No, we do not have 12 years to stop catastrophic climate change #12years

I have to apologize to Peter Hadfield (better known as Potholer54) as I am not sure I have found the source of the talking point that we only have 12 years. Science journalist Hadfield always encourages real skeptics to check claims by searching for the source in the scientific literature. The best solution to the riddle I found is really disappointing, but independent of the source, the claim is terrible.

How much warming is seen as acceptable is a political compromise between how hard it is to change the energy system (against powerful vested interests) and how much damages people see as acceptable. All world leaders have agreed in the Paris climate agreement on the following compromise.

Holding the increase in the global average temperature to well below 2°C [3.6°F] above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C [2.7 °F] above pre-industrial levels, recognising that this would significantly reduce the risks and impacts of climate change.

Previously the political compromise used to be to keep the warming below 2°C and most scientific work thus focused on the impacts of 2°C warming and on possible ways to make the transition that fast. After Paris politicians asked scientists to study how much the damages from climate change would be reduced and how much harder it would be to limit warming to 1.5°C.

The Intergovernmental Panel on Climate Change (IPCC) thus brought all the research on this topic together and in October published a report on the difference between 1.5°C and 2°C warming. In the media reporting a frequent talking point somehow was that we only have 12 years to stop climate change.

How much CO2 can we still emit?

Before looking into it I had guessed the claim would be based on the carbon budget. How much CO2 we can still emit until we reach the amount that will likely warm the Earth by 1.5°C. Note that CO2 accumulates in the climate system and the warming is determined by the total historical amount we emit. I sometimes worry people think that when global warming becomes too devastating we can stop emitting CO2 and the problem is solved. When the French stopped dumping salt in the Rhine and Meuse the water quality quickly became better. CO2 is not like that. When we stop emitting CO2 warming will even continue for some time, it will not go back to the temperature we used to have and many consequences (such as sea level rise) will keep getting worse, just slower.



The Earth has already warmed by about 1°C since the end of the 19th century.* Based on past emissions alone we would not reach the 1.5°C warming level yet, according to the IPCC report. A part of the carbon budget is still left. This is a bit more than 10 times how much we currently emit per year and could thus have been the source of the talking point. The Summary for Policy Makers of the IPCC states:

Limiting global warming requires limiting the total cumulative global anthropogenic emissions of CO2 since the pre-industrial period, that is, staying within a total carbon budget (high confidence). By the end of 2017, anthropogenic CO2 emissions since the pre-industrial period are estimated to have reduced the total carbon budget for 1.5°C by approximately 2200 ± 320 GtCO2 (medium confidence). The associated remaining budget is being depleted by current emissions of 42 ± 3 GtCO2 per year (high confidence). The choice of the measure of global temperature affects the estimated remaining carbon budget. Using global mean surface air temperature, as in AR5, gives an estimate of the remaining carbon budget of 580 GtCO2 for a 50% probability of limiting warming to 1.5°C, and 420 GtCO2 for a 66% probability (medium confidence).

This would have been a better reason for the talking point than the possible reason below, but even then we do not have 12 years, we should do more NOW. We cannot wait 12 years and then suddenly stop all emissions. We are already doing a lot, half of all new electrical generation capacity in the world is already renewable power, but we need to do more and do this now. The only time better than now is decades ago.

---

The best time to start [reducing emissions] was 25 years ago. The second best time is today.

---

On the other hand, the Earth does not explode in 12 years, any action reduces damages and adaptation costs. If we do not manage to limit the warming to 1.5°C, it would be better to limit it to 1.6°C than to 1.7°C, and so on. There is no brick wall we crash into, there is no cliff we fall into, there is no "deadline", CNN. Any limitation of the warming makes life on Earth better. Being lied into one Iraq war is catastrophic, but still better than 2 or 3 wars.

Any analogy is imperfect, but a better analogy would be that climate change is like crossing a busy street without looking, it is a irresponsible risk and the farther you go the higher the risk. Another analogy is walking into a mine field as Michael Mann often says. We do not know when the mines will explode, better walk into the field as little as possible and not 12 meters.

