In case you missed it (ICYMI), a couple of new papers have been published recently, demonstrating that there has not been any "pause" or "hiatus" in surface temperature in recent years. Yes, the rate of increase wasn't as high as it has been in some other periods. However these papers demonstrate that there was nothing different from what can be expected from a warming trend with interannual variability imposed on it.
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.
|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.
|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)