This past week we've had some "good news" about future climate change based on an analysis published in the journal Science called Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum by Andreas Schmittner, et. al. Here's the abstract, which I shall explain in layman's terms below.
Assessing impacts of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 K (°Centigrade) as best estimate, 2 to 4.5 K as the 66% probability range, and nonzero probabilities for much higher values, the latter implying a small but significant chance of high-impact climate changes that would be difficult to avoid. Here, combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations, we estimate a lower median (2.3 K) and reduced uncertainty (1.7 to 2.6 K 66% probability). Assuming paleoclimatic constraints apply to the future as predicted by our model, these results imply lower probability of imminent extreme climatic change than previously thought.
Pre-industrial levels of CO2 in the atmosphere were approximately 280 ppmv (parts-per-million-by-volume) over the last 10,000 years or so (the Holocene). The standard way for assessing the "sensitivity" of the climate to increased carbon emissions in post-industrial times is to model what might happen if there is a doubling to 560 ppmv. In other words, how much will surface temperatures increase in this case? The best estimate, even from the time the first models were developed in the 1970s, has always been 3°centigrade (C) within a 66% probability range of 2 to 4.5.
This new research suggests that the climate sensitivity is "only" 1.7 to 2.6 C with a 66% probability, and the best estimate within that range is 2.3°C.
CORVALLIS, Ore. – A new study suggests that the rate of global warming from doubling of atmospheric carbon dioxide may be less than the most dire estimates of some previous studies – and, in fact, may be less severe than projected by the Intergovernmental Panel on Climate Change report in 2007...
"Many previous climate sensitivity studies have looked at the past only from 1850 through today, and not fully integrated paleoclimate date, especially on a global scale," said Andreas Schmittner, an Oregon State University researcher and lead author on the Science article. "When you reconstruct sea and land surface temperatures from the peak of the last Ice Age 21,000 years ago – which is referred to as the Last Glacial Maximum – and compare it with climate model simulations of that period, you get a much different picture.
"If these paleoclimatic constraints apply to the future, as predicted by our model, the results imply less probability of extreme climatic change than previously thought," Schmittner added...
Some previous studies have claimed the impacts could be much more severe – as much as 10 degrees or higher with a doubling of CO2 – although these projections come with an acknowledged low probability. Studies based on data going back only to 1850 are affected by large uncertainties in the effects of dust and other small particles in the air that reflect sunlight and can influence clouds, known as "aerosol forcing," or by the absorption of heat by the oceans, the researchers say.
To lower the degree of uncertainty, Schmittner and his colleagues used a climate model with more data and found that there are constraints that preclude very high levels of climate sensitivity.
The researchers compiled land and ocean surface temperature reconstructions from the Last Glacial Maximum and created a global map of those temperatures. During this time, atmospheric CO2 was about a third less than before the Industrial Revolution, and levels of methane and nitrous oxide were much lower. Because much of the northern latitudes were covered in ice and snow, sea levels were lower, the climate was drier (less precipitation), and there was more dust in the air.
This is definitely "good news" if the paleoclimatic constraints found by Schmittner and his colleagues do indeed apply to the future. These results may even put the kabosh on hysterical prognostications emanating from the Jim Hansen/Bill McKibben wing of the environmental movement, although I doubt that they will. Needless to say, if these results hold up, an expected warming of 2.3°C is nothing to celebrate. That's still a huge shift in what amounts to no time at all on the geological timescale. The next most rapid warming we know of was the Paleocene-Eocene Thermal Maximum (PETM) which took place about 56 million years ago, and in which it took 20,000 years to get a 5-6°C rise in surface temperature.
The news, if true, is even better than generally thought because there's a snowball's chance in hell human burning of fossil fuels will culmimate in a doubling of atmospheric CO2. In short, I don't think levels will reach 560 ppmv. I just don't see where all those fossil fuels are going to come from. Even if viable alternatives to fossil fuels miraculously appear, the possibility that global economic (GDP) growth will simply continue year-after-year in the 21st century seems very remote. There are all sorts of contraints on that growth, not just the availability of cheap energy.
Imagine it if you can: if atmospheric CO2 were to grow by 3 ppmv per year, it would still take 56 years to get to 560 ppmv. That takes us to the year 2067. No way, Jose!
And that is the real reason the hysterical prognostications I mentioned above have always been laughable. Those making these dire predictions are employing the standard assumption used by economists, commonly referred to as Business-As-Usual (BAU). In short, these "radical" environmentalists assume that economic growth in the 21st century will (or could) mirror the growth of the 20th century. Not so "radical" after all. See what I mean?
Take this "good news" about future climate with a grain of salt. The path humankind is traveling still ends in disaster long before the year 2067. The Awful Truth is that this disaster is no longer impending. It has already begun. You'll see.
Bonus Video — here's some typical crapola from Bill McKibben (see my comments on this post).