anyone who worries about climate change can do that, that is not specific to climatologists.

On credibility. I dare to write this post because I travelled the 880 km to Vienna by train. In doing so only emitted a quarter of the CO2 of a comparable flight, if you believe the calculator of the rail company. I did so because I love going by train, you have more space, you can walk around, see the landscape slowly change. When you fly you have to wait in line all the time and are interrupted continually: get to airport 2 hours in advance, check-in, security, boarding, disembarking, get your luggage, travel to centre. Flying is a waste of your time and it is loud, while travelling by train is a great moment to read books and articles.

Culture change

At the moment we already have the big problem, mainly in the USA, that people who do not like the political solutions claim not to accept the science of climate change. They know so little about the science and about scientists, that we can be sure it is not that the science is lacking or that the scientists are not behaving right. I would see it as a major improvement if these people would no longer come up with specious "arguments" why a science is wrong that they hardly know anything about.

Then we could have an adult conversation and negotiate. The liberals get renewable energy, the conservatives aircraft carriers or whatever they want to have. An interesting way to shift the tax burden to carbon would be to let the US Republicans decide which tax should be lowered the same amount as the carbon tax brings in revenue.

The science and the political solutions are two different things. Someone may hold the opinion that the solutions are worse than the problem. I do not agree, but that is just personal opinion. That is comparing apples and oranges, which is the realm of politics, not science.

This culture does not get better by telling those people that if they accept the science, like 97% of climate scientists, that they should then also take personal consequences and fly less, like 97% of climate scientists.

George Marshall

In a recent TEDx video George Marshall (of Talking Climate) makes a similar case as the Tyndall Centre about personal responsibility. I do not agree with him, but he sure can tell it well and makes many important points. He tells about meeting an expert in marine biodiversity who orders a grilled swordfish, a climate scientist who flies to South America for a summer skying holiday, and about having a conversation with an animal rights activist while Marshall was eating the biggest US hamburger he had ever seen. After which he explains the psychology that enables this disconnect in human minds.





Related reading

Climate Central: Can climate scientists make a difference by not flying?

Tyndall Centre: Towards a culture of low-carbon research for the 21st Century

Also by George Marshall: How to talk to uncle Bob, the climate ostrich

Do dissenters like climate change?

Boomerang effects in science communication: how motivated reasoning and identity cues amplify opinion polarization about climate mitigation policies

Monday, 6 April 2015

Changing your mind


The grave of Isaac Newton. Newton made himself vulnerable, wrote up his mechanics and optics very clearly. So that it could be falsified and was falsified. While he never repented his errors in public on facebook, his erroneous work did science a great service.

Being a scientist is hard. No, not for the mathematics. Being a scientist is nothing for wimps because you have to make yourself vulnerable, write up your ideas so clearly that someone else can show them to be wrong. That is the background of Karl Popper's requirement that scientific hypothesis should be falsifiable.

Being shown to be wrong is not nice. That could be one of the reasons why science is a very recent invention, it does not come to humans easily.

Being shown wrong is central, however, to scientific progress.

Being trivially wrong, of the kind displayed on WUWT every day, does not help science and is very bad for your scientific reputation.

Being wrong in an interesting way is scientific progress. The moment someone shows why you were interestingly wrong, we understand the problem a little better. If you can make your colleagues think and understand things better, that is good. Like Albert Einstein who was wrong about quantum mechanics until he died, but his challenges were interested and enhance his reputation.

Because it is hard to make yourself vulnerable, because it is good for science when you do so, because it is good for science when others show you wrong, the scientific community has a culture that encourages people to be bold and allows them to be wrong in an interesting way. If scientists would receive a hostile fit every time someone shows them wrong, that would not encourage them much to contribute to scientific understanding.

language

It starts with the language. Instead of saying someone was wrong, scientists talk about "progressive insight". Actually, it is a bit more than just language, often scientists really could not have known that they were wrong because some experiment or observation had not been made yet. Often this observation was inspired by their ideas. Often "progressive insight" also an argument that was overlooked and could theoretically have been thought up before. You could call that being wrong, but "progressive insight" is much more helpful.

Such a change of language is apparently also important in eduction. A high school teacher wrote:
One of the biggest challenges is convincing teenagers that they can be wrong about anything, let alone that there's value in it, ... Therefore, a few weeks ago I assigned my 90 or so Freshmen the task of keeping a 9-week Surprise Journal. ...

I've noticed something, well, surprising. In the class culture, acknowledgement that you are mistaken about something has become dubbed a "moment of surprise" (followed by a student scrambling to retrieve their Journal to record it). As this is much more value neutral than "I screwed up," the atmosphere surrounding the topic is less stressful than in previous years (I suspect -- based on anecdotal evidence -- that they have a history of being punished for mistakes and so are justifiably skittish about the whole topic). That by itself makes me inclined to judge this experiment a success, and has already added richness to our subsequent activities and discussions...
[[Nassim Taleb]], who wrote The Black Swan, mentioned that it is easier for Arabs to admit they do not know something, which is much better than pretending you do, because they express this by saying: only God knows. Much more neutral. (It is highly recommended for anyone in the climate "debate" to read one of his books on new and unpredictable risks and human tendencies to be blind to chance.)

This amicable scientific culture is also the reason that scientific articles are clear on the work performed, but very subtle in pointing our problems with previous studies, to the extent that sometimes only an expert can even notice that a previous study was criticized.

A less subtle example of trying to be amicable would be the article that made me "famous". A study comparing the skill of almost all homogenization method used to remove non-climatic changes. In the tables you can find the numbers showing which method performed how well. In the text we only recommended the application of the five best methods and did not write much about the less good ones. The reader is smart enough to make that connection himself.

At conferences I do explicitly state that some methods should better not be used any more. In private conversions I may be even more blunt. I feel this is a good general rule in life: praise people in writing, so that they can read it over and over again, criticize people in person, so that is can be forgotten again and you can judge whether the message had the right impact and is well understood. Easier said than done; the other way around is easier.

