MODEL-OBSERVATION COMPARISON 1958-2012 IN THE TROPICAL TROPOSPHERE
Tim Vogelsang and I published a paper in Environmetrics called
In it we compare the temperature trends in climate models over the 1958-2012 interval in the tropical troposphere to those observed in weather balloon data. The models tend not only to over-predict observed warming, but also to represent it differently. Models exhibit a relatively smooth upward trend, whereas observations show almost all the warming took place in a single jump in the late 1970s and the trend either side is practically and statistically zero. Since the tropical troposphere is where models predict the maximum response to GHG forcing should be observed, the absence of a significant trend there over a 55-year interval is a serious inconsistency. Data and code are here. A discussion at Climate Audit is here.
COMMENTARY & TECHNICAL REPORTS
POLICY IMPLICATIONS OF THE PAUSE IN GLOBAL WARMING
I have published a report for the Fraser Institute looking at the economic policy implications of the lack of global warming. Had the situation been reversed, namely had there been much more warming than models projected over the past 20 years, there would likely be loud calls for a policy response, namely a ramping up of current plans and targets. The same reasoning applies under the opposite circumstances, namely that there was much less warming than models projected. Fundamentally the problem is that the policy models are trained to match climate models, not climate data, and this needs to change.
My report argues for building a more robust connection between empirical findings on climate processes and the economic models that generate climate policy plans.
A STATISTICALLY-ROBUST DEFINITION OF THE LENGTH OF THE GLOBAL WARMING PAUSE
I have published a paper proposing a definition of the length of the pause that is robust to autocorrelation and cherry-picking endpoints.
CLIMATE MODELS INABILITY TO GET THE SPATIAL TREND PATTERN RIGHT:
Lise Tole and I published a paper in Climate Dynamics testing the ability of climate models to reproduce the spatial pattern of temperature trends over land. This builds on previous work of mine looking at the correlation between indicators of industrial development over land and the spatial pattern of warming trends, a relationship that is not predicted by models and is supposed to have been filtered out of the surface climate record. The paper is
MODEL-DATA TREND COMPARISONS FOR THE TROPICAL TROPOSPHERE:
My first foray into this topic looks at how to compare model-generated trends to observations. There have been some rather simplistic methods used before now, based on t-stats with "effective degrees of freedom" adjustments &whatnot. The following paper explains more accurate testing methods using panel regression and multivariate trend estimations that have higher power and greater robustness to complex autocorrelation patterns. The application is to the tropical troposphere, an important regions for testing models' ability to quantify the atmospheric response to greenhouse gases. A few recent studies differed on whether models significantly overstate the warming or not. We find that up to 1999 there was only weak evidence for this, but on updated data the models appear to significantly overpredict warming.
CORRECTION to MMH10: In 2010 Steve, Chad and I published a paper that applied panel and multivariate (VF) methods to test the significance of trends and of model-obs differences in the tropical troposphere. There were a couple of typos, and also Chad discovered an error in the GISS data as archived at the PCMDI (not a huge one, just an error splicing pre- and post-2000 runs together). We re-did our analyses and used the updated versions of the observational data for the purpose. The correction has been published:
The GISS correction and data revisions strengthen all our original findings, reducing the observational trends and raising (slightly) the model trends. (a) The combined MSU trends have a p-value just over 0.05; still significant but "marginal". (b) The HadAT 1979-2009 trend in the LT drops from significance to marginal. (c) The average 1979-2009 MT trend across all observational series drops to insignificance. (d) The RICH 1979-2009 MT trend drops to insignificance. (e) The RSS 1979-2009 MT series is now significantly different from models in the panel regression test. For the 1979-2009 interval, all observational series individually and jointly are significantly below models at both the LT and MT layers. (f) Over the 1979-1999 interval the model-obs differences are still marginally significant but in the MT layer it is now at about the 6% level, so it is nearly significant.
THE GLOBAL WARMING HIATUS, aka DISCREPANCY
I have a column today (June 17 2014) in the Financial Post on the widening discrepancy between models and observations. The talk of the "pause" in global warming is somewhat misplaced, since a pause is not out of place amidst a long term upward trend. What is out of place is an extended pause just where models predict a sharp rise. That's the issue that merits attention, both for the scientific issues it gives rise to, and also the potential policy implications. NOTE: the line shades were mislabeled in the article--black should be gray and vice-versa. The above graph has the correct shading. R code to draw that graph is here.