IPCC AR5 WG1

Just in case you aren’t that involved in the climate change/global warming debate, the acronyms in my post title mean Intergovernmental Panel on Climate Change (IPCC) Assessment Report 5 (AR5) Working Group 1 (WG1). The IPCC is in the process of releasing all it’s reports. A couple of days ago, they released the Summary for Policy Makers (SPM) and today they’ve released the final draft of the Working Group 1 (WG1) report. It’s a remarkably long document and I haven’t had a chance to read much (or any for that matter). I’m already impressed by those on Twitter who’ve already managed to find some mistakes (or at least what they think are mistakes). That takes real dedication and commitment.

There was one thing I was going to briefly comment on, and that is the figure below. I have seen it before but that was from a leaked draft of the report, and so I didn’t want to comment until the report was officially released. The figure shows comparisons between observations and model results and includes both regional comparisons and global comparisons. I think it’s a fascinating figure for a number of reasons.

1. It’s clear that the models are remarkably complicated, and include the atmosphere, land, sea surface, oceans, and sea ice. They are also able to model individual regions as well as producing global comparisons.
2. Models without anthropogenic forcings (blue lines and blue regions) are clearly unable to reproduce the observed changes. Models including both anthropogenic and natural forcings (red lines and pink regions) do a remarkable job of reproducing the observations (black). This is one of the reasons for the claim that we are now 95% certain that most of the warming since 1950 is anthropogenic. The WG1 document says, when discussing this figure,
   

   Human influence has been detected in nearly all of the major assessed components of the climate system (Figure TS.12). Taken together, the combined evidence increases the overall level of confidence in the attribution of observed climate change, and reduces the uncertainties associated with assessment based on a single climate variable. From this combined evidence it is virtually certain that human influence has warmed the global climate system.

3. The models appear to do quite a good job of matching the rise in ocean heat content. Since about 90% of the energy excess goes into the oceans, this would suggest that the models are accurately reproducing the global energy budget.
4. The main talking point for those “skeptical” of climate change is that the models have not matched/predicted the slowdown in surface warming since the late 1990s. Firstly, the models are still technically consistent with the observations. Furthermore, the models clearly do much more than simply attempt to predict the change in surface temperatures and so focusing on this one thing would, in my opinion, be ignoring all the others aspects of the models that are all relevant to our understanding of global warming/climate change.

So, I think the figure is a really good illustration of how well we understand both the fundamentals and details of global warming. Of course, there may be subtleties that I don’t realise or appreciate. If so, feel free to correct me through the comments.

Comparison between observations and model results (decadal averages), at regional scales (top panels) and global scales (bottom 4 panels). Brown panels are land surface temperature time series, blue panels are ocean heat content time series, and white panels are sea-ice time series. Each panel shows observations (black or black and shades of grey), and the 5–95% range of the simulated response to natural forcings (blue shading) and natural and anthropogenic forcings (pink shading), together with the corresponding ensemble means (dark blue and dark red respectively). The observed surface temperature is from HadCRUT4.

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