The bar between a stupid error and an interesting one goes up during the process. In a brainstorm with your close colleagues, you should be able to mention any idea, a stupid idea may inspire someone else to find a better one. At an internal talk about a new idea, it is okay if some peers or seniors notice the problem. If all peers or too many juniors see the problem, your reputation may suffer.

Similarly, if all people at a workshop see the problem, your reputation takes a hit, but if only one sees it. If someone from another field, who has knowledge that you do not, that should not be a problem; that is what conferences are for, to get feedback from people with other backgrounds. Only few people heard it, it will normally not be sufficiently important to talk about that with people who were not present and the mistake will be quickly forgotten. Like it should, if you want to encourage scientists taking risks.

There is a limit to this amicable culture. Making trivial mistakes hurts your reputation. Making again them after being been shown wrong hurts your reputation even more. Being regularly trivially wrong is where the fun stops. There is no excuse for doing bad science. Quality matters and do not let any mitigation skeptics tell you that they are attacked for the political implications of their work, it is the quality. I am very critical of homogenization and doubt studies on changes in extremes from daily station data, but I have good arguments for it and being skeptical certainly did not hurt me, on the contrary.

The difference between writing text, fixed for eternity, open for critique forever, and spoken language is also the reason why I am not too enthusiastic about tweeting conferences. On the other hand, to reduce travel it would be a nice if the talks of conferences were broadcasted over the internet. To reduce the tension between these two requirements maybe we could make something like [[snapchat]] for scientific talks. You can only look at it once (in the week of the conference) and then the video is deleted forever.

The above is the ideal case. Scientists are also humans. Especially when people keep on making similar wrong claims, when you can no longer speak about mistakes, but really about problems, also scientists can become less friendly. One case where I could understand this well was during a conference about long range dependence. This term is defined in such a vague way that you can not show that a signal does not have it. Thus a colleague asked whether a PhD student working on this had read Karl Popper? His professor answered: "First of all you have to believe in long range dependence."

For scientific progress it is not necessary for scientists to publicly pronounce that the denounce their old work. It is more than sufficient that they reference the new work (which without critique is interpreted as signalling that the reference is worth reading), that they adopt the new ideas, use the new methods and again build on them. The situation is also normally not that clear, scientific progress is a continual "negotiation" process while evidence is gathered. Once the dust settles and the evidence is clear, it would be trivial and silly to ask for a denouncement.



Calls for walks to walks to Canossa only hinder scientific progress.

politics

In politics the situation is different. If politically helpful, the opponent changing his or her mind is put in a bad light and is called flip-flopping. If someone once made a mistake, very unhelpful calls for public retractions, repentance and walks to [[Canossa]] are made. Anything to humiliate the political opponent. Politics does not have to be this way, when I was young politicians in The Netherlands still made an effort to understand and convince each other. A sovereigns we should encourage this and reward it with our votes.

A funny example in the political climate "debate" is that the mitigation skeptic FoxGoose thought the could smear BBD by revealing the BBD had once changed his mind, that BBD was once a mitigation skeptic. He had not counted on the reaction of more scientifically minded people, who praised BBD for his strength to admit having been wrong and to leave the building of lies.
I discovered that I was being lied to. This simply by comparing the “sceptic” narrative with the standard version. Unlike my fellow “sceptics” I was still just barely sceptical enough (though sunk in denial) to check both versions. Once I realised what was going on, that was the end of BBD the lukewarmer (NB: I was never so far gone as to deny the basic physics, only to pretend that S [the climate sensitivity] was very low). All horribly embarrassing now, of course, but you live and learn. Or at least, some of us do. ...

Always check. Fail to do this in business and you will end up bankrupt and in the courts. I failed to check, at least initially, and made a colossal prat out of myself. Oh, and never underestimate the power of denial (aka ‘wishful thinking’). It’s brought down better people than me. ...

There wasn’t a single, defining eureka moment, just a growing sense of unease because nothing seemed to add up. ... Once I eventually started to compare WUWT [Watts Up With That] with RC [RealClimate] and SkS [Skeptical Science], that was it, really.
Mitigation skeptics sometimes state something along the lines: I would believe climate scientists if only they would denounce the hockey stick of Michael Mann as a hoax. Firstly, I simply do not believe this. The mitigation skeptics form a political movement. When mitigation skeptics do not even tell their peers that it is nonsense to deny that the CO2 increases are man made, they signal that politics is more important to them than science. For the worst transgressions at WUWT you will sometimes see people complaining that that will make their movement look bad. Such a strategic argument is probably the strongest argument to make at WUWT, but the right reason to reject nonsense is because it is nonsense.

Secondly, the call to denounce past science also ignores that methods to compute past temperatures have progressed, which is an implicit sign that past methods could naturally be improved. An explicit denouncement would not change the science. To keep on making scientific progress, we should keep the scientific culture of mild indirect criticism alive. The disgusting political attack on science in the USA are part of their cultural wars and should be solved by the Americans. That is not reason to change science. Maybe the Americans could start by simply talking to each other and noticing how much they have in common. Stopping to consume hateful radio, TV and blogs will make the quality your life a lot better.

Let me close with a beautiful analogy by Tom Curtis:
We do not consider the Wright brothers efforts as shoddy because their engines were under powered, their planes flimsy, and their controls rudimentary. To do so would be to forget where they stand in the history of aviation – to apply standards to pioneers that develop on the basis of mature knowledge and experience in the field. Everybody including Michael Mann is certain that, with hindsight, there are things MBH98 could have done better – but we only have that hindsight because they did it first. So, the proper gloss is not “shoddy”, but pioneering.


Related reading

Are debatable scientific questions debatable?
On the difference between scientific disputes and political debates.

Falsifiable and falsification in science
Scientific theories need to be falsifiable. Falsification is not trivial, however, and a perceived discrepancy a reason for further study to get a better understanding, not for a rejection of everything. That is politics.

