Climate warming has slowed but, given the loading of heat-trapping greenhouse gases in the atmosphere, scientists have every reason to expect it will pick back up again very soon – perhaps in earnest. But what if it doesn’t? Or what if takes 10 or 20 years or longer?
IPCC’s blockbuster report on climate science released today, largely ignores the possibility – however small – that the warming slow down might continue for a while. This is a risk that may backfire on its credibility if rapid warming doesn’t resume.
To be sure, the report was forthright about the fact the rate of surface warming has slowed over the last 10-15 years.
“…the rate of warming over the past 15 years (1998–2012; 0.05 [–0.05 to +0.15] °C per which begins with a strong El Niño, is smaller than the rate calculated since 1951,” the report says.
But the IPCC was a little more cryptic about the fact models haven’t predicted the current lull in climate warming.
In its section on the evaluation of climate models, it points out models may have difficulty simulating the course of temperatures over short time periods, but doesn’t directly discuss what’s happening here and now. It merely says:
There are, however, differences between simulated and observed trends over periods as short as 10 to 15 years
Compare that statement to what was in the leaked draft report, in June, which was more direct:
Models do not generally reproduce the observed reduction in surface warming trend over the last 10–15 years
It turns out, models have simulated over four times as much warming compared to reality since 1998, according to a recent study in the journal Nature Climate Change, entitled: “Overestimated global warming over the past 20 years.”
In the spirit of transparency and keeping the public’s expectations in check, the IPCC might have wanted to simply say something to the effect of (but in much more scientific language)…
Global surface temperatures in the last 10-15 years have not warmed as fast as models projected. The possible reasons for this are x, y, and/or z. It is likely temperatures will resume warming at a faster clip, but if x,y, and/or z continue, it is possible this warming may be further delayed and the models will have been wrong and require recalibrating.
To use an analogy, if I’ve predicted a snow storm of 6-12 inches based on computer models and it snows 1-2 inches and then tapers to flurries – I’m nervous and the public, understandably, is beginning to question my forecast. At that point I have two choices:
1) I can stubbornly stick with my forecast. In my reporting, I’d remain silent on the fact it’s barely snowing precisely at the time I had called for a raging blizzard – banking on the fact it will snow like crazy any moment. (I’ve been there, done that, been wrong, and felt the pain.)
2) I can calmly explain why the snow has faded, why the models I relied on failed to show this, and then lay out the full suite of possibilities for the rest of the storm.
Taking the first approach may work the majority of the time, but the second approach is safer, more scientific and has a much lower risk of backlash.