Saving the trillionth tonne

In a week that sees the final round of preliminary talks on a new UN climate treaty, where delegates seem to be focusing on emissions in 2020. Myles Allen argues that they must not lose sight of the much greater challenges that lie beyond 2020 or they risk wasting another decade in the battle against dangerous climate change.

On Thursday, 22 October 2009, a single tonne of anthracite coal was unveiled in the Science Museum in London as part of a new exhibition on climate change. Not, you might think, anything particularly remarkable about that, except that this is not any old tonne of coal: it will be, as close as we can estimate it, the trillionth tonne of carbon to be released into the atmosphere as carbon dioxide since industrialisation began in the 18th Century.

The Science Museum, London, and University of Oxford are committed to looking after it for as long as it takes, and solemnly escorting it down to a power station or wherever it can be used most efficiently when total carbon emissions from human activity reach one trillion tonnes.

If, that is, that time ever comes.

The trillionth tonne matters because carbon dioxide accumulates in the atmosphere. Once released, it continues to influence the climate more or less indefinitely unless active measures are taken to scrub it out again, which is not something anyone knows how to do on any scale. Over the past couple of decades, carbon dioxide emissions from fossil fuels have risen by an average of 1.6% per year

Emissions since 1750 comprise of just over half a trillion tonnes of carbon (you can keep track of the number, and the countdown to the release of the trillionth tonne, on the trillionthtonne.org website). This is estimated to have caused just under 1C (1.8F) of global warming (other things affect global temperature as well but, as it happens, their effects more-or-less cancel out over this period). So if we release another 500 billion tonnes, we commit the Earth to a most likely warming of about 2C, which is widely regarded as the threshold for dangerous climate change, and a rubicon that governments of G8 countries and other major economies pledged this year not to cross.

Over the past couple of decades, carbon dioxide emissions from fossil fuels have risen by an average of 1.6% per year, even allowing for the occasional blip like the collapse of the Soviet Union and this year’s recession. Emissions from deforestation have continued steadily.

If these trends continue, which is a relatively conservative “business-as-usual” scenario, we will release the trillionth tonne sometime in the 2040s – a date that is steadily advancing, as the underlying trend is for faster growth in recent years. Emissions resulting from human activity are expected, on balance, to add to the warming effect of carbon dioxide in the future, so if we are to keep the overall warming to less than 2C (or, for that matter, retain any hope of carbon dioxide levels eventually recovering back down to 350 parts per million, or avoid dangerous levels of ocean acidity), we cannot afford to release the trillionth tonne, ever.

What can you do?

Clearly, reducing your carbon footprint helps. Emitting carbon more slowly buys time, which we will certainly need. But to solve the problem in the long term, we need to reduce net emissions, in effect, to zero. Campaigners say atmospheric carbon must not pass 350 parts per million You can’t do this on your own, no matter how heroic a consumer you are. You could reduce your lifetime carbon footprint to zero – by making your home zero-carbon, never use a car and grow your own food – and save the world from dangerous climate change for just a mere two seconds.

So the most important thing you can do is make sure your government recognises the importance of cumulative carbon dioxide emissions in climate policy. At a previous round of negotiations, in Bonn in June, a group of us presented an open letter to the negotiators urging them to acknowledge the need to limit cumulative emissions of carbon dioxide. We did not call for a specific cap: just an acknowledgement that the principle would fundamentally alter the focus of future negotiations. The aim would no longer be to ration out emissions; the aim would be to ban them, just as we banned CFCs. We didn’t save the ozone layer by rationing deodorant. As far as we can tell, that request fell on deaf ears: “This was not the focus of the negotiations at present.” Odd, when cumulative emissions of carbon dioxide are the principal determinant of the risk of dangerous long-term human-induced climate change.

And next time you are in London, drop in to the Science Museum to pay your respects to the trillionth tonne.

Please read the full article here: BBC.co.uk

Image from same source: BBC.co.uk