How climatology treats sceptics
I have been very critical of homogenization. I had good arguments and was royally rewarded for my skepticism. The skeptics that cry persecution may want to have a second look at the quality of their "arguments".

Scientific meetings. The freedom to tweet and the freedom not to be tweeted

Stop all harassment of all scientists now

Climatology is a mature field


* Top photo of Newtons grave from Wikimedia is in the public domain.

Saturday, 4 April 2015

Irrigation and paint as reasons for a cooling bias

Irrigation pump in India 1944

In previous posts on reasons why raw temperature data may show too little global warming I have examined improvements in the siting of stations, improvements in the protection of thermometers against the sun, and moves of urban stations to better locations, in particular to airports. This post will be about the influence of irrigation and watering, as well as improvements in the paints used for thermometer screens.

Irrigation and watering

Irrigation can decrease air temperature by up to 5 degrees and typically decreases the temperature by about 1°C (Cook et al., 2014). Because of irrigation more solar energy is used for evaporation and for transpiration by the plants, rather than for warming of the soil and air.

Over the last century we have seen a large 5 to 6 fold global increase in irrigation; see graph below.



The warming by the Urban Heat Island (UHI) is real. The reason we speak of a possible trend bias due to increases in the UHI is that an urban area has a higher probability of siting a weather station than rural areas. If only for the simple reason that that is where people live and want information on the weather.

The cooling due to increases in irrigation are also real. It seems to be a reasonable assumption that an irrigated area again has a higher probability of siting a weather station. People are more likely to live in irrigated areas and many weather stations are deployed to serve agriculture. While urbanization is a reason for stations to move to better locations, irrigation is no reason for a station to move away. On the contrary maybe even.

The author of the above dataset showing increases in irrigation, Stefan Siebert, writes: "Small irrigation areas are spread across almost all populated areas of the world." You can see this strong relation between irrigation and population on a large scale in the map below. It seems likely that this is also true on local scales.



Many stations are also in suburbs and these are likely watered more than they were in the past when water (energy) was more expensive or people even had to use hand pumps. In the same way as irrigation, watering could produce a cool bias due to more evaporation. Suburbs may thus be even cooler than the surrounding rural areas if there is no irrigation. Does anyone know of any literature about this?

I know of one station in Spain where the ground is watered to comply with WMO guidelines that weather stations should be installed on grass. The surrounding is dry and bare, but the station is lush and green. This could also cause a temperature trend bias under the reasonable assumption that this is a new idea. If anyone knows more about such stations, please let me know.



From whitewash to latex paint

Also the maintenance of the weather station can be important. Over the years better materials and paints may have been used for thermometer screens. If this makes the screens more white, they heat up less and they heat up the air flowing through the Louvres less. More regular cleaning and painting would have the same effect. It is possible that this has improved when climate change made weather services aware that high measurement accuracies are important. Unfortunately, it is also possible that good maintenance is nowadays seen as inefficient.

The mitigation skeptics somehow thought that the effect would go into the other direction. That the bad paints used in the past would be a cooling bias, rather than a warming bias. Something with infra-red albedo. Although most materials used have about the same infra-red albedo and the infra-red radiation fluxes are much smaller than the solar fluxes.

Anthony Watts started a paint experiment in his back garden in July 2007. The first picture below shows three Stevenson screens, a bare one, a screen with modern latex paint and one with whitewash, a chalk paint that quickly fades.



Already 5 months later in December 2007, the whitewash had deteriorated considerably; see below. This should lead to a warm bias for the whitewash screen, especially in summer.

Anthony Watts:
Compare the photo of the whitewash paint screen on 7/13/07 when it was new with one taken today on 12/27/07. No wonder the NWS dumped whitewash as the spec in the 70’s in favor of latex paint. Notice that the Latex painted shelter still looks good today while the Whitewashed shelter is already deteriorating.

In any event the statement of Patrick Michaels “Weather equipment is very high-maintenance. The standard temperature shelter is painted white. If the paint wears or discolors, the shelter absorbs more of the sun’s heat and the thermometer inside will read artificially high.” seems like a realistic statement in light of the photos above.
I have not seen any data from this experiment beyond a plot with one day of temperatures, which was a day one month after the start, showing no clear differences between the Stevenson screens. They were all up to 1°C warmer than the modern ventilated automatic weather station when the sun was shining. (That the most modern ventilated measurement had a cool bias was not emphasized in the article, as you can imagine.) Given that Anthony Watts maintains a stealth political blog against mitigation of climate change, I guess we can conclude that he probably did not like the results, that the old white wash screen was warmer and he did not want to publish that.

We may be able to make a rough estimate the size of the effect by looking at another experiment with a bad screen. In sunny Italy Giuseppina Lopardo and colleagues compared two old aged, yellowed and cracked screens of unventilated automatic weather stations that should have been replaced long ago with a good new screen. The picture to the right shows the screen after 3 years. They found a difference of 0.25°C after 3 years and 0.32°C after 5 years.

The main caveat is that the information on the whitewash comes from Anthony Watts. It may thus well misinformation that the American Weather Bureau used whitewash in the past. Lacquer paints are probably as old as 8000 years and I see no reason to use whitewash for a small and important weather screen. If anyone has a reliable source about paints used in the past, either inside or outside the USA, I would be very grateful.



Related posts

Changes in screen design leading to temperature trend biases

Temperature bias from the village heat island

Temperature trend biases due to urbanization and siting quality changes

Climatologists have manipulated data to REDUCE global warming

Homogenisation of monthly and annual data from surface stations

References

Cook, B.I., S.P. Shukla, M.J. Puma, L.S. Nazarenko, 2014: Irrigation as an historical climate forcing. Climate Dynamics, 10.1007/s00382-014-2204-7.

Siebert, Stefan, Jippe Hoogeveen, Petra Döll, Jean-Marc Faurès, Sebastian Feick and Karen Frenken, 2006: The Digital Global Map of Irrigation Areas – Development and Validation of Map Version 4. Conference on International Agricultural Research for Development. Tropentag 2006, University of Bonn, October 11-13, 2006.

