World’s carbon budget is shrinking, might run out in six years for 1.5 C

A new estimate by a team of climate experts reveals that the global “carbon budget” – the permissible volume of greenhouse gas emissions that won’t raise global temperatures beyond 1.5 degrees Celsius – has diminished by one-third. Given the current rate of emissions, the world only has a six-year window before it surpasses this critical temperature threshold.

The research determined that to maintain a 50% likelihood of restricting global warming to 1.5°C, the remaining carbon budget (RCB) would need to be approximately 250 GtCO2 as of January 2023. This number is tantamount to the global CO2 emissions over a span of six years at the current rate. On the other hand, for an equal chance of limiting the temperature rise to 2°C, the RCB is estimated to be roughly 1,200 GtCO2. 

The calculation supports a bleak view; many scientists have already accepted that we are not reducing pollution quickly enough to keep global warming under 1.5 degrees Celsius. Due to human actions, the average world temperature has already gone up about 1.2 degrees Celsius compared to before the industrial era.

Earlier, scientists said in 2021 that we could continue emitting at today’s pace for about 11 more years before we would probably run past 1.5 degrees. The window seems to have narrowed down as per this latest calculation with only 6 years remaining now. 

“Our estimate is consistent with an assessment published by 50 leading climate scientists in June and updated with new climate data of many of the key figures reported by the Intergovernmental Panel on Climate Change (IPCC) in August 2021,” authors of the study said. 

The authors further said, explaining the calculation process that led to the finding, “We revised the remaining carbon budget down from the 500 gigatonnes reported by the IPCC from the start of 2020. Some of this revision is merely timing: three years and 120 gigatonnes of CO₂ emissions later, the world is closer to the 1.5°C threshold. Improvements we made to the method for calculating budget adjustments shrank the remaining budget further.”

What is RCB?

The “remaining carbon budget” refers to the total amount of CO2 emissions that can still be released into the atmosphere, while limiting global warming to a level deemed safe by climate scientists, like 1.5 or 2 degrees Celsius above pre-industrial levels. 

The remaining carbon budget takes into account all human-made CO2 emissions, including those from burning fossil fuels (coal, oil, and natural gas), deforestation, and other industrial processes. Once this budget is spent, our CO2 emissions would need to drop to ‘net zero’ to prevent further dangerous warming. 

It’s important to understand that this number is continually depleted with every ton of CO2 we emit, and it’s estimated to be quite limited if we want to hit ambitious targets. This is one of the reasons urgent action on climate change is emphasised.

Reduction in Air Pollution might be the unlikely catalyst  

The reason for the estimation of a smaller carbon budget than previously calculated is related to air pollution. When fossil fuels are burned for energy, they release carbon dioxide as well as small particles like soot and sulphates. These particles not only harm human health but also have a cooling effect on the atmosphere by blocking solar radiation.

The new estimates took into account a better understanding of the extent of this cooling effect. As a result, it was found that reduction in air pollution in the future would remove this cooling influence to a greater extent. While this is beneficial for human health, it is not good for global warming.

Other concerns 

The experts associated with the study, however, said that they are not absolutely sure about many aspects tied to the estimation of the carbon budget. Future emissions scenarios of non-CO₂ pollutants balance can greatly impact the remaining carbon budget as much as varying interpretations on climate response.

The experts also expressed concerns about whether attaining net zero CO₂ emissions will completely halt global warming. Although climate model evidence generally predicts cessation, some models depict prolonged warming for years, even after achieving net zero. If such continued warming occurs, the budget would be even more reduced, they said. 

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References:

https://www.nature.com/articles/s41558-023-01848-5

https://theconversation.com/carbon-budget-for-1-5-c-will-run-out-in-six-years-at-current-emissions-levels-new-research-216459