Gavin Schmidt, supermodeller: the emergent patterns of climate change

In this new TED talk, Gavin Schmidt, NASA climate modeller and juggler extraordinaire, talks about the climate system, how we use models, how they’re put together, and how the great swirls of earth’s atmosphere emerge from a million lines of Fortran code. It’s a great exposition, and the graphics he calls up in support are magnificent.

Big guns brought to bear

homer.jpgThe now infamous McLean, de Freitas and Carter paper in the Journal of Geophysical Research (see Mother Nature’s Sons) has attracted a damning response from some of the biggest names in climate science, including a strong Kiwi contribution*. A comment has been submitted to JGR by Grant Foster, James Annan, Phil Jones, Michael Mann, Brett Mullan, Jim Renwick, Jim Salinger, Gavin Schmidt, and Kevin Trenberth. McLean et al’s “analysis is incorrect”, “seriously overestimates” the link between ENSO and global temperatures, and their paper provides no support for any claim about recent global temperature trends. Here’s the abstract:

McLean et al. [2009] (henceforth MFC09) claim that the El Nino/Southern Oscillation (ENSO), as represented by the Southern Oscillation Index (SOI), accounts for as much as 72% of the global tropospheric temperature anomaly (GTTA) and an even higher 81% of this anomaly in the tropics. They conclude that the SOI is a “dominant and consistent influence on mean global temperatures,” “and perhaps recent trends in global temperatures”. However, their analysis is incorrect in a number of ways, and greatly overstates the influence of ENSO on the climate system. This comment first briefly reviews what is understood about the influence of ENSO on global temperatures, then goes on to show that the analysis of MFC09 severely overestimates the correlation between temperature anomalies and the SOI by inflating the power in the 2–6 year time window while filtering out variability on longer and shorter time scales. It is only because of this faulty analysis that they are able to claim such extremely high correlations. The suggestion in their conclusions that ENSO may be a major contributor to recent trends in global temperature is not supported by their analysis or any physical theory presented in that paper, especially as the analysis method itself eliminates the influence of trends on the purported correlations.

Looks to me like there’s no academic wiggle room for McLean, de Freitas and Carter. They got it very wrong. The big question now is how they managed to sneak the paper through peer-review. Meanwhile, claims that McLean et al shows “that most of the late 20th century global warming and cooling can be attributed to natural climate processes” will remain up at crank web sites, and Carter and de Freitas will consider their real work — to provide more propaganda for the denial machine — well done.

[* Brett Mullan and Jim Renwick are at NIWA, Jim Salinger’s now in the same department at Auckland University as CdF (which must make for interesting conversation over morning coffee), and Kevin Trenberth is a New Zealander.]

Picturing the Science

Climate Change: Picturing the Science

“It is simply the best available collection of essays by climate scientists on the nature of human-induced climate change, the ways scientists have come to understand and measure the risks that it poses, and the options that we face.”
Thus Jeffrey Sachs in his foreword to Climate Change: Picturing the Science edited by Gavin Schmidt and Joshua Wolfe. He has a somewhat proprietary interest in the publication in that much of it is written by scientists associated with his Columbia University’s Earth Institute, but his declaration is not overblown.

Gavin Schmidt is well known to readers of the RealClimate website, of which he was a co-founder. He is a climate scientist at NASA’s Goddard Institute for Space Studies.  Joshua Wolfe is a documentary photographer much of whose work focuses on climate change.  His is one of three splendid photo essays which punctuate the book, along with many other carefully selected illustrative photographs on almost every page.

Medical terms head the book’s three parts – symptoms, diagnosis and possible cures.  Seven climate scientists contribute chapters with one or two experts in technology and policy joining them in part three.

The symptoms section has five headings: the unequivocal warming of the globe; the changes occurring in the Arctic; changes to the chemistry, biology and level of the sea; the likelihood of extreme events; the threat to biodiversity. In all these areas troubles are already apparent or can be seen developing.

The diagnosis section has three chapters.  The first describes the drivers of climate and the part played by anthropogenic forcings.  The second explains the study of climate “one of the most complex and lively branches in all of Earth science.”  Dozens of different fields are involved. The chapter lists some of them: meteorology, oceanography, biology, chemistry, quantum physics, orbital mechanics, and ecology. It has a useful characterisation of the four overlapping groups into which climate scientists can be broadly split: those studying the physical processes in the current climate system, others looking for indications of how and why climates were different in the past, yet others documenting the impacts of change today, and some bringing all these elements together to try and say something about the future.  The third chapter discusses prognoses for that future, making a helpful distinction between forecasts, predictions and projections before examining prospects for rising temperatures, rainfall changes, rising sea levels, ocean changes, greenhouse gas feedbacks, decreasing biodiversity, human health risks, and agricultural impacts. Surprises are inevitable, and they are not likely to be benign.

These two sections of the book are straightforward explanations of where the science stands today.  They acknowledge plenty of uncertainties. Schmidt states that the book has eschewed polemics “in favour of a ‘warts and all’ exposition of what we know, what we don’t know, and what is already being seen.”  The tone is restrained, the content factual.  The complexities of the science are not compromised, but the findings are laid out in terms that any general reader can comprehend.  Although the path to understanding what is going on has its complications, and there have been major intellectual feats (and sometimes physical ones as well) along the way as the clues have been put together, the basic picture which has emerged is not hard to grasp.

Turning to possible cures in the book’s third section the various, now familiar technologies are surveyed and the political aspects of emission reduction explored.  The difficulties of adequate action and internationally agreed policy are acknowledged, but a degree of somewhat dogged hope also finds expression.

Slightly aside from the main thrust of the book, it’s worth drawing attention to a couple of the brief contributions which interleave the major chapters.  Elizabeth Kolbert (whose Field Notes from a Catastrophe was my introduction to the seriousness of climate change) has an illuminating reflection on why it has been hard for journalism to communicate the reality of global warming.  Naomi Oreskes writes thoughtfully about the scientific consensus on climate change and why it is under no challenge from contrarian claims.

We need to see climate scientists making the kind of communication to the public this book represents.  Straight from the horse’s mouth.  I don’t imagine all scientists would relish the task, but certainly those chosen for this publication write clearly and accessibly for the lay person. The reader gets not only a survey of where things stand in the areas each of the writers is engaged with but also an awareness of the scope and range of the scientific activity associated with climate change. I doubt most people are aware of the magnitude of the scientific attention the subject is now receiving.

A full picture is what the book provides, mostly through words but also through the striking images which accompany the text.  It will be a very helpful aid to readers who want to see that full picture, either because they don’t have hold of it yet or because they want to fill in gaps in their understanding.

It is a large, handsomely produced volume which will adorn any surface on which it lies while its reader works through it. Not at one sitting, I would suggest, but filling in the picture slowly chapter by chapter.