mt has a a transcript of the Copenhagen closing plenary. Let’s have a look. Better still, go read it yourself. I’m not going to cover it all.
Our conclusion is that recent observations confirm that, given high rates of observed emissions, the worst-case IPCC scenario trajectories (or even worse) are being realised. For many key parameters, the climate system is already moving beyond the patterns of natural variability within which our society and economy have developed and thrived. These parameters include global mean surface temperature, sea-level rise, ocean and ice sheet dynamics, ocean acidification, and extreme climatic events. There is a significant risk that many of the trends will accelerate, leading to an increasing risk of abrupt or irreversible climatic shifts.
My first thought is that this is somewhat ambiguous – do they mean that what is happening *now* is worse, or do they mean that what we now think likely to happen in the future is worse? Or both? My second, is that banking on high emissions from 2008 continuing into the future is dubious – the economic downturn will cure that, at least briefly. Anyway, enough of my quibbles: what did Stephan Rahmstorf make of it, you probably care more about his opinion than mine.
First of all, not everything is worse than expected. So that’s the good news. The global temperature is actually rising just as expected… But there are other components of the climate system that we don’t understand that well for example the sea ice behavior, the continental ice sheet behavior, the sea level, and unfortunately, in these components, where we don’t understand them so well that we can confidently compute them, things seem to go faster and worse than we had expected so far. For example the shrinking arctic sea ice is actually declining much faster than in any of the climate models, and we also sea that sea level over the last 20 years or so is rising about 50% faster than the climate models have projected. Another reason for concern is that if you look at the history of this planet, climate changes – the natural climate changes in Earth’s history, we find that past warm climates were significantly underestimated by models, for example the Pliocene.. And we also find that climate changes in earth’s history often have been very abrupt, that’s another thing that we can’t quite reproduce in the models, and at this conference I’ve seen some interesting evidence as to why some aspects of the climate in the climate models may be systematically too stable, so that in the real world things might actually be more unstable than in our models.
So I think SR is backing off from the conference statement somewhat: their first key parameter – global T – isn’t off on the worst case scenario; it is where we expect. Other more poorly understood components are worse? Maybe. If 2009 is worse for Arctic sea ice than 2007, I’ll concede this point to some extent. As to misestimating past climates, I’m not sure how much that matters – in many cases, we don’t really know what the climate was then anyway. The bit about stability is interesting; would be nice to know more.
Stern: he still hasn’t understood (or more likely read, alas) what mt had to say about lawnmowers (but don’t count on the military to save you. They won’t). And I don’t believe this “we can solve GW with 1-2 percent of GDP stuff”.
Dan Kammen: why aren’t you silly industrial people doing the right thing? You must be so stupid. It is so frustrating, we keep telling you what to do but you don’t do it!
Danish PM: mt thinks he is spot on, I find it hard to agree. He has nothing intersting to say about climate, so it is the econ/pol that is relevant. He appears to take Stern at face value. Probably hard not to, when Stern is sitting next to him, but he must be aware that Stern’snumbers are dubious (me or or me quoting Nordhaus). The European Union has committed to 30% reductions by 2020 as part of a global agreement – sounds great, but there isn’t a lot of sign of that coming to pass.
The bit near the end – about 9/10 of the way down – about different ways of looking at 2 oC target is interesting, to see how confusing it can all get. Among people who have in theory just finished listening to it being very carefully expalined to them.
