A FAREWELL TO ICE - POLAR FEEDBACKS AND THEIR IMPACT ON THE GLOBAL CLIMATE SYSTEM
We are all aware of the rapidity with which Arctic sea ice is retreating, a product of the Arctic amplification of global warming, whereby the Arctic is warming about 3 times as fast as lower latitudes. The rapid loss of ice volume (now, in summer, only a quarter of what it was 40 years ago) is causing positive feedbacks which enhance the rates of several other undesirable processes on a global scale. I discuss the main elements. They include:
- Albedo feedback in ice and snow - as the ice retreats it exposes a greater area of open water which has an albedo of less than 10% compared to 80-90% for fresh snow. The same applies to the retreat of snow on land. The result is an enhancement of global warming such that this feedback adds 40% to the excess radiation flux due to greenhouse gas emission alone.
- Sea level rate enhancement- Open water in the Arctic warms the summer atmosphere and causes positive temperatures over the Greenland ice cap which enhance the deposition of meltwater into the ocean and hence the rate of global sea level rise.
- Methane emission feedback - the shallow continental shelves of the Arctic are now free of ice in summer and the water warms up, thawing the protective layer of seabed permafrost and allowing large plumes of methane hitherto trapped in sediment to escape. If carried to completion, this could cause an impulsive jump in global temperatures of order 1degC.
- Weakening of the Atlantic thermohaline circulation . This occurs due to loss of ocean convection in high latitudes. It leads to weaker currents in the N Atlantic, slowing the warming of W Europe but leading to warmer water in the tropical Atlantic and thus more powerful hurricanes.
- Extreme weather events. These seem to be associated with weakening of the jet stream, a consequence of the anomalous warming of the Arctic. They will become more frequent and negatively impact crop production
I conclude that given the increasing rate of warming processes it is hopeless for us to expect to stop or even slow global warming by reduction in our CO2 emissions. Our best hope is to institute a world wide system of direct air capture of CO2, to bring CO2 levels back towards pre-industrial.
Prof Peter Wadhams, University of Cambridge
Prof Wadhams is best known for his work on sea ice. He is currently professor of Ocean Physics, and Head of the Polar Ocean Physics Group at University of Cambridge.
This promises to be an amazing talk from one of the world leading experts on the subject.
Lectures held at 6.30pm, Institute of Physics, 37 Caledonian Road, Kings Cross, London, N1 9BU. Refreshments are served from 6pm on the day of the lecture.
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