Reducing CO2 emission means changing our energy system and agriculture. This is a big task, and not something we will not be finished within 12 years. When we do more now, we would also have more time than 12 years to finish the task.

It is much better to say that to achieve the climate goals we have set ourselves in the Paris climate agreement we have to be at zero emissions in a generation. Or that we have to half emissions in 2030.

I would vote for that, but considering the resistance to change of the establishment, Gavin Schmidt is probably realistic when writing on RealClimate:

Can we avoid going through 1.5ºC?

IPCC has to use a few circumlocutions to avoid giving a direct answer to this question (for reasonable and understandable reasons). I’m not quite so constrained…

There are many issues related to the feasibility question of which physical climate-related issues are only one. The basic issue is that the effort to reduce emissions sufficiently to never get past 1.5ºC would require a global effort to decarbonize starting immediately that would dwarf current efforts or pledges. This seems unlikely (IMO).
...
So my answer is… no.

I get that there is reluctance to say this publically – it sounds as if one is complicit in the impacts that will occur above 1.5ºC, but it seems to me that tractable challenges are more motivating than impossible (or extremely unfeasible) ones – I would be happy to be proven wrong on this though.

The craziness begins

However, the press articles and TV segments on the IPCC report do not talk about the carbon budget. In most cases they do not explain at all where the 12 years comes from. The Guardian headline is: "We have 12 years to limit climate change catastrophe, warns UN." Given that English is the global language, the difficulty of the English have understanding international relations is rather surprising. The IPCC is not the UN. More importantly for this post, the headline is not explained anywhere in the article.

The most surprising place to see the claim is Fox News**: "Terrifying climate change warning: 12 years until we’re doomed." That is some contrast to their evening television opinion shows operating as the PR arm of the Republican party. This article was on their homepage, in the science section, under the category "Doomsday" and republishing an article written by the New York Post. Again I cannot find a justification for the headline in the article.

The Sunrise Movement will visit members of Congress to lobby for a Green New Deal on Monday, December the 10th and would like climate scientists, who happen to meet at the AGU Fall meeting in Washington DC, to join them. They also did not go to the source, but trusted newspapers when they write in their call for action: "the latest UN report says we have 12 years to rapidly transform our economy to protect human civilization as we know it."

As an aside, had I been in Washington, I would have been happy to join them, I feel we need to do more to reduce climate change damages, but the Green New Deal is politics, not science. So I would not show up as a scientist (in one of those stereotypical white lab coats).



We may be getting a bit closer to the solution listening to CNN. Interrupting their programming on the missing Malaysia Airlines aircraft CNN titles "Planet has only until 2030 to stem catastrophic climate change, experts warn" and says: "In Paris leaders pledge to keep the rise well below 2 degrees [Celsius]. This report now suggests we aim for 1.5°C. A benchmark we are predicted to reach in 2030."

(No, the politicians suggested we'd aim for 1.5°C.) Why does CNN think that experts warned about this? The reporting of LifeGate may give a hint:

If not curbed, this trend will lead the Earth to exceed the threshold of +1.5 degrees between 2030 and 2052 (according to the different scenarios the SR15 took into consideration). This means that in just 12 years we could reach the temperature rise that the Paris Agreement hypothesised for 2100.

LifeGate is a news organization calling itself "the leading point of reference for sustainable development since 2000". They at least describe this situation is sufficient detail to have a look what the source says.

What does the IPCC say about 1.5°C, 2030 and 2052? The summary for policy makers states in their description of the current situation:

Human activities are estimated to have caused approximately 1.0°C of global warming above pre-industrial levels, with a likely range of 0.8°C to 1.2°C. Global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate. (high confidence)

Chapter one of the report has the details and confirms that the period 2030 to 2052 is based on an estimate of how much the world has warmed up to now and how fast it is warming. That fits, we have warmed about 1°C and the warming is about 0.2°C per decade. So one degree more warming would be in 5 decades and half a degree warming more would be 25 years, which is the middle of the 2030 to 2052 year interval.