Siebert, S., Kummu, M., Porkka, M., Döll, P., Ramankutty, N., and Scanlon, B.R., 2015: A global data set of the extent of irrigated land from 1900 to 2005. Hydrology and Earth System Sciences, 19, pp. 1521-1545, doi: 10.5194/hess-19-1521-2015.

Tuesday, 31 March 2015

Temperature trend biases due to urbanization and siting quality changes

The temperature in urban areas can be several degrees higher than their surrounding due to the Urban Heat Island (UHI). The additional heat stress is an important medical problem and studied by bio-meteorologists. Many urban geographers study the UHI and ways to reduce the heat stress. Their work suggests that the UHI is due to a reduction in evaporation from bare soil and vegetation in city centers. The solar energy that is not used for evaporation goes into warming of the air. In case of high-rise buildings there are, in addition, more surfaces and thus more storage of heat in the buildings during the day, which is released during the night. High-rise buildings also reduce radiative cooling (infrared) at night because the surface sees a smaller part of the cold sky. Recent work suggests that cities also influence convection (often visible as cumulus (towering) clouds).

To study changes in the temperature, a constant UHI bias is no problem. The problem is an increase in urbanization. For some city stations this can be clearly seen in a comparison with nearby rural stations. A clear example is the temperature at the station in Tokyo, where the temperature since 1920 rises faster than in surrounding stations.



Scientists like to make a strong case, thus before they confidently state that the global temperature is increasing, they have naturally studied the influence of urbanization in detail. An early example is Joseph Kincer of the US Weather Bureau (HT @GuyCallendar) who studied the influence of growing cities in 1933.

While urbanization can be clearly seen for some stations, the effect on the global mean temperature is small. The Fourth Assessment Report from the IPCC, states the following.
Studies that have looked at hemispheric and global scales conclude that any urban-related trend is an order of magnitude smaller than decadal and longer time-scale trends evident in the series (e.g., Jones et al., 1990; Peterson et al., 1999). This result could partly be attributed to the omission from the gridded data set of a small number of sites (<1%) with clear urban-related warming trends. ... Accordingly, this assessment adds the same level of urban warming uncertainty as in the TAR: 0.006°C per decade since 1900 for land, and 0.002°C per decade since 1900 for blended land with ocean, as ocean UHI is zero.
Next to the removal of urban stations, the influence of urbanization is reduced by statistical removal of non-climatic changes (homogenization). The most overlooked aspect may, however, be that urban stations do not often stay at the same location, but rather are relocated when the surrounding is seen to be no longer suited or the meteorological offices simply cannot pay the rent any more or the offices are relocated to airports to help with air traffic safety.

Thus urbanization does not only lead to an gradual increase in temperature, but also to downward jumps. Such a non-climatic change often looks like an (irregular) sawtooth. This can lead to artificial trends in both directions; see sketch below. In the end, what counts is how strong the UHI was in the beginning and how strong it is now.



The first post of this series was about a new study that showed that even villages have a small "urban heat island". For a village in Sweden (Haparanda) and Germany (Geisenheim) the study found that the current location of the weather station is about 0.5°C (1°F) colder than the village center. For cities you would expect a larger effect.

Around the Second World War many city stations were moved to airports, which largely takes the stations out of the urban heat island. Comparing the temperature trend of stations that are currently at airports with the non-airport stations, a number of people have found that this effect is about 0.1°C for the airport stations, which would suggest that it is not important for the entire dataset.

This 0.1°C sounds rather small to me. If we have urban heat islands of multiple degrees and people worry about small increases in the urban heat island effect, then taking a station (mostly) out of the heat island should lead to a strong cooling. Furthermore, cities are often in valleys and coasts and the later build airports thus often are at a higher and thus cooler location.

A preliminary study by citizen scientist Caerbannog suggests that airport relocations can explain a considerable part of the adjustments. These calculations need to be performed more carefully and we need to understand why the apparently small difference for airport stations translates to a considerable effect for the global mean. A more detailed scientific study on relocations to airports is unfortunately still missing.

Also the period where the bias increases in GHCNv3 corresponds to the period around the second world war where many stations were relocated to airports, see figure below. Finally, also that the temperature trend bias in the raw GHCNv3 data is larger than the bias in the Berkeley Earth dataset suggests that airport relocations could be important. Airport stations are overrepresented in GHCNv3, which contains a quite large fraction of airport stations.



With some colleagues we have started the Parallel Observations Science Team (POST) in the International Surface Temperature Initiative. There are some people interested in using parallel measurements (simultaneous measurements at cities and airports) to study the influence of these relocations. There seems to be more data than one may think. We are, however, still looking for a leading author (hint).

If the non-climatic change due to airport relocations is different (likely larger) than the change implemented in GHCNv3, that would give us an estimate of how well homogenization methods can reduce trend biases. Williams, Menne, and Thorne (2012) showed that homogenization can reduce trend errors, that they improve trend estimates, but also that part of the bias remains.



In the 19th century and earlier, thermometers were expensive scientific instruments and meteorological observations were made by educated people, apothecaries, teachers, clergymen, and so on. These people lived in the city. Many stations have subsequently been moved to better and colder locations. Whether urbanization produces a cold or a warm bias is thus an empirical and historical question. The evidence seems to show that on average the effect is small. It would be valuable when the effect of urbanization and relocations would be studies together. That may lead to an understanding of this paradox.



Related posts

Changes in screen design leading to temperature trend biases

Temperature bias from the village heat island

Climatologists have manipulated data to REDUCE global warming

Homogenisation of monthly and annual data from surface stations

Sunday, 8 March 2015

How can the pause be both ‘false’ and caused by something?

Judith Curry asked Michael Mann:
"How can the pause be both ‘false’ and caused by something?"
She really did, if you do not believe me, here is the link to her blog post.

I have trouble seeing a contradiction, but I have seen this meme more often among the mitigation sceptics. Questions like, how can you claim there is no hiatus when so many scientists are studying it?

