Change points of global temperature: Cahill, Rahmstorf and Parnell
If you're a fan of realclimate.org (the benchmark of world best practice in climate blogs), then you might remember the change point analysis written up there last December, by Stefan Rahmstorf. The article was called "Recent global warming trends: significant or paused or what?" This new work looks to be on the same topic written as a peer-reviewed paper in IOP Science: "Change points of global temperature". It's open access so you can read it at your leisure.
As the authors point out (my emphasis):
While close to 50 papers have already been published on the 'hiatus' or 'pause' (Lewandowsky et al, in press), the important question of whether there has been a detectable change in the warming trend (rather than just variability in short-term trends due to stochastic temperature variations) has received little attention.
The bottom line is that there was no discontinuity in surface temperature indicating a statistically significant change point in recent years. The figure below is from the paper, and shows where change points did occur: 1907-1920, 1934-1948 and 1963-1979. But not in recent years.
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| Figure 1. Overlaid on the raw data are the mean curves predicted by the three CP model. The grey time intervals display the total range of the 95% confidence limits for each CP. The average rates of rise per decade for the three latter periods are 0.13 ± 0.04 °C, −0.03 ± 0.04 °C and 0.17 ± 0.03 °C for HadCRUT, 0.14 ± 0.03 °C, −0.01 ± 0.04 °C and 0.15 ± 0.02 °C for NOAA, 0.15 ± 0.05 °C, −0.03 ± 0.04 °C and 0.18 ± 0.03 °C for Cowtan and Way and 0.14 ± 0.04 °C, −0.01 ± 0.04 °C and 0.16 ± 0.02 °C for GISTEMP. Source: Cahill15 |
Trend pattern since 1970: Foster and Abraham
The other paper is by Grant Foster and John Abraham, and was published in US CLIVAR Variations. They took a different (and complementary) approach to the problem. In this paper the authors discuss the above study and explained what they, Foster and Abraham, did:
First, the analysis of Cahill et al. (2015) identifies the search period: with their final change-point in 1970, the relevant question to answer is whether the trend has changed since 1970. Hence we will study the data from 1970 onward in an attempt to show that it reveals some trend pattern other than just a linear rise at constant rate.
Here is their conclusion - there was no change in trend:
A barrage of statistical tests was applied to global surface temperature time series to search for evidence of any significant departure from a linear increase at constant rate since 1970. In every case, the analysis not only failed to establish a trend change with statistical significance, it failed by a wide margin.
Stopping the seepage
Next time some denier tries to claim that global warming stopped 16 or 18 or 19 or 23 years ago, you can now point them to these two papers :) Or you could tell them that last year was the hottest on record, and this year is shaping up to come close - maybe even beat it.
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| Data source: GISS NASA |
There's not been any "hiatus" in surface temperature. There have probably been some interesting things happening around the world. That's only to be expected as we enter unchartered territory by rapidly heating up the planet.
References and further reading
Niamh Cahill, Stefan Rahmstorf and Andrew C Parnell. "Change points of global temperature". 2015 Environ. Res. Lett. 10 084002. doi:10.1088/1748-9326/10/8/084002 (open access)
Grant Foster and John Abraham. "Lack of evidence for a slowdown in global temperature." US CLIVAR Variations • Summer 2015 • Vol. 13, No. 3 (open access)
Recent global warming trends: significant or paused or what? - by Stefan Rahmstorf at realclimate.org, December 2014
Statistics says the long-term global warming trend continues - by John Abraham in The Guardian - and at SkepticalScience.com
Where most of us live (with apologies to southern-hemisphere readers) - by Tamino
The alleged hiatus in global warming didn’t happen, new research shows - a more comprehensive article about both papers, by Greg Laden
Stephan Lewandowsky, Naomi Oreskes, James S. Risbey, Ben R. Newell and Michael Smithson. "Seepage: Climate change denial and its effect on the scientific community." Global Environmental Change, 2015 doi:10.1016/j.gloenvcha.2015.02.013 (open access)
I am no fan at all of Gavin Schmidt over at realclimate. He's done a lot of damage. It really does appear as if he's become an apologist for industry. He's taken the position that methane isn't much of a problem when there are a number of better qualified scientist in direct opposition to him. His projections / commentary lack far behind others, including who he was supposed to replace, Hansen. Schmidt has lost a huge number of participants since he took the helm.
ReplyDeleteBollocks!
Delete"Better qualified scientist" like David Archer, maybe?
Deletehttp://www.realclimate.org/index.php/archives/2013/11/arctic-and-american-methane-in-context/
Doesn't look like he's in direct opposition to Schmidt...
Well, maybe those scientists in the Permafrost Carbon Network then?
Nope, they are not in opposition to Schmidt either:
http://www.usgs.gov/newsroom/article.asp?ID=4185#.VcOhvf0w-po
Looks like Schmidt is just being a scientist. A real one.
Yep.
Delete"He's taken the position that methane isn't much of a problem when there are a number of better qualified scientist in direct opposition to him."