Figure SMP1, panel a, from the Summary for Policy Makers of the IPPC Special Report on Global Warming of 1.5°C.

This is the warming baseline WUWT & Co., Big Coal and Big Oil and the pro-torture politicians Trump, Jair Bolsonaro and Mohammad Bone Saw Salman are fighting for, which is for comparison with climate policies that benefit humanity in the remainder of the report.

The period of 2030 to 2052 is mentioned in the beginning of the report and was also mentioned early in the IPCC press conference. So it makes sense that is was noted in the press, but that they used the lower uncertainty range (12 years) and not the mean (26 years) is weird, as well as calling reaching the 1.5°C level an immediate catastrophe or deadline, while it had a different function.

Maybe I am too much of a scientist, but mentioning the lower boundary of an uncertainty range makes no sense without defining the range. The IPCC used the term "likely", which is defined as a probability between 66 and 100%. If you wanted to more sure the period contains the year we will cross the 1.5°C level, for example "virtually certain" (99-100%), the range would have been much wider and the lower bound much earlier. Scientifically speaking the "12 years" without that context is meaningless.

So what most likely happened is that we have scientists describing the progression of climate change. They give the uncertainty range and the press decides to only mention the lower boundary of this range. Then they somehow turn it into a deadline, put this in many headlines and never tell their readers where the number comes from. This made #12years a somewhat viral political meme. Chinese whispers of the worst kind. Journalists please listen to Peter Hadfield: check the source.




* If we define the pre-industrial temperature as the temperature of the second half of the 19th century, as the newest IPCC report did. The actual industrial revolution and our CO2 emissions started a century earlier. Politicians will have to clarify how they define their thresholds. It may be a good idea to convert the 1.5°C and 2°C limits into warming since a more recent period, as this is better defined due to much better observations.

** Clicking on the Fox News link may give you "Access Denied". Copy and paste works.

Related reading

Professor Myles Allen lead author of the IPCC Special Report on Global Warming of 1.5°C: Why protesters [everyone, red.] should be wary of ‘12 years to climate breakdown’ rhetoric.

The Carbon Brief: In-depth Q&A: The IPCC’s special report on climate change at 1.5C

Andrew King, Ben Henley & Ed Hawkins in The Conversation: What is a pre-industrial climate and why does it matter?

Special Report: Global Warming of 1.5 ºC

There’s one key takeaway from last week’s IPCC report. Cut carbon pollution as much as possible, as fast as possible.

Largest ever group of global investors call for more action to meet Paris targets. 'The group of 414 institutional investors with $31 trillion under management say governments must take serious steps to cut emissions. ... Among specific policies, they request governments “phase out thermal coal power”, “put a meaningful price on carbon” and “phase out fossil fuel subsidies.”'

In the ongoing climate negotitions in Poland, Saudi Arabia, the US, Russia & Kuwait objected to the conference "welcoming" the IPCC Special Report on 1.5°C warming, the BBC reports. The flood of messages on this BBC article suggests that climate scientists who volunteered to write the report are not amused.

The IPCC underestimates global warming

A month ago the New York Times insulted its subscribers with a climate change column by Bret Stephens, their new hire from the Wall Street Journal. The bizarre text was mostly a sequence of claims that did not follow from the arguments presented.

The column also contained one fact. Which was wrong and later corrected. Stephens claimed:

Anyone who has read the 2014 report of the Intergovernmental Panel on Climate Change knows that, while the modest (0.85 degrees Celsius, or about 1.5 degrees Fahrenheit) warming of the Northern Hemisphere since 1880 is indisputable, as is the human influence on that warming, much else that passes as accepted fact is really a matter of probabilities.