Let's first formulate it abstractly, then give a neutral example, before we go to the climate change case where some people suddenly become too creative.

Abstract

"How can the pause be false" can be translated to: how can you claim A is still related to t?

While "caused by something" can be translated to: A is also related to X, Y, and Z.

I hope the abstract case makes clear that you can claim that A is related to X, Y and Z without claiming that A is not related to t.

Neutral

The neutral, I hope, analogues argumentation would be: How can the claim that economic growth needs free markets, property rights and rule of law be true, at a time that economists are studying the influence of the [[Lehman Brothers]] crash on economic growth?

I know, analogies do not work in the climate "debate". Someone will always claim that they do not fit. Which is always right. That is why they are called analogies.

Climate

There is no statistically significant change in the trend. People who think they see that in a the temperature signal are often just shown a small part of the data and they overestimate the significance of short-term trends. The uncertainty in a 10-year trend is not 10 times as large as the uncertainty of a 100-year trend. A 10-year trend is 100 times more uncertain.

That there is no change in the temperature trend is visually clearly seen by these two elegant graphs made by Tamino.




What causes these deviations from the trend line or the deviations from the average model projections is naturally an interesting question. Something that climatologists used to simply call: natural variability, small stuff, impossible to understand in detail.

It is a great feat that climatologists now dare to say something about these minor deviations. Remember that we had more than half a degree of warming over many decades before climatologists said with any kind of confidence that global warming is real.

Even if these dare devils turn out to be wrong, it tells a lot about the quality of our modern climate monitoring capabilities, climate models and analysis tools, that scientists are willing to stick their neck out and say: I think I know what might have caused these minimal deviations of a tenth, maybe two tenth of a degree Celsius. Pretty amazing.


Friday, 27 February 2015

Stop all harassment of all scientists now

This week Greenpeace revealed that aerospace engineer Willie Soon got funding of over one million dollars from the fossil fuel industry and related organizations. However, Soon did not declare these conflicts of interest, while many scientific journals he wrote for do require this. His home institution is now investigating these irregularities.

Possibly inspired by this event, Member of the U.S. House of Representatives for Arizona Raúl M. Grijalva (Dem) has requested information on funding of seven mitigation sceptical scientists that have testified before the US congress. Next to funding also the drafts of the testimonies and any correspondence about them are requested. The seven letters went to the employers of: David Legates, John Christy, Judith Curry, Richard Lindzen, Robert Balling, Roger Pielke and Steven Hayward.

This is harassment of scientists for their politically inconvenient positions. That is wrong and should not happen. This is a violation of the freedom of research.

Judith Curry and Roger Pielke Jr. are on twitter and I was happy to see that basically everyone agreed that targeting scientists for political aims is wrong. There was a lot of support for them from all sides of this weird US climate "debate".


[UPDATE. The American Meteorological Society also sees these letters as wrong: "Publicly singling out specific researchers based on perspectives they have expressed and implying a failure to appropriately disclose funding sources — and thereby questioning their scientific integrity — sends a chilling message to all academic researchers... We encourage the Committee to rely on the full corpus of peer-reviewed literature on climate science as the most reliable source for knowledge and understanding that can be applied to the policy options before you."]

After these signs of solidarity, maybe this is the right moment to agree that all harassment of all scientists is wrong and change the rules. I would personally prefer that the Freedom of Science gets constitutional rank everywhere, like it already has in Germany having learned from the meddling in science during the Third Reich. At least we should change the law and stop the harassment, especially by the governments and politicians.

Next to the affair around Willie Soon, the open record requests by Democrat Rep. Grijalva may also have been inspired by the plans of Oklahoma Republican Sen. Jim Inhofe and California Republican Rep. Dana Rohrabacher. They announced this week their plans to investigate the politically inconvenient temperature record of NASA-GISS. This not too long after a congressional audit which kept the scientists of the National Climate Data Centre (NOAA-NCDN) from their important work.

The new investigation of GISS is all the more ironic as the GISS dataset is nowadays basically the NCDC dataset, but with a reduced trend due to an additional attempt to reduce the effect of urbanization. Probably these two mitigation sceptical politician do not even know that they will investigate an institution that makes the trend smaller. Just like most mitigation sceptics do not seem to know that the net effect of all adjustments for non-climatic changes is a reduction in global warming.

It is not as if this was the first harassment of inconvenient climate scientists. As the Union of Concerned Scientists writes:
Notably, the requests from Rep. Grijalva are considerably less invasive than a request made in 2005 by Rep. Joe Barton for materials from Penn State climate scientist Michael Mann. Rep. Barton’s request sought not only funding information but also data, computer code, research methods, information related to his participation in the Intergovernmental Panel on Climate Change (including report reviewers), and detailed justifications of several of his scientific calculations. The Barton requests were roundly condemned by scientists, and were part of a long history of harassment of Dr. Mann and his colleagues.

Then we did not yet mention the report in which Republican Senator James Inhofe called for the persecution of 17 named inconvenient climate scientists and more not named scientists. We did not yet mention the political attack of the Republican Attorney General Ken Cuccinelli on Michael Mann, which the Virginia Supreme Court halted after costing the university nearly $600,000 for legal fees.

The harassment is not limited to the USA. There was an action of the mitigation sceptics to ask Phil Jones of the UK Climate Research Unit (CRU) for the data and contracts with the weather services for five random countries. The same Phil Jones of the politically inconvenient CRUT global temperature curve whose emails were stolen and widely distributed by the mitigation sceptics. Emails which did not contain any evidence of wrongdoings, but spreading them is an efficient way to punish Jones for his inconvenient work by hurting his professional network.

In New Zealand, the Member of Parliament Mr. Hide filed 80 parliamentary questions to the the maintainers of the temperature record of New Zealand. As a result the minister requested an audit by the Australian Weather Service, which costed the researchers several months of work. The mitigation sceptics in New Zealand have on started a foundation for juridical attacks. When the judge ordered these mitigation sceptics to pay the costs of the trail, NZ$89,000, the foundation filed for bankruptcy, leaving the tax payers with the costs.

