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.
Small networksThe 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."
Let's end on a depressive note. Rob Honeycutt says:
Take note. Proving the conspiracy wrong is sure to be taken as proof you’re part of the conspiracy.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.
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.
[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 readingIf you need a peer reviewed reference, the influence of the adjustments on the global mean temperature is also shown in Karl et al. (2015).
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)