As a dutiful watcher of Potholer54, which any real skeptic should be, you know that it is a good idea to check the source and Stephens helpfully provided a link to the Summary for Policymakers of the 5th assessment synthesis report of the Intergovernmental Panel on Climate Change (IPCC). This summary mentions the number "0.85" in the sentence:

The globally averaged combined land and ocean surface temperature data as calculated by a linear trend show a warming of 0.85 [0.65 to 1.06] °C over the period 1880 to 2012, when multiple independently produced datasets exist (Figure SPM.1a). {1.1.1, Figure 1.1}

Figure SPM.1a. Annually and globally averaged combined land and ocean surface temperature anomalies relative to the average over the period 1986 to 2005. Colours indicate different data sets.

Thus Stephens confused the global temperature with the temperature of the Northern Hemisphere. Not a biggy, but indicative of the quality of Stephens' writing.

A related weird claim is that the "warming of the earth since 1880 is indisputable, as is the human influence on that warming, much else that passes as accepted fact is really a matter of probabilities."

As quoted above the warming since 1880 is not exactly known, but probably between 0.65 and 1.06 °C. That it was warming is so certain that a journalist may call it "indisputable". There is thus no conflict between probabilities and certainty. In fact they go hand in hand. When scientists talk about uncertainties, they are quantifying how certain we are.

However, I did not want to attack the soft target Bret Stephens. The hard target IPCC is much more interesting. They put some thought in their writing.

More precisely I have problems when they write in the summary for policy makers: "temperature data as calculated by a linear trend show a warming of 0.85". That means that they fitted a linear function to the data — using [[least squares regression]] — and used this trend and the length of the period to estimate the total warming over this period.

This is a problem because calculating the total amount of warming using a linear trend underestimates global warming.* I show this below for two global temperature datasets by comparing the linear warming estimate with a nonlinear (LOESS) warming estimate. The linear estimate is smaller: For NASA's GISTEMP it is 0.05 °C smaller and for Berkeley Earth it is 0.1 °C smaller.



Such linear estimates are well suited for comparing different datasets because it is well defined how to compute a linear trend and the bias will be similar in the different datasets. That is why linear estimates are used a lot in the scientific literature and scientists reading this know that a linear estimate can be biased when the curve itself is not linear.

But this was a warming estimate for the summary for policy makers. Policy makers and the public in general should get an unbiased estimate of the climatic changes we have seen and are before us.

Tending to underplay the problem is quite typical. There is even an article on climate Scientists Erring on the Side of Least Drama and also The Copenhagen Diagnosis gives several examples such as the very low predictions for the decline in sea ice or the increase in sea level.

When it comes the warming found in station data, we did study the main possible warming bias (urbanization) in depth, but hardly did any work on cooling biases that may lead us to underestimate the amount of warming.

In a recent study to define what "pre-industrial" means when it comes to the 2 °C warming limit, the authors suggest a comparison period with relatively few volcanoes, which is thus relatively warm. This underestimates the warming since "pre-industrial". The authors wanted to be "conservative". I think we should be unbiased.

I understand that scientists want to be careful before crying wolf, whether we have a problem or not. However, when it comes to the size of the wolf, we should give our best estimate and not continually err on the side of a Chihuahua.

Related reading

Climate Scientists Erring on the Side of Least Drama

Why raw temperatures show too little global warming

The NY Times promised to fact check their new climate denier columnist — they lied

* The linear estimate is typically smaller, sometimes a lot, whether the actual underlying function is convex or concave. I had expected this estimate to be always smaller, but noticed while writing this post that for polynomial functions, f(t) = t^p, it can also be a few percent higher for p between 1 and 2. Below you can see 4 example curves, where the time runs between zero and one and thus also f(t) goes from zero to one. The total "warming" in all cases is exactly one. The linear estimates are generally less than one, except for the f(t) = t^1.5 example.

The bottom graph shows these linear estimates as a function of exponent p, where you can see that for an exponent between 1 (linear) and 2 (quadratic) the estimates can be a little higher than one, while they are generally lower. Probably Carl Friedrich Gauss or at least Paul Lévy already wrote an article about this, but it was a small surprise to me.