DeleteThe top permafrost scientists (and yes this is a permafrost issue) have addressed this issue (See Schuur et al., 2015) and basically concluded that the idea of a methane bomb from the Arctic is unrealistic. There's a lot of alarmism on this issue coming from people who do not appear to have much support within their own scientific communities.
Anon takes concern trolling to a whole new level: Gavin Schmidt an apologist for industry?! PZ Myers will be an apologist for religion next...
DeleteAbsurd charges from nowhere.
Delete"I am no fan at all of...."
DeleteI have spent days puzzling over this, but I still can't figure out why anybody would give a rat's arse what you think.
I was thinking those same thoughts myself, so I went to a psychiatrist and he discovered the brain surgeons had missed a couple of nails from my nail-gun accident.
ReplyDeleteIt's a disappointment that the IPCC and many individual researchers wobbled on this and scrambled for ad hoc explanations rather than recognizing from the outset the lack of statistical significance of the short-term trend of the post-1998 surface temperature record.
ReplyDeleteYes, some of the second-order effects hypothesized as explanations may well be valid and interesting in their own rights, but the premature invocation of a hiatus unnecessarily gave the 'skeptics' oxygen, even if the scientific consequences were negligible.
Magma.
DeleteNo, it was stated from the outset the result was sensitive to start and end points. The IPCC reported it the context of how fast was the global average temperature rising, they were being honest.
Researchers then looking for an explanation for the IPCC result is just doing science.
Personally, I think most climate scientists don't care about how their results are interpreted or used by the lunatic fringe.
I suppose they felt they had to address what had become a topical issue. Note, however, unlike denialists the authors used scare quotes around "hiatus" in the box in Chapter 9.
DeleteThen of course there is the mindset of modeling everything to the n-th degree. Physicists can hardly be blamed for that mindset but sometimes random variation really IS the relevant factor.
The truth is probably somewhere in the middle: There are likely factors which can be used to explain some parts of the remaining variation but some random error will always remain beyond the level of measurement and modelling.
@ Harry Twinotter: I partly agree on the broadest level but the various researchers and editors should have been much more explicit.
DeleteAs to interpretations or use by the lunatic fringe, unfortunately that fringe is influencing debate and public policy in, at a bare minimum, the U.S., the UK, Canada and Australia. It is incumbent on climate scientists to understand this and to write and speak VERY clearly with respect to their research results.
If I study the spread of a virus that causes a mild illness in a rare species of toad, my research is likely of interest to me and a few dozen people on Earth and any misrepresentations unimportant. In contrast, if it's the spread of Ebola or virulent new influenza strains in human populations I can rightly expect far more interest and scrutiny, and deliberate or inadvertent misrepresentations of the results may become far more consequential.
+100 Magma. This non-story has been frustrating me for years, both in terms of the deliberate ignorance and/or lying of the Denialati, and in terms of the timidity of the profession in robustly rebutting it from the outset a number of years ago.
ReplyDeleteWhat I would like to see is this recent work filtering right to the top in US politics as quickly as possible, with prominent presidential emphasis that this has always been a red herring to purposefully obfuscate from the dangerous rate of warming that has not in fact ceased.
If only the lower troposphere would cooperate!
ReplyDeleteCare to elaborate?
DeleteIsn't the lower troposphere where we are accustomed to seeing stuff cooked up by a creationist which is later debunked by somebody - anybody - who doesn't receive money from the fossil fuel industry?
DeleteAnon - go read the SKS article on the subject, then come back and talk intelligently. Or just disappear and reinforce our strongly held prior that anon drive-bys are about as intelligent as the average rock in my garden.
DeleteYour choice.
If only science denying trolls would cooperate.
DeletePerhaps Anon is referring to the RSS record which has not yet reflected the el Niño related increases the surface record show. From what I understand there tends to be several months lag between the SST and the troposphere temps.
ReplyDeletePerhaps one of the participating climate scientists could comment on this.
Didn't Tamino destroy this myth a while back?
ReplyDelete"ICYMI - there's no stopping the rise in surface temperature! "
ReplyDeleteWell.....DUH! A million people arguing about facts on the net for two years, instead of demanding from climate liars that they explain how a pause is even conceivable under the laws of physics.
But.... no matter. The important fact is that we have wasted another two years arguing with liars instead of building a new energy system. Well done, science lovers! ;(
ICYMI in the Reflubitcan Presidential Election Debate there was no mention of the heating up planet, the wildfires, nor the trillions of trees killed as a result by drought and stress related parasites & disease. No money for combatting that, there's no money for struggling Americans, no money for child poverty... But UNLIMITED money$ for WAR!
ReplyDeleteFrom people who avoided serving in the Armed Services when given the opportunity.
The real winners of the debate? Anyone who didn't watch it...
It was all lies, lies and more lies. The hot whopper was probably Jeb Bush saying Obama created ISIL by pulling out of Iraq when his brother Dubya had made it mandatory to pull all troops out!
And Smokey-DB Stealey-D Boehm-db is back spreading bullshyyyyyt the Clinton Foundation does their charitable donations directly, mostly not through other organizations. You can count on nothing but LIES from Da Bull Shyt spreader too!
Suggestion, the next GOP debate should be moved to Washington State, it would look more like reality!
ReplyDelete