C A R B ON B U D G E T

Making accurate predictions about carbon emissions, global warming and subsequent climate change is far from simple given the number of unpredictable variables in the pot. But without predictions, climate scientists cannot persuade governments of the urgent need to make rapid and deep cuts in carbon emissions. Enter CARBON BUDGETS.

Humans on planet Earth have a Current Remaining Carbon Budget (CRCB) - that is the amount of CO2 expressed in Gigatonnes (Gt) that, if emitted in the future, will result in our failure to keep global temperature increase below 1.5 °C. In other words, 'spending' that budget will result in the failure to meet the 2015 Paris Climate Accord whose goal was to pursue efforts “to limit the temperature increase to 1.5°C above pre-industrial levels.”

So what is our Current Remaining Carbon Budget? How much do we have left and how quickly is it being used up?

The concensus among climate scientists* is that we have around 200Gt of CO2 emissions in the budget. If we keep our emissions to below that mark, there is an 50% chance of keeping temperature increase below 1.5°C. At our current 'spend' rate of 40Gt per year, then by 2030 at the latest, the 200Gt will have been released into the atmosphere and the chances of meeting the Paris Accord become slim. Put bluntly, given that we are still 75 years away from the end of this century, the 1.5°C target is pretty much dead. It was, after all, exceeded in 2024 and while one swallow doesn't make a summer, it's a powerful indicator that by 2030, 2024-like conditions will become the norm.

What about 2°C? After all, in 2015, 196 countries adopted the legally binding treaty which aimed to hold “the increase in the global average temperature to well below 2°C above pre-industrial levels". This was not about 'pursuing efforts' - a rather vague target. Instead, this was about ensuring that global warming never got close to 2°C. For a 50% chance of 2 °C the Remaining Carbon Budget is around 1,100 Gt of CO2. Once again, assuming annual emissions of CO2 of 40Gt, then it is expected that this budget will be spent in 27 years from now around 2052. That doesn't necessarily mean on that specific year, temperatures will cross the +2°C line. There will be years before then and shortly after when Earth's average temperature exceeds 15.7°C (pre-industrial temp = 13.7°C). From 2052, anything less than 15.7°C will become less and less frequent.

Anything over +2°C will be catastrophic for countless millions of Earth's inhabitants. That includes all 10 million species, not just Homo sapiens. These CRCB predictions are not dressed up in endless climate terminology with an array of 'ifs' and 'buts'. They are brutally clear. If governments of the developed world don't introduce savage cuts to their carbon emissions in the next 5 years, then +2°C is a certainty around 2050.

*The figures above are based specifically on a paper in Nature Climate Change: Lamboll, R.D., Nicholls, Z.R.J., Smith, C.J. et al. Assessing the size and uncertainty of remaining carbon budgets.