** Top photo of a Chihuahua is licensed under the Creative Commons Attribution 3.0 Unported license.
Bottom Chihuahua photo by Inanishi is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0) license.


*** The R code to generate the plots with the linear and nonlinear warming from two global temperature datasets is on GitHub. The R code to study the influence of the polynomial exponent on the linear estimate is also on GitHub.

Did you notice the recent anti-IPCC article?

You may have missed the latest attack on the IPCC, because the mitigation sceptics did not celebrated it. Normally they like to claim that the job of scientists is to write IPCC friendly articles. Maybe because that is the world they know, that is how their think tanks function, that is what they would be willing to do for their political movement. The claim is naturally wrong and it illustrates that they are either willing to lie for their movement or do not have a clue how science works.

It is the job of a scientist to understand the world better and thus to change the way we currently see the world. It is the fun of being a scientist to challenge old ideas.

The case in point last week was naturally the new NOAA assessment of the global mean temperature trend (Karl et al., 2015). The new assessment only produced minimal changes, but NOAA made that interesting by claiming the IPCC was wrong about the "hiatus". The abstract boldly states:

Here we present an updated global surface temperature analysis that reveals that global trends are higher than reported by the IPCC ...

The introduction starts:

The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded that the global surface temperature “has shown a much smaller increasing linear trend over the past 15 years [1998-2012] than over the past 30 to 60 years.” ... We address all three of these [changes in the observation methods], none of which were included in our previous analysis used in the IPCC report.

Later Karl et al. write, that they are better than the IPCC:

These analyses have surmised that incomplete Arctic coverage also affects the trends from our analysis as reported by IPCC. We address this issue as well.

To stress the controversy they explicitly use the IPCC periods:

Our analysis also suggests that short- and long-term warming rates are far more similar than previously estimated in IPCC. The difference between the trends in two periods used in IPCC (1998-2012 and 1951-2012) is an illustrative metric: the trends for these two periods in the new analysis differ by 0.043°C/dec compared to 0.078°C/dec in the old analysis reported by IPCC.

The final punchline goes:

Indeed, based on our new analysis, the IPCC’s statement of two years ago – that the global surface temperature “has shown a much smaller increasing linear trend over the past 15 years than over the past 30 to 60 years” – is no longer valid.

And they make the IPCC periods visually stand out in their main figure.


Figure from Karl et al. (2015) showing the trend difference for the old and new assessment over a number of periods, the IPCC periods and their own. The circles are the old dataset, the squares the new one and the triangles depict the new data with interpolation of the Arctic datagap.

This is a clear example of scientists attacking the orthodoxy because it is done so blatantly. Normally scientific articles do this more subtly, which has the disadvantage that the public does not notice it happening. Normally scientists would mention the old work casually, often the expect their colleagues to know which specific studies are (partially) criticized. Maybe NOAA found it easier to use this language this time because they did not write about a specific colleague, but about a group and a strong group.

Figure SPM.1. (a) Observed global mean combined land and ocean surface temperature anomalies, from 1850 to 2012 from three data sets. Top panel: annual mean values. Bottom panel: decadal mean values including the estimate of uncertainty for one dataset (black). Anomalies are relative to the mean of 1961−1990. (b) Map of the observed surface temperature change from 1901 to 2012 derived from temperature trends determined by linear regression from one dataset (orange line in panel a).

The attack is also somewhat unfair. The IPCC clearly stated that it not a good idea to focus on such short periods:

In addition to robust multi-decadal warming, global mean surface temperature exhibits substantial decadal and interannual variability (see Figure SPM.1). Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends. As one example, the rate of warming over the past 15 years (1998–2012; 0.05 [–0.05 to 0.15] °C per decade), which begins with a strong El Niño, is smaller than the rate calculated since 1951 (1951–2012; 0.12 [0.08 to 0.14] °C per decade)

What the IPCC missed in this case is that the problem goes beyond natural variability, that another problem is whether the data quality is high enough to talk about such subtle variations.

