532,151,027,622: that’s the amount of carbon in tonnes that we’ve released into the atmosphere over the past 250 years from burning coal, making cement and chopping down forests, according to the calculations of Oxford University researchers.
You can watch this number climb rapidly on the newly launched website, trillionthtonne.org. Hosted by the Oxford e-Research Centre, it shows in real time just how close we are to reaching one trillion tonnes of cumulative carbon dioxide emissions, the maximum level allowable if we are to limit warming to less than 2 degrees Celsius.
The concept of restricting cumulative emissions to one trillion tonnes comes from work by Oxford climatologist Myles Allen and collaborators, who, in April this year, published two seminal papers in Nature [subscription]. They also wrote a commentary in Nature Reports Climate Change [free access] at the time, explaining the policy implications of their work: essentially, their point is that we need an overall carbon budget, as well as short term emissions targets. That’s because CO2 hangs around in the atmosphere for millennia, which means that peak warming is determined by cumulative emissions, rather than by the rate at which CO2 is emitted over the short-term.
Though a trillion tonnes may sound like rather a lot, the fact that we’re more than half way there is alarming. Unless we start to reduce emissions rapidly, we’ll have released the trillionth tonne by 2045, shows the counter on the website. And we could go way beyond a trillion tonnes by the second half of this century, unless we mitigate, because there are several trillion tonnes of carbon available in fossil fuel reserves.
To make matters worse, the researchers estimate that to have less than a one-in-four chance of global warming exceeding 2°C, we may well need to keep our cumulative emissions to 750,000,000. The challenge is large: emissions will need to start to fall between 2 and 4.5 percent per year immediately and indefinitely if we are to avoid dangerous warming, according to these estimates.
The website was launched on October 22 to coincide with the unveiling at London’s Science Museum of a one tonne heap of anthracite coal, representing the trillionth tonne of carbon to be released into the atmosphere.