‘Carbon budget’ for 1.5 C will run out this decade, says study

In alarming climate change news, scientists have announced we’re running out of time to get to zero carbon emissions almost twice as fast as we thought.

“The remaining carbon budget, the net amount of CO2 humans can still emit without exceeding a chosen global warming limit, is often used to evaluate political action against the goals of the Paris Agreement,” researchers write in a new paper, published in Nature Climate Change.

“We conclude that the remaining carbon budget for a 50% chance of keeping warming to 1.5 °C is around 250 gigatonnes of CO2 as of January 2023, equal to around six years of current CO2 emissions.”

This is half the budget provided by the 2023 IPCC report, which is alarming news for those in the climate space.

“The work by Lamboll and colleagues makes for uncomfortable reading for policymakers, ostensibly halving the best estimate for the remaining carbon budget cited in the 2023 IPCC AR6 from 500 GtCO2 to 250 GtCO2,” said Benjamin M. Sanderson from the Centre for International Climate and Environmental Research in an accompanying editorial.

It’s worth noting that the six-year ‘business as usual’ timeframe doesn’t mean we’ll be at 1.5 degrees on that date, but it does mean that we won’t be able to emit any more carbon without the world repaying us with at least 1.5 degrees of warming in the future.

The researchers also suggested that for a 50 percent change of keeping under 2 degrees of warming, the remaining carbon budget is 1,200 gigatonnes of carbon, leaving 23 years at current levels for our budget to run out.

The journal article uses an updated dataset and methodology to get their new numbers and characterise some of the uncertainty. Most importantly, they highlight aerosols, suggesting that this is masking some of the increase in temperature, and needs to be factored in before the carbon budget can be confirmed.

“The warming we experience today has occurred due to a combination of historical emissions of greenhouse gases and aerosols, together with natural processes (solar cycles and volcanoes) and natural variability,” says Sanderson.

“As such, warming from greenhouse gases today is partially compensated by cooling from aerosols, and the strength of this masking is a key uncertainty.”

While many countries around the world are trying to limit emissions, despite a drop from the COVID-19 pandemic, we are still increasing emissions year on year.

Even if we drastically lowered emissions now, we would still only have until the mid-2030s to completely stop emitting CO2 into our atmosphere to stay within the Paris budget.

“If Lamboll and colleagues are correct, mid-century net-zero targets are insufficient to prevent an overshoot of 1.5 °C,” Sanderson concludes.