We recently witnessed a new Greenland melting record. And according to a new paleoclimate comparison by James Hansen we could be in for meters of sea level rise within this century, due to expected non-linearity of the melting process.
The environmental groups around Hansen now call for an 80 percent reduction path towards 2020 – among others for the US and China – to drastically limit our overshoot and get on track to -finally- get back to 350 ppm, hopefully before the Greenland and Antarctic tipping points have been passed.
Considering the suggested urgency taking an additional look at the limited geoengineering arsenal only seems logical. Rational thinking then also dictates us to acknowledge there is very much science does not know about the effectiveness and risks of proposed geoengineering measures on a global scale – but even more when it comes to local effects.
Albedo geoengineering measures are likely to be most effective around the tropics, as solar intensity is highest there. Local ‘solar radiation management’ (SRM), such as cloud seeding, could however have a disturbing effect on the general atmospheric circulation. If albedo measures are carried out in the tropics, it is to be expected that Earth’s total hydrological cycle would decline – as tropical evaporation would be lowered. Also, the cooling effect would be smaller towards the poles – where it may be most needed.
We found a paper at Environmental Research Letters from November 2009 looking into the matter, with researchers of the University of Bristol and the British Antarctic Survey, investigating the possible ‘fate of the Greenland ice sheet in a geoengineered world’ (PDF).
The researchers combine a global climate model and an ice sheet model and conclude partial SRM policy would suffice and Greenland melting could be halted by stabilising temperatures above pre-industrial levels.
It is a bit of a strange conclusion. Less snowfall and higher temperatures combined would always lead to melting, one would assume. The model suggests however that precipitation over Greenland would increase somewhat and compensate for some residual warming – in a submaximally geoengineered world with 4 times historic CO2 levels.
We are quite confident Hansen would disagree with the model’s outcome anyway. That is because the current ice sheet models don’t represent the sudden dramatic melting that the world witnessed previously in the Pleistocene. And a less than 1 degree warmer atmosphere in the Eemian had a 5 meter higher sea surface globally.
But to be safe even Hansen might consider adding a little SRM to his drastic emissions reduction path.
© Rolf Schuttenhelm | www.bitsofscience.org