The mitigation sceptics may have missed that NOAA attacked the IPCC consensus because the article also attacked the one thing they somehow hold dear: the "hiatus".

I must admit that I originally thought that the emphasis the mitigation sceptics put on the "hiatus" was because they mainly value annoying "greenies" and what better way to do so than to give your most ridiculous argument. Ignore the temperature rise over the last century, start your "hiatus" in a hot super El Nino year and stupidly claim that global warming has stopped.

But they really cling to it, they already wrote well over a dozen NOAA protest posts at WUWT, an important blog of the mitigation sceptical movement. The Daily Kos even wrote: "climate denier heads exploded all over the internet."

This "hiatus" fad provided Karl et al. (2015) the public interest — or interdisciplinary relevance as these journals call that — and made it a Science paper. Without the weird climate "debate", it would have been an article for a good climate journal. Without challenging the orthodoxy, it would have been an article for a simple data journal.

Let me close this post with a video of Richard Alley explaining even more enthusiastic than usually
what drives (climate) scientists? Hint: it ain't parroting the IPCC. (Even if their reports are very helpful.)

Suppose Einstein had stood up and said, I have worked very hard and I have discovered that Newton is right and I have nothing to add. Would anyone ever know who Einstein was?

Tweet

Further reading

My draft was already written before I noticed that at Real Climate Stefan Rahmstorf had written: Debate in the noise.

My previous post on the NOAA assessment asked the question whether the data is good enough to see something like a "hiatus" and stressed the need to climate data sharing and building up a global reference network. It was frivolously called: No! Ah! Part II. The return of the uncertainty monster.

Zeke Hausfather: Whither the pause? NOAA reports no recent slowdown in warming. This post provides a comprehensive, well-readable (I think) overview of the NOAA article.

How climatology treats sceptics. My experience fits to what you would expect.

References

IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp, doi: 10.1017/CBO9781107415324.

Thomas R. Karl, Anthony Arguez, Boyin Huang, Jay H. Lawrimore, James R. McMahon, Matthew J. Menne, Thomas C. Peterson, Russell S. Vose, Huai-Min Zhang, 2015: Possible artifacts of data biases in the recent global surface warming hiatus. Science. doi: 10.1126/science.aaa5632.

Boyin Huang, Viva F. Banzon, Eric Freeman, Jay Lawrimore, Wei Liu, Thomas C. Peterson, Thomas M. Smith, Peter W. Thorne, Scott D. Woodruff, and Huai-Min Zhang, 2015: Extended Reconstructed Sea Surface Temperature Version 4 (ERSST.v4). Part I: Upgrades and Intercomparisons. Journal Climate, 28, pp. 911–930, doi: 10.1175/JCLI-D-14-00006.1.

Rennie, Jared, Jay Lawrimore, Byron Gleason, Peter Thorne, Colin Morice, Matthew Menne, Claude Williams, Waldenio Gambi de Almeida, John Christy, Meaghan Flannery, Masahito Ishihara, Kenji Kamiguchi, Abert Klein Tank, Albert Mhanda, David Lister, Vyacheslav Razuvaev, Madeleine Renom, Matilde Rusticucci, Jeremy Tandy, Steven Worley, Victor Venema, William Angel, Manola Brunet, Bob Dattore, Howard Diamond, Matthew Lazzara, Frank Le Blancq, Juerg Luterbacher, Hermann Maechel, Jayashree Revadekar, Russell Vose, Xungang Yin, 2014: The International Surface Temperature Initiative global land surface databank: monthly temperature data version 1 release description and methods. Geoscience Data Journal, 1, pp. 75–102, doi: 10.1002/gdj3.8.

Testimony Judith Curry on Arctic temperature seems to be a misquotation

Looks like the IPCC is not even wrong.

There has been a heated debate between Judith Curry (Climate Etc.) and Tamino (Open Mind) about the temperature in the Arctic. This debate was initiated by Curry's testimony before congress two weeks ago.