Open records laws

Open records does not help to check a scientific consensus. Scientists judge the evidence collectively, as historian of science Naomi Orekes states. Chris Mooney writes, in a beautiful piece on motivated reasoning, explains that this means that individual scientists are not important:
We should trust the scientific community as a whole but not necessarily any individual scientist. Individual scientists will have many biases, to be sure. But the community of scientists contains many voices, many different agendas, many different skill sets. The more diverse, the better.
This may come as a surprise to people who get their science from blogs or mass media. Mitigation sceptical blogs like to single out a small number of public scientists. Possibly not to make it visible how many scientists stand behind our understanding of climate change, possibly to dissuade other scientists from speaking in public.

Journalists like to focus on people and tell stories about how single persons revolutionised entire scientific fields. Even in the most medially hyped examples of clearly brilliant scientists such as Einstein and Feynman this is not true. If other scientists had not checked the consequences of their claims, these claims would have been a cry in deep vacuum. Journalists also tend to exaggerate the importance of single (new) scientific articles with spectacular and thus make the huge number of less sexy articles invisible.

These journalists would like to be allowed to do almost anything for a juicy story. In the Columbia Journalism Review, a journalist complained that exemptions for science “made it difficult for journalists to look into (Penn State’s) football sex abuse scandal.” I fail to see why journalists should have extra rights to investigate sex scandals, when they happen at public institutions. If they want more rights, then everyone should be affected, also private universities, companies and journalists. Personally I am not sure if I want to live in such a post-privacy world.

This kind of invasion of privacy has real consequences. I notice that colleagues in countries with Freedom of Information Act (FoIA) harassment write short and formal mails, whereas they are just as talkative at conferences or on the telephone. That is only natural, when you write for the front page of the New York Times you put in more effort to make sure that every detail is right and clear. If you have to put in that amount of effort for every mail to a colleague, you naturally write less. This hinders scholarly communication.

Mitigation sceptics that are convinced that top scientists control science and determine what is acceptable for publication should welcome strong confidentiality even more. That allows the honest scientists to build a coalition and get rid of these supposedly dishonest scientists. More realistically, scientists need to be able to warn their colleagues about errors in the work or character of other people.

Finally, scientists are also humans and write about private things. That is important to keep networks strong. The more so because for many science is not just a profession, but a vocation. Thus boundaries between private and work can be vague.

Thus I would argue that scientific findings should be checked by scientists. That includes everyone who invested the time to make himself an expert, not just the professionals. However, that is not the role of journalists and certainly not of politicians.

Openness

There are naturally cases where the public may want to know more about what is happening at academic institutions. The funding of science is a good example. It has been shown that the funding source influences the results of medical research. This should thus be disclosed.

Industry funding of science is welcome, but it should happen openly. Representatives of industry have complained that that would make it impossible for them to collaborate with universities, because that would give competing firms strategic information and would allow them to copy the ideas. I would argue that when the research is that straightforward, it is not something for a university.

At some universities in Switzerland and at the University of Cologne there have recently been protests against companies funding large amounts of research and about contractual conditions that limit scientists in their work. This can also limit the freedom of science and we need rules for this. It should not lead to a situation where industry research is sold as independent academic research.

It should never be possible to firms to stop the publication of results. A contract with Willie Soon stated that he was not allowed to disclose his funding. I feel such conditions should not be allowed. Some people complained about contractual obligations or scientists to inform the firms of their work. I would feel that that is still okay, it is natural that the firms are interested in a transfer the knowledge. Also in case of larger joint projects, scientists are expected to show up at general meetings of the project.

Sometimes replication of scientific work is hard, for example in case of large dietary studies or clinical trails. This makes it hard for scientists to check such research without access to the original data. Also in climatology it would be very beneficial if the governments around the world would allow a free transfer of observational data. Climate data is often withheld for commercial and military reasons. While climate data is valuable, the number of people willing to pay for them is small and the fees minimal. The military value of climate data is disappearing due to the accuracy of modern global weather predictions.

In all the above cases and maybe more, we should not work with open record laws, but make the information open for everyone for every case. In this way these laws cannot be abused for attacks on scientists doing politically inconvenient work. Criminal investigations should naturally be possible, scientists are humans, but should never, ever be ordered by politicians, such as in the case of Senator Inhofe. We should protect the separation of powers, such political orders should be illegal.



Related reading

Climate of Incivility - Climate McCarthyism is Wrong Whether Democratic or Republican
Michael Shellenberger of the [[Break Through Institute]] agree that the political intimidation of science from any side should stop.

An insider’s story of the global attack on climate science.
Jim Salinger, who produced a temperature dataset for New Zealand, talks about how he and this employer were harassed by politicians and mitigation sceptics.

What Kinds of Scrutiny of Scientists are Legitimate?
Michael Halpern of the Union of Concerned Scientists argues that the information requests send to the 7 mitigation sceptics go too far: the funding requests are appropriate, but communication between researchers should be protected.

He is also the author of a detailed report: Freedom to Bully: How Laws Intended to Free Information Are Used to Harass Researchers.

No Scientist Should Face Harassment. Period.
Gretchen Goldman of the Union of Concerned Scientists want to limit open records requests: "Science is an iterative process and researchers should be free to discuss, challenge, and develop ideas with a certain level of privacy."

Stoat: Raúl M. Grijalva is an idiot. He’s a politician and be relying on his own ability to evaluate what’s said. Or in the case of climate science, just read the IPCC report, its what its here for.

My Depressing Day With A Famous Climate Skeptic
Astrophysics professor Adam Frank: "What I had seen was a scientist whose work, in my opinion, was simply not very good. ... But Soon's little string of papers were being heralded in the highest courts of public opinion as a significant blow to everyone else's understanding of Earth's climate."

