Parliamentary feedback

The Parliamentary Office of Science and Technology (POST) has come to the attention of this blog from time to time, most notably when it was noticed that it was chaired by Lord Oxburgh and included a member of the Russell panel. Lord O has now stood down as chairman and has been replaced by Adam Afriyie MP, but remains on the board.

POST has just issued a briefing on climate feedbacks and this is interesting reading. It was written by a POST staffer, but the research was done by a secondee called Danny Heptinstall, who seems to be an ecology PhD student at the Aberdeen Centre for Environmental Sustainability (and whose secondment is being paid for by the British Ecological Society). Hmm.

The document is structured so as to consider physical feedbacks separately from carbon cycle feedbacks, but the coverage of the specifics is rather odd. Under physical feedbacks we learn about water vapour and albedo, but there is no mention of clouds. We are, however, told that "The underlying physics of physical climate feedbacks are relatively well understood so they are comparatively well represented in models". Blimey.

It's only in the later section on uncertainties that we learn that there is a cloud feedback, and here there is mercifully a suggestion that there are still some unknowns to consider.

Cloud Feedback
Clouds can both warm and cool the climate and the sum of these effects determines whether clouds result in a net cooling or warming effect. Both high and low clouds reflect the sun’s radiation back into space, causing the Earth to cool, and trap heat, preventing it from being lost into space. Low clouds trap less heat than they reflect so they have a cooling effect on the climate, while high clouds trap more heat than they reflect so they have a warming effect.

Although the cooling and warming properties of different clouds are well understood, there is uncertainty about how climate change will influence the height of clouds. Most models suggest the feedback will be amplifying as the height of clouds will increase in a warmer world. However, some models predict the feedback will have little overall amplifying effect. No models predict the cloud feedback to be net diminishing.

And here are the conclusions:

Compared to existing model estimates, it is likely that climate feedbacks will result in additional carbon in the atmosphere and additional warming. This is because the majority of poorly represented climate feedbacks are likely to be amplifying feedbacks. This additional atmospheric carbon from climate feedbacks could make it more difficult to avoid a greater than 2˚C rise in global temperatures without additional reductions in greenhouse gas emissions. The strength of many amplifying feedbacks is likely to increase with warming, which could increase the risk of the climate changing state (Box 3). Some commentators suggest the uncertainties in our knowledge of carbon cycle and physical feedbacks may mean the Earth will warm faster than models currently estimate.

Comments

[HaroldW]

NickM --
Yes, that sounds better to me...a "w" shape in which the well-depths are modulated over time by the orbital variations. AGW would be thought of as excavating the warm (right-hand) side of the interglacial (right) well, thereby moving the location of the minimum to the right.