In her testimony Judith Curry quotes:

“Arctic temperature anomalies in the 1930s were apparently as large as those in the 1990s and 2000s. There is still considerable discussion of the ultimate causes of the warm temperature anomalies that occurred in the Arctic in the 1920s and 1930s.” (AR5 Chapter 10)

Tamino at Open Mind investigated this claim and found that recent temperatures were clearly higher as in the beginning of the 20th century. In his post (One of) the Problem(s) with Judith Curry Tamino concludes that the last IPCC report and Curry's testimony are wrong about the Arctic temperature increase:

"I think the IPCC goofed on this one — big-time — and if so, then Curry’s essential argument about Arctic sea ice is out the window. I’ve studied the data. Not only does it fail to support the claim about 1930s Arctic temperatures, it actually contradicts that claim. By a wide margin. It ain’t even close."

That sounded convincing, but I am not so sure about the IPCC any more.

Tamino furthermore wonders where Curry got her information from. I guess he found it funny that Judith Curry would quote the IPCC as a reliable source without checking the information. Replying to another question of mine, Judith Curry replied on twitter that she indeed got her information from the last (draft) IPCC report:

@VariabilityBlog I will deal with this nonsense on friday on my blog. I QUOTED the IPCC AR5
— Judith Curry (@curryja) January 21, 2014

Later she also wrote a reply on her blog, Climate Ect., starting with the above quote from the IPCC report.

Then the story takes a surprising turn, when Steve Bloom hidden in a large number of comments at AndThenTheresPhysics notes that the quote is missing important context. The full paragraph in the IPCC namely reads (my emphasis and the quote in Curry's testimony in red):

A question as recently as six years ago was whether the recent Arctic warming and sea ice loss was unique in the instrumental record and whether the observed trend would continue (Serreze et al., 2007). Arctic temperature anomalies in the 1930s were apparently as large as those in the 1990s and 2000s. There is still considerable discussion of the ultimate causes of the warm temperature anomalies that occurred in the Arctic in the 1920s and 1930s (Ahlmann, 1948; Veryard, 1963; Hegerl et al., 2007a; Hegerl et al., 2007b). The early 20th century warm period, while reflected in the hemispheric average air temperature record (Brohan et al., 2006), did not appear consistently in the mid-latitudes nor on the Pacific side of the Arctic (Johannessen et al., 2004; Wood and Overland, 2010). Polyakov et al. (2003) argued that the Arctic air temperature records reflected a natural cycle of about 50–80 years. However, many authors (Bengtsson et al., 2004; Grant et al., 2009; Wood and Overland, 2010; Brönnimann et al., 2012) instead link the 1930s temperatures to internal variability in the North Atlantic atmospheric and ocean circulation as a single episode that was sustained by ocean and sea ice processes in the Arctic and north Atlantic. The Arctic wide temperature increases in the last decade contrast with the episodic regional increases in the early 20th century, suggesting that it is unlikely that recent increases are due to the same primary climate process as the early 20th century. IPCC(2014, draft, page 10-43 to 10-44).

Steve Bloom dryly comments: "So it was a question in 2007." In other words, the IPCC was right, but Judith Curry selectively quoted from the report. That first sentence is very important, also the age of the references could have revealed that this paragraph was not discussing the current state-of-the-art. The data of the last six years makes a large difference between "with some goodwill in the same range of temperatures" to "clearly higher Arctic temperatures".

This is illustrated by one of the figures from Tamino's post, presenting the data:

This is the annual average temperature in the Arctic from 60 to 90 degrees North as computed by the Berkeley Earth Surface Temperature group. The smooth red line is computed using LOESS smoothing.

And the misquotation is not for lack of space in the testimony. In her blog post, Curry quotes many sections of the IPCC report at length and also the entire paragraph like it is displayed here, just somehow without the first sentence printed here in bold, the one that provides the important context.

---

Related reading

The congressional Testimony by Curry: STATEMENT TO THE COMMITTEE ON ENVIRONMENT AND PUBLIC WORKS OF THE UNITED STATES SENATE Hearing on “Review of the President’s Climate Action Plan" 16 January 2014, Judith A. Curry.

