trillionthtonne

This week I managed to stay a bit closer to home and met up for lunch with Dr. Myles Allen of the Department of Physics (Atmospheric, Oceanic and Planetary Physics) at the University of Oxford.

Although we have probably all understood the bit about the “area under the curve” when it comes to CO2 emissions, Myles and his team have brought a whole new dimension to the issue with a recent article in Nature. The core of the arguement is that simply emitting carbon dioxide slower will not address the  issue of climate change unless it involves phasing out carbon dioxide emissions altogether, before we reach an upper limit of one trillion tonnes of carbon.

According to Myles the risk of exceeding the EU stated target of 2 degrees Celcius is primarily determined by the accumulation of carbon dioxide emissions over time, not by short-term emission rates. He has shown that total cumulative emissions of one trillion tonnes of carbon (1 Tt C, or 3,670 billion tonnes of carbon dioxide) over the entire ‘anthropocene’ period 1750-2500 causes a most likely peak warming of 2 degrees Celsius above pre-industrial temperatures. Of this budget, emissions to 2009 have already consumed approximately half (0.5 Tt C).

You can track the “progress” (hardly seems the right word for this) of global carbon emissions on his website. As of today 532 billion tonnes of the trillion tonne budget have been consumed. Extrapolating emission rates forward leads to the forecast that the trillionth tonne will be emitted sometime in the late first quarter of 2045 (although the website shows this moving forward all the time). All this means we have 468 billion tonnes left – which might sound alot, but carve that up amongst 200 countries with populations ranging form 1.4 billion down to a few thousand and it presents quite a problem.

The EU and the USA are already in the process of carving their bit out. Have a look in Waxman-Markey and add up the number of allowances to be issued into the US economy between 2012 and 2100 (from 2050 onwards one billion tonnes of CO2 per annum are allowed) and it comes to 50 billion tonnes of carbon (which doesn’t even account for the whole economy, but most of it). This represents nearly 11% of the total remaining carbon emissions for some 5% of the global population.

Whilst this is a huge reduction from current US emissions (which, according to the IEA, account for some 20% of global energy related CO2 emissions), it of course raises the difficult question of equity. Add to this the fact that US and EU economies will be able to emit more as they purchase offsets from other countries. This in turn raises the issue as to the nature of offsets. In order to keep this system whole all offsets should really only be sequestration based – i.e. a tonne stored away for every tonne emitted. That means forestry and carbon capture and storage and that’s all, although GHG destruction should probably also qualify. By 2050 of course we may also be talking about a tonne removed from the atmosphere, but that will still have to be sequestered somewhere as well. There is a certain irony here in that neither forestry nor CCS qualify as offsets under the EU-ETS today – in the case of forestry it is because the EU doesn’t want to allow it and in the case of CCS because the international community won’t allow it to qualify under the CDM.

Another aspect to all of this is that very long tails of low emissions can’t be allowed. Waxman-Markey does an excellent job of driving down US emissions to very low levels by 2050, but then has a billion tonnes of CO2 remaining indefinately, i.e. a very long tail. Over time that continues to accumulate which just adds to the problem. As I have noted in a previous posting, the last 20% is indeed problematic, but under a trillion tonne scenario it cannot be. As it will be extraordinarily difficult for an economy to get to zero emissions, the solution will doubtless be net zero emissions, which could mean sequestering a tonne of CO2 from the atmosphere for every tonne emitted, either by direct removal or by gasification of biomass to produce electricity with the resultant CO2 being stored.

This will indeed be a brave new world.