The amount of carbon dioxide (CO2) emissions that humans can release while still having a chance to limit warming to 1.5°C compared