Friday, June 02, 2006

This is a dumb way to add a photo

You would think that a company dedicated to hosting blogs would allow you to put a picture up without first posting it as an entry... If you did think that then you would be wrong.

Global warming: What do we expect?

It is widely agreed that global CO2 concentrations are increasing. There are complicated models that enable climate scientists to try and predict the effect that these rising concentrations will have on the global climate. However, to get an idea for what one might naively expect, I have found it useful to imagine a world without any greenhouse gases.

Global CO2 concentrations have historically been approximately 280 ppm (parts per million). This concentration of CO2 leads to the temperatures that we have grown accustomed to here on Earth. A simple calculation taking into account the energy flux hitting the Earth from the sun allows one to conclude that in the absence of greenhouse gases the mean surface temperature of the Earth would be around -20C. The presence of greenhouse gases is therefore essential for life on Earth; if there were no greenhouse effect then the Earth would be a giant ball of ice.

Humans are now emitting large amounts of CO2 into the atmosphere, causing the concentration to rise to ~380 ppm. This is a significant increase above historic levels. If 280 ppm were enough CO2 to increase the temperature of the Earth by 40 degrees Celcius, then how much of an increase do we expect from 380 ppm? I would have naively expected temperatures to rise much more than they actually have, which means that the global climate system has a remarkable amount of negative feedback. The question is, how long will this negative feedback continue to operate? Estimates of future CO2 concentrations vary depending upon when the world begins to take the threat seriously, but even relatively optimistic scenarios estimate that CO2 concentrations will not plateau until approximately 750 ppm. This would correspond to an almost tripling of CO2 concentrations. I have no idea what the effect of this would be on global climate. The scary thing is that nobody else does either.