Why scientists often hate records requests, The shadow side of sunlight laws
Anna Clark of the Columbia Journalism Review writes about open records requests from the side of journalists and advocates teaching people how to make the requests not too intrusive.

Why all we believe our own favorite scientific ‘experts’ — and why they believe themselves
Chris Mooney on motivated reasoning. Great, clear exposition.

Democrats on climate 'witch hunt', conservatives say
politico reports on the 7 letters and lists several mitigation sceptics that complain now, but did not see any problems with attacks against climate scientists in the past.

Thursday, 12 February 2015

Just the facts, homogenization adjustments reduce global warming

Climatologists make adjustments to climate data to remove non-climatic changes (homogenization). This fact is used to accuse them of fiddling with temperature data to create or exaggerate global warming. This is often done by showing for a small piece of the data and suggesting it is typical. Often mentioned is the USA, where the raw data only show half the warming of the adjusted data. However, the USA is big, but still only 2% of the Earth's surface.

In recent weeks we had a similar case in The Telegraph about Paraguay. Last year we had similar misleading stories about two stations in Australia and the stations in New Zealand.

Global temperature collections contain thousands of stations. CRUTEM contains 4,842 quality stations and Berkeley Earth collected 39,000 unique stations. No wonder some are strongly adjusted up, just as some happen to be strongly adjusted down. In fact it would be easy to present a station where the raw data shows a cooling trend of several degrees being adjusted to a warming trend. However, then the reader might start to think if the raw data is really better.

The information on small regions or a few stations is normally not put into perspective: the average trend over all stations is only adjusted upwards slightly.

It is normally not explained why these adjustments are made nor how these adjustments are made.

Zeke Hausfather, an independent researcher that is working with Berkeley Earth, made a beautiful series of plots to show the size of the adjustments.

The first plot is for the land surface temperature from climate stations. The data is from the Global Historical Climate Dataset (GHCNv3) of NOAA (USA). Their method to remove non-climatic effects (homogenization) is well validated and recommended by the homogenization community.

They adjust the trend upwards. In the raw data the trend is 0.6°C per century since 1880 while after removal of non-climatic effects it becomes 0.8°C per century. See the graph below. But it is far from changing a cooling trend into strong warming. (A small part of the GHCNv3 raw data was already homogenized before they received it, but this will not change the story much.)



Not many people know, however, that the sea surface temperature trend is adjusted downward. These downward adjustments happen to be about the same size, but go into the other direction. See below the sea surface temperature of the Hadley Centre (HadSST3) of the UK MetOffice.



Being land creatures people do not always realise how big the ocean is, but 71% of the Earth is ocean. Thus if you combine these two temperature signals taking the area of the land and the ocean into account you get the result below. The net effect of the adjustments is a reduction of global warming.



It is pure coincidence that this happens, the reasons for the adjustments are fully different.

The land surface temperature trend has to be adjusted up because old temperatures were often too high due to insufficient protection against warming by the sun, possibly because the siting of the stations improved and there are likely more reasons.

The old sea surface temperature are adjusted downward because old measurements were made by taking a bucket of water out of the ocean and the water cooled by evaporation during the measurement. Furthermore, modern measurements are made at the water inlet of the engine and the hull of the ship warms the water a little before it is measured.

But while it is a pure coincidence and while other datasets may show somewhat different numbers (the BEST adjustments are smaller), the downward adjustment does clearly show that climatologists do not have an agenda to exaggerate global warming. That would still be true if the adjustments had happened to go upward.



Related reading

Phil Plait at Bad Astronomy comment on the Telegraph piece: No, Adjusting Temperature Measurements Is Not a Scandal

Kevin Cowtan made two videos on the claim of the Telegraph on Paraguay and the Arctic. The second video shows how to check such claims yourself.

John Timmer at Ars Technica is also fed up with being served the same story about some upward adjusted stations every year: Temperature data is not “the biggest scientific scandal ever” Do we have to go through this every year?

The astronomer behind And Then There's Physics writes why the removal of non-climatic effects makes sense. In the comments he talks about adjustments made to astronomical data. Probably every numerical observational discipline of science performs data processing to improve the accuracy of their analysis.

Steven Mosher, a climate "sceptic" who has studied the temperature record in detail and is no longer sceptical about that reminds of all the adjustments demanded by the "sceptics".

Nick Stokes, an Australian scientist, has a beautiful post that explains the small adjustments to the land surface temperature in more detail.

My two most recent posts were about some reasons for temperature trend biases: Temperature bias from the village heat island and Changes in screen design leading to temperature trend biases

You may also be interested in the posts on how homogenization methods work (Statistical homogenisation for dummies) and how they are validated (New article: Benchmarking homogenisation algorithms for monthly data)

Tuesday, 10 February 2015

Climatologists have manipulated data to REDUCE global warming

Climatologists are continually accused of fiddling with the data to make global warming stronger for political purposes by political activists.

A typical scam is to show a few stations that have been adjusted upwards and act as if that is typical. For example, recently The Telegraph article, "The fiddling with temperature data is the biggest science scandal ever", wrote about someone comparing
temperature graphs for three weather stations in Paraguay against the temperatures that had originally been recorded. In each instance, the actual trend of 60 years of data had been dramatically reversed, so that a cooling trend was changed to one that showed a marked warming.
Three, I repeat: 3 stations. For comparison, global temperature collections contain thousands of stations. CRUTEM contains 4,842 quality stations and Berkeley Earth collected 39,000 unique stations. No wonder some are strongly adjusted up, just as some happen to be strongly adjusted down. In fact it would be easy to present a station where the raw data shows a decreasing trend of several degrees being adjusted upwards, but then the reader might start to think if the raw data is really better.

What these people do not tell their readers is that the average trend over all station is only adjusted upwards slightly. That would put things too much in perspective. What these people do not tell their readers is why these adjustments are made. That might make some think that it may make sense. What these people normally do not tell their readers is how these adjustments are made. That would not sound sufficiently arbitrary and conspirational.

Last year we had similar scams about two stations in Australia and the stations in New Zealand.

