A four degree Celsius rise in average global temperature in the 21st century was put forward some months ago by the World Bank, without any serious scientific argument that I could find, and it has resurfaced in Australia recently, in a book by Peter Christoff of the University of Melbourne (Four Degrees of Global Warming: Australia in a Hot World). I thought it was classic scary stuff, and decided to pass it by. But he is now writing about it on The Conversation, where it is being vehemently defended by the faithful. And of course it had a run on the ABC.
What has to be said about this scare is that it is hard to see how the 4 degrees C can occur. A few years ago those worried about warming pointed to the similar trajectories of atmospheric carbon dioxide accumulation and temperature rise, and told us that these would continue until we did something about carbon dioxide emissions. Now that there has been a halt in temperature globally, they have moved the goalposts, stating that this warming will kick in with a vengeance after 2050. How do they know? Their models tell them so.
As I pointed out recently, someone has calculated that at the present almost imperceptible rate of warming it will take 800 years before we get to 2 degrees Celsius above the present. And of course I don’t seriously suggest such an outcome. What we know of warming in the 150 years since we have had some reliable measuring instruments in at least a few places, is that warming and cooling seem to occur in phases. Maybe CO2 has an influence, but the current stasis tells us that the natural phases or cycles (or whatever makes up natural variability) are powerful enough to mask that effect.
Professor William Happer of Princeton has sent me (and others) an email setting out a straightforward calculation based on IPCC figures, and I thought I’d arrange the argument for those who might find the calculations hard going. The core of the IPCC argument is the formula
required CO2 concentration = C = C0 x 2^(DT/DT2) where C0 is the current concentration (C0= 400 ppm), DT is the temperature rise resulting from concentration C, and DT2 is the (disputed) temperature rise for doubling.
The IPCC is asserting that mean global temperature will increase as carbon dioxide concentrations increase, according to a ‘climate sensitivity’ factor, which it sees as producing a 3 degree increase in average global temperature for a doubling of carbon dioxide.
Happer thinks the climate sensitivity figure is too large, and so do I. But let that pass for the moment. If we accept it, and then ask — what is the level of carbon dioxide that would be needed to produce a 4 degree rise in temperature from today? — the answer we would get, using the IPCC formula, would be 1008 parts per million. Today’s level is around 400 pp, which means we would need to have increased the level of carbon dioxide in the atmosphere by more than 600 ppm.
This has to be fantasy stuff. The level of CO2 goes up at about 2 ppm each year, and the biosphere gratefully accepts as much of it as it can. To get to 1008 ppm, at the present rate, will take more than 300 years.
Most of the recent estimates of ‘climate sensitivity’ hover around the 1 degree Celsius figure (that is, a doubling of CO2 provides a warming increment of around 1 degree C). If we put that value into the equation it will take 3,000 years to get to the required level of carbon dioxide. Those who study the Earth’s fossil fuel reserves doubt that they are large enough, even if we were able to use all of them, to produce such a level of carbon dioxide in the atmosphere.
In short, Christoff’s argument doesn’t make sense. As far as I can understand what he has done, he has simply accepted the possibility of a 4 degree warming, and then gone into warning, doomsday mode: here’s what we must do, and we must do it yesterday, and all of you — yes, you too! — have to take part…
Why do people take this sort of stuff seriously?