(One of) the Problem(s) with Judith Curry by Tamino at Open Mind.

The reply by Curry about Tamino's post on her blog, Climate ect.

The answer to that by Tamino suggests that Curry's reply is not that convincing.

Also Robert Way contributed to the discussion at Skeptical Science: "A Historical Perspective on Arctic Warming: Part One". Robert Way made the round in the blog-o-sphere with the paper Cowtan and Way (2013), where they studied the recent strong warming in the Arctic and suggested that that may explain a part of the recent slowdown in the warming of surface temperature.

A previous post of mine of Curry's testimony, focussing on her suggestive, but non-committal language: "Interesting what the interesting Judith Curry finds interesting".

Reviews of the IPCC review

The first IPCC report (Working Group One), "Climate Change 2013, the physical science basis", has just been released.

One way to judge the reliability of a source, is to see what it states about a topic you are knowledgeable about. I work on homogenization of station climate data and was thus interested in the question how well the IPCC report presents the scientific state-of-the-art on the uncertainties in trend estimates due to historical changes in climate monitoring practices.

Furthermore, I have asked some colleague climate science bloggers to review the IPCC report on their areas of expertise. You find these reviews of the IPCC review report at the end of the post as they come in. I have found most of these colleagues via the beautiful list with climate science bloggers of Doug McNeall.

Large-Scale Records and their Uncertainties

The IPCC report is nicely structured. The part that deals with the quality of the land surface temperature observations is in Chapter 2 Observations: Atmosphere and Surface, Section 2.4 Changes in Temperature, Subsection 2.4.1 Land-Surface Air Temperature, Subsubsection 2.4.1.1 Large-Scale Records and their Uncertainties.

The relevant paragraph reads (my paragraph breaks for easier reading):

Particular controversy since AR4 [the last fourth IPCC report, vv] has surrounded the LSAT [land surface air temperature, vv] record over the United States, focussed upon siting quality of stations in the US Historical Climatology Network (USHCN) and implications for long-term trends. Most sites exhibit poor current siting as assessed against official WMO [World Meteorological Organisation, vv] siting guidance, and may be expected to suffer potentially large siting-induced absolute biases (Fall et al., 2011).

However, overall biases for the network since the 1980s are likely dominated by instrument type (since replacement of Stevenson screens with maximum minimum temperature systems (MMTS) in the 1980s at the majority of sites), rather than siting biases (Menne et al., 2010; Williams et al., 2012).

A new automated homogeneity assessment approach (also used in GHCNv3, Menne and Williams, 2009) was developed that has been shown to perform as well or better than other contemporary approaches (Venema et al., 2012). This homogenization procedure likely removes much of the bias related to the network-wide changes in the 1980s (Menne et al., 2010; Fall et al., 2011; Williams et al., 2012).

Williams et al. (2012) produced an ensemble of dataset realisations using perturbed settings of this procedure and concluded through assessment against plausible test cases that there existed a propensity to under-estimate adjustments. This propensity is critically dependent upon the (unknown) nature of the inhomogeneities in the raw data records.

Their homogenization increases both minimum temperature and maximum temperature centennial-timescale United States average LSAT trends. Since 1979 these adjusted data agree with a range of reanalysis products whereas the raw records do not (Fall et al., 2010; Vose et al., 2012a).

I would argue that this is a fair summary of the state of the scientific literature. That naturally does not mean that all statements are true, just that it fits to the current scientific understanding of the quality of the temperature observations over land. People claiming that there are large trend biases in the temperature observations, will need to explain what is wrong with Venema et al. (an article of mine from 2012) and especially Williams et al. (2012). Williams et al. (2012) provides strong evidence that if there is a bias in the raw observational data, homogenization can improve the trend estimate, but it will normally not remove the bias fully.

Personally, I would be very surprised if someone would find substantial trend biases in the homogenized US American temperature observations. Due to the high station density, this dataset can be investigated and homogenized very well.