So, the G8 have agreed to agree to discuss… Grist does it well. Looking at the document on the Heiligendamm website, you’d be excused for thinking that the USA got exactly what it wanted; no fixed commitment, further talks at Bali, and a USA-hosted conference next year. Conveniently, this means that Mr. Bush can wash his hands of the whole difficult-decision-making thing with no trouble from outside the various state legislatures and congress.

But they made a big deal of the ‘50% cuts in emissions by 2050’, so I thought I’d try some back of the envelope stuff. What sort of target is this?

Assuming no change in policy or emissions direction for the next 5 years at least, to 2012, then a phased reduction from then to a target of around 3.25 GtC in the five years leading up to 2050, I work out that the atmospheric CO2 concentration will be around 450ppm. I am sure this is no coincidence. So; this is the aim; 450 ppm by 2050, then another 50ppm or so by 2100, to 500ppm.

What temperature change does this commit us to? Again, it’s not science, but it looks like we’re talking about a global average temperature increase by 2050 of +0.7-1.0C from present, and +1.0-1.5 by 2100 (assuming a CS of ~3C). That’s alright, isn’t it? that’s not too dangerous, is it? We can make the necessary adaptation to that kind of temperature increase at a manageable cost, surely?

Hum.

The Met Office (link on sidebar) has a nice graphic showing what various Summer maxima will look like in 2057 under such a scenario. Anyone planning to invest in a nice Mediterranean property? Ontario looks nice…

Hansen et. al.’s recent ACP paper is an interesting point of comparison. Or you could look at what Mark Lynas ‘predicts’ for a +2C rise. Going to the IPCC, one could be forgiven for thinking that these are both achievable and desirable targets… if.

If a 2C global rise is not sufficient to permanently destabilise the GIS (remember, Polar amplification would imply a ~4-6C rise there).

If a 2C rise is not sufficient to permanently alter the viability of the rainforest, in particular, the Amazon Basin.

If a 2C rise is not sufficient to cause the kind of water shortages suggested in the UNEP ‘snow and ice’ report, which suggests that 40% of the World’s population will be up a very dry creek if global glacier melt continues at the present rate.

There are several more if’s… (feel free to suggest your own).

In truth, a rise of 2C from pre-industrial temperatures is probably the absolute best we can realistically hope for, all things considered. With the 50% cut baseline, we might just scrape it. But I have a feeling that, without other measures to reduce atmospheric CO2, without extreme measures to protect our forests, without measures to deal with ocean acidification, wildfires, permafrost degradation, biodiversity loss… (another long list…) this will not be sufficient to ensure a manageable/sustainable global political and biological environment for our descendants.

Just a feeling.

Be loved.

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