Notwithstanding the efforts of scientists like Kevin Trenberth to make us believe otherwise, impacts of climate change to date are very difficult to discern. Although temperatures today average about 1C more than they did in 1850, it hasn’t changed the number or intensity of storms, droughts and probably not for floods. We are not inundated by either sea level rise or climate refugees. As temperatures have climbed, so have agricultural yields. However, the number and intensity of conflicts have gone way down.
A minor debate occurring now in the climate blogosphere is tangentially related to this. Roger Harrabin, writing in the BBC, quotes Richard Tol as saying “Most people would argue that slight warming is probably beneficial for human welfare on net, if you measure it in dollars, but more pronounced warming is probably a net negative.” In this, Tol is merely echoing the IPCC–or quoting himself, as he was a lead author for the IPCC’s section on the subject.
The question is when do the benefits of warmer climate begin to be outweighed by negative impacts? Harrabin and Tol go back and forth on this, and have gone back and forth since the story’s publication in the climate blogosphere.
As near as I can tell, what Tol is arguing is that a warming climate shows net benefits up to 1C temperature rise–what we have now. He believes that the negative impacts of climate change will clearly outweigh those positives when it gets to 2C temperature rise. This leaves a grey area between the two levels–and given the state of the science, that seems reasonable.
In fact it would be reasonable, given what temperatures have done since 1945 (when human contributions of CO2 are held to have begun on a large scale) that there will be periods of time between the realization of 1C and before we hit 2C that will be benign, and periods of time that will see sharp negative impacts.
A more germane question might be ‘How long a period will we see between a 1C temperature rise and a 2C temperature rise?’
As Tol accepts the IPCC mid-range estimate of 3C, he thinks it will be relatively early in the century. As a Lukewarmer with a more modest view of sensitivity (I think it will be about 2.1C), I think we have a little more time.
But because my calculations show energy consumption (and fossil fuel usage) rising much more than do the International Energy Agency, British Petroleum, the World Bank, the IMF and the Department of Energy’s Energy Information Administration (gulp–that’s a lot of smart people I’m disagreeing with), the grace period won’t be as long as we would all like.
I think the worm turns in 2075. At which point what Kevin Trenberth is saying will become cogent and salient. Which is why I wish he and others would quit crying wolf.
Because I believe the wolf will come. The next 60 years are essentially the calm before the storm.