18 september 2013

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Climate change to have double impact - study

by Naffez Ahmed, The Guardian, September 18, 2013

New research shows traditional IPCC models could be underestimating global warming due to feedbacks

As the world awaits the Intergovernmental Panel on Climate Change's (IPCC) latest verdict on the state of the climate, new research out this year finds that climate change could have double the impact previously thought.

The peer-reviewed study published in the Quarterly Journal of the Royal Meteorological Society argues that conventional conclusions on climate sensitivity - the extent to which global temperatures respond to greenhouse gas emissions - underestimate the role of some amplifying feedbacks that may intensify climate impacts in ways that many models tend to overlook.

Traditional estimates of climate sensitivity such as that adopted by the IPCC focus on "fast feedbacks" like water vapour, natural aerosols, clouds, and snow cover, but do not sufficiently account for slower feedbacks including "surface albedo feedbacks from changes in continental ice sheets and vegetation", and climate greenhouse gas feedbacks "from changes in natural (land and ocean) carbon sinks."

These types of feedbacks refer to self-reinforcing process which, once human-induced emissions create a change in a particular eco-system, lead to further changes beyond the initial human forcing as different parts of the system continue to respond. With 'albedo', for instance, the reduction of snow and ice cover due to melting induced by global warming means less surfaces reflecting sunlight back into the atmosphere, and thus more absorption of heat, which leads to further melting - and potentially a self-reinforcing cycle that contributes further to overall warming.

With 'carbon sinks', as the oceans absorb CO2 and excess heat due to global warming, they could reach a saturation point where their ability to absorb is continually reduced, in turn allowing global warming to accelerate - eventually, the oceans themselves could become an increasing source of CO2 if this process continues.

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