The reason we keep getting double-six
Dr James Hansen had an Op-Ed published in the Washington Post newspaper last Saturday – under the title: ‘Climate change is here – and worse than we thought’. In it he mentions a paper, which was published yesterday (6 Aug 2012) in the weekly Proceedings of the National Academy of Sciences (PNAS) magazine. For those without a subscription, a brief précis of the paper is also available on the Columbia University website.
Having emailed Dr James Hansen and pleaded poverty through unemployment, he has taken pity on me and provided me with a PDF copy of the final proof of the article (as approved by him for publication). For this, I am – and will remain- extremely grateful. However, in what follows, so as not to be seen to be taking liberties or risk breaching copyright, I will quote mainly from the Washington Post and Columbia University pieces (rather than the PNAS).
As many others have noted, Hansen has a wonderfully down-to-earth way of communicating complex ideas; and his writing often displays a conversational style. He opens his Op-Ed by reminding readers of another very warm summer – 1988 – when he first testified before US Senate about the consequences of humanity’s unabated burning of fossil fuels, to which he now adds bluntly… “I have a confession to make: I was too optimistic.”
It was in 1988 that Hansen first introduced the concept of climate dice, to try and help people understand his message: That the change then expected (and now observed) is not the result of natural variability, because the burning of fossil fuels is changing the nature of what is normal. In effect, Hansen was suggesting that normal climate dice would have two sides with a one (representing cooler-than-normal weather); two sides with a three (representing normal weather); and two sides with a six (representing warmer-than-normal weather. Rolling the die again and again, or season after season, you would have an equal chance of throwing a one or a three or a six.
However, by upsetting the dynamic equilibrium of our atmosphere by adding CO2 from previously-fossilised carbon, we have now loaded the climate dice so that now only one side is cooler than normal, one side average, and four sides warmer than normal. Even now, we may get the occasional cooler-than-normal summers or a typically cold winter; but the chances of weather being warmer than (what was previously) normal are now much greater.
In summarising this newly-published analysis of six decades of global temperatures (co-authored with Makito Sato and Reto Ruedy), which concludes that “for the extreme hot weather of the recent past, there is virtually no explanation other than climate change”, Hansen emphasises that this “is not a climate model or a prediction but actual observations of weather events and temperatures that have happened”.
Having looked back over this data (for the northern hemisphere), Hansen et al 2012 finds that extreme hot weather events (greater than 3 standard deviation [+3 StdDev.] warmer than local average) covered 0.1 to 0.2 percent of the Earth’s surface at any one time during the reference period for the study (1951 to 1980). However, while the average temperature has slowly risen over the last three decades, extremely hot weather events now cover 10 percent of the Earth’s surface. This means that, in any given summer, they are between 50 and 100 times more likely to occur than they used to be. Again, this is not a prediction or a model; this is just statistical analysis of weather that has occurred.
Our climate is changing – and we will indeed have to live with it or, if we are unfortunate to be in the wrong place at the wrong time, die because of it. As Hansen et al point out; the heat wave in Europe in 2003 killed 50 thousand people.
The piece on the Columbia University website includes some helpful colour illustrations such as this one (Figure 2) showing temperature anomaly distribution curves.
The frequency of occurrence (vertical axis) of local temperature anomalies in the Northern Hemisphere (NH) relative to the 1951-1980 baseline, in units of local standard deviation (horizontal axis). Image credit: NASA/GISS.
Hansen et al describe this increase in the frequency of extremely hot weather events as “the emergence of a subset of the hot category” defined as anomalies exceeding +3 StdDev.. Included among these events are the heat wave and drought in Oklahoma, Texas and Mexico in 2011; and a larger region encompassing much of the Middle East, Western Asia and Eastern Europe (including Moscow) in 2010.
Hansen et al conclude that widespread reluctance to attribute these events to anthropogenic climate disruption (ACD) is no longer justified. This is because, as already stated, it is now 50 to 100 times more likely that any given event is indeed attributable to ACD.
Despite all this, as Hansen et al acknowledge, the distribution of seasonal temperature anomalies (Fig. 2) also reveals that a significant portion (about 15 percent) of the anomalies are still negative, corresponding to summer-mean temperatures cooler than the average 1951-1980 climate. Thus, people should not be surprised by the occasional season that is unusually cool. Cool anomalies as extreme as -2 StdDev. still occur, because the anomaly distribution has broadened as well as moved to the right. In other words, as well as getting generally warmer, our climate now encompasses a wider range of extremes.
This is bad news; and saying “it ain’t necessarily so” will not change the probability that it is.