In an internet poll, 88% of the readers of the abysmal Telegraph piece agree with the question: "Has global warming been exaggerated by scientists?"

I hope that after reading this post, these 88% will agree that they have been conned by The Telegraph. That scientists have actually made global warming smaller.

Zeke Hausfather, an independent researcher that is working with Berkeley Earth, made a beautiful series of plots to show the size of the adjustments.

The first plot is for the land surface temperature from climate stations. The data is from the Global Historical Climate Dataset (GHCNv3) of NOAA (USA). Their method to remove non-climatic effects (homogenization) is well validated and recommended by the homogenization community.

They adjust the trend upwards. In the raw data the trend is 0.6°C per century since 1880 while after removal of non-climatic effects it becomes 0.8°C per century. See below. But it is far from changing a cooling trend into strong warming.

(In case you believe many national weather services are also in the conspiracy: a small part of the GHCNv3 raw data was already homogenized before they received it.)



Not many people know, however, that the sea surface temperature trend is adjusted downward. That does not fit the narrative of WUWT & Co. It sounds like even many scientists did not know that. These downward adjustments happen to be about the same size, but go into the other direction. See below the sea surface temperature of the Hadley Centre (HadSST3) of the UK MetOffice.



Being land creatures people do not always realise how big the ocean is. Thus if you combine these two temperature signals taking the area of the land and the ocean into account you get the result below. The net effect of the adjustments is a reduction of global warming.



It is pure coincidence that this happens, the reasons for the adjustments are fully different.

The land surface temperature trend has to be adjusted up because old temperatures were often too high due to insufficient protection against warming by the sun and possibly because the siting of the stations improved. There are likely more reasons.

The sea surface temperature are adjusted downward because old measurements were made by taking a bucket of water out of the ocean and the water cooled by evaporation during the temperature measurement. Furthermore, modern measurements are made at the water inlet of the engine and the hull of the ship warms the water a little before it is measured.

But while it is a pure coincidence and while other datasets may show somewhat different numbers (the BEST adjustments are smaller), the downward adjustment does clearly show that climatologists do not have an agenda to exaggerate global warming. Like all reasonable people already knew. That would still be true if the adjustments had happened to go upward.

[UPDATE:

Small networks

The smaller the networks, the larger the size of the non-climatic changes typically is.

A recent paper about the US mountain network (SNOWTEL) explained that their mountain stations showed more warming than the lower lying USHCN stations. This could be a snow-albedo feedback (that the warming reduces the white snow and reveals the dark surface leading to more warming. However they found it was a non-climatic change in the temperature due to in the installation of new equipment. The new instruments recorded about 1.5°C higher minimum temperatures; an extraordinary large change (the maximum temperature was hardly affected). Accurate data is not just important for trends, but also for physics (snow-albedo feedback).

That is another case of climatologists reducing warming and a feedback.

But what did a well-know blog of the mitigation sceptics, WUWT, write? They headlined: "Another bias in temperature measurements discovered" and opened: "From the “temperature bias only goes one way department”".

The second comment is by "cg": "Lying in Weather Reporting is common place and shamelessly just like the Global Financiers want it. Pure Evil."
Brute: "You sound insane."
KaiserDerden: "no more insane than you do claiming CO2 controls the weather/climate… actually less so in fact ...
Brute: "I have never said a single word regarding how “CO2 controls the weather/climate”. It is curious how much paranoia one finds around here... just about as much as one finds among the warmist cults...."
Sun Spot: "@Brute, you sound sanctimonious"
Ofay Cat: "CG ... you have it right ... those others are uninformed or misinformed. Which means Liberal."
cg: "Thanks"
]

Let's end on a depression note. Rob Honeycutt says:
Take note. Proving the conspiracy wrong is sure to be taken as proof you’re part of the conspiracy.

It would be interesting to track, but I somehow doubt the number of “skeptic” posts with accusations of fraud is going to change. And I think this is merely because the source of the “skepticism” isn’t rooted in true scientific skepticism. It’s formed on an ideological basis. So, asking them to accept the data as correct is the same, from their standpoint, as asking them to change their ideology.

End of rant. Sorry for the tone. One sometimes gets the impression that WUWT & Co. select the most stupid memes possible to produce the largest antagonistic effect possible. It would be too easy to talk about the real caveats, the ones also mentioned by the enemy in the IPCC reports. For example, that assessing the impacts of climate change is enormously difficult because it involves ecosystems and humans. For example, that estimating trends in extreme weather is very challenging and very much current research; also partially due to non-climatic changes in the daily data.

[UPDATE. This version got a bit snarkier than usual, which maybe warranted in talking to hardcore mitigation sceptics. To link to in discussions with people who might be open for debate, I have written a second matter-of-fact version: Just the facts, homogenization adjustments reduce global warming. In case of doubt, when you do not know people well, that is probably also the best version.]



Related reading

Phil Plait at Bad Astronomy comment on the Telegraph piece: No, Adjusting Temperature Measurements Is Not a Scandal

John Timmer at Ars Technica is also fed up with being served the same story about some upward adjusted stations every year: Temperature data is not “the biggest scientific scandal ever” Do we have to go through this every year?

The astronomer behind And Then There's Physics writes why the removal of non-climatic effects makes sense. In the comments he talks about adjustments made to astronomical data. Probably every numerical observational discipline of science performs data processing to improve the accuracy of their analysis.

Steven Mosher, a climate "sceptic" who has studied the temperature record in detail and is no longer sceptical about that reminds of all the adjustments demanded by the "sceptics".

Nick Stokes, an Australian scientist, has a beautiful post that explains the small adjustments to the land surface temperature in more detail.

My two most recent posts were about some reasons for temperature trend biases: Temperature bias from the village heat island and Changes in screen design leading to temperature trend biases

You may also be interested in the posts on how homogenization methods work (Statistical homogenisation for dummies) and how they are validated (New article: Benchmarking homogenisation algorithms for monthly data)