A week or two ago a “study” by the World Wildlife Fund got a lot of play in the media. Its key conclusion:
The report says that the 2007 report from the Intergovernmental Panel on Climate Change (IPCC) – a study of global warming by 4,000 scientists from more than 150 countries which alerted the world to the possible consequences of global warming – is now out of date.
WWF’s report, Climate Change: Faster, stronger, sooner, has updated all the scientific data and concluded that global warming is accelerating far beyond the IPCC’s forecasts.
As an example it says the first tipping point may have already been reached in the Arctic where sea ice is disappearing up to 30 years ahead of IPCC predictions and may be gone completely within five years – something that hasn’t occurred for 1m years. This could result in rapid and abrupt climate change rather than the gradual changes forecast by the IPCC.
This is not at all an uncommon meme. If one searches “global warming accelerating” on Google, one gets 1,100,000 hits. The #1 hit says:
I actually believe there is a small upward temperature trend due to CO2, on the order of 0.05 – 0.1C per decade. But it is staggering to me that so many people can insist, with a straight face, that warming is “accelerating” or, crazier, that it is “worse than forecast.”
Let’s take the acceleration first. Here is the recent temperature trend from the UAH satellite data (all the smoothed lines you will see are 36-month moving averages centered on the middle month).
It is possible to argue that there is a warming trend here, but never-the-less it is impossible to see “acceleration,” particularly since 2001. There is an implication in the article that the acceleration has occurred since the last couple of IPCC reports, so let’s zoom into the period since the 3rd and 4th IPCC reports:
No acceleration. Not even any warming (for 8 years! where is that story in the press?)
But how about the proposition that temperatures are rising faster than forecasts? This is patently absurd. We can go back to just about every IPCC and alarmist projection and show that temperatures are well less than forecast, but lets use James Hansen’s forecasts to Congress in 1988 because it gives us 20 years of data to work with (actual data is a blend of Hadley CRUT3 and UAH satellite as discussed here.)
I always get folks who insist that I am making a mistake by using the Hansen A scenario because Hansen at the time described it as extreme. But in fact, world CO2 production has been even greater than the Hansen A scenario. Hansen A underestimates the inputs, and still grossly overestimates the output. The only real discussion one can find on the IPCC forecasts is whether one can argue the actuals are barely poking their nose up into the low end of the forecast confidence intervals or not.
The one piece of evidence most of these folks making the “accelerating” argument use is sea ice extent in the North Pole. The media has been full of stories about disappearing sea ice, and in fact in 2007 the North Pole had the lowest sea ice extent in the last 30 years, though coincidently in the same year the South Pole had the highest sea ice extent in 30 years. But there is a logical fallacy here. The fact that the statement “global warming causes sea ice to retreat” is true does not mean the statement “sea ice retreat means the globe is warming” has to be true. And in fact, we see from the data above, this is not true. It is amazing to me that in the conflict between “thermometers” and “sea ice extent at one pole” as measures for global temperature, sea ice extent seems to trump thermometer readings. Particularly when this sea ice signal only exists at one of the two poles.
There is no question that the Arctic has warmed more than the rest of the planet. In fact, much of the rise in global averages is driven by the Arctic (and all of it is driven by the norther hemisphere above the tropics — the rest of the world has no warming signal over the last 30 years). Below we can see the satellite measurement of the temperature anomaly in the Arctic:
A one degree rise over a couple of decades is indeed substantial. In fact, though, during the last couple of years, we have actually seen either flat temperatures or, perhaps, a cooling trend. Here is a closeup:
So it might be that we should look for other explanations of unusually large sea ice retreats in the summers of 2007 and 2008. It has been suggested by NASA that winds and ocean currents are in part to blame, and by others that black carbon deposits on the ice from Chinese coal plants may also be increasing summer melt.
Whatever the case, there are a lot of good reasons to believe we are not seeing an “acceleration” in global warming. And a lot of very, very good reasons to believe we are not reaching a “tipping point.” Tipping point implies that we have entered a regime where the climate is dominated by runaway positive feedback. I have addressed this topic many times, and will not address it right now, but in short all of the catastrophe in climate models is due not to the assumption of CO2 as a greenhouse gas (which actually tends to yield modest warming in models) but the assumption that the Earth’s climate is dominated by substantial positive feedbacks. I discuss the entire topic of positive feedbacks and climate forecasts in the video below:
Update – if we add glaciers here in addition to sea ice, we see the same slow retreating trend. However, the trend goes back 200 years! That’s 150 years longer than man has been producing substantial CO2 emissions. (source)