Many newspapers have pointed out the fact that the surface temperature of the earth has not changed markedly over the last 15 years. And in turn some seem to think that because of this climate change is not happening.
Although there is more to climate change than the surface temperature of the earth let us first look at the that claim. After some time spent websearching I found NASA’s downloadable global dataset of land and (surface) ocean temperatures (actually, temperature anomalies — the difference between temperatures and a baseline average). This dataset contains monthly and yearly anomaly data back to 1880. Links to the methodology for calculating the global summary data are here.
When I first looked at the data I immediately applied a least squares linear regression on the temperatures between 1998 and 2012. Rather to my surprise the regression is not flat as I had assumed the claim was. It is not nearly as steep as the regression from 1990 to 1999, but the yearly change is about the same as the change between 1880 and 2012.
|Years||Temperature increase (slope of linear regression)|
So what is it that hasn’t changed? Perhaps they mean the average temperature of the earth? And indeed, 1998 was (up until then) the hottest year on record, the average temperature of the following 15 years is less than the average temperature of that year alone. Well, you sort of expect that if you pick an exceptionally hot year as your baseline. On the other hand there have been 4 years hotter than it since then.
So as far as I can tell, the surface of the world continues to warm, just not as rapidly as it did in the 90s.
But why isn’t the earth warming as fast as it was? More greenhouse gasses are in the atmosphere, one would expect more heat to be trapped on the earth. The answer appears to be that in recent years more of the heat is going into warming up the deep water of the ocean and less into warming the surface. Indeed when this deep water warming is taken into account the heat transfer to the earth as a whole can be seen to be accelerating (Nuccitelli et al).
But climate change is not restricted to temperatures. The ice caps are melting, there are more droughts in our wheat-belts, more fires in areas with Mediterranean climates (who can forget that in SB there were three major fires in the 12 months from July 2008 to June 2009), more and more powerful hurricanes in the Atlantic, more flooding… Recently there have been a number of papers showing that individual storms, droughts, etc. are outside the range of historical variation.
The last time the CO₂ in the atmosphere was as high as it currently is the surface temperature of earth was about 3°C (5°F) warmer than now with the arctic as much as 8°C (15°F) warmer. Sea level was about 30 feet higher. So that’s probably the steady state condition we will obtain if the CO₂ concentration remains at its current level. We don’t know how long it will take to get there, but that’s what we’re looking at. Of course, the CO₂ concentration is still climbing year after year so as things now stand the steady-state condition will probably be even warmer — MIT estimates that by 2100 the CO₂ concentration will be about 900ppm with global temperatures rising to about 10°F higher (and Arctic temps ~20°F higher).
The climate has changed. The climate is changing. The climate will change, probably catastrophically. We just don’t know how long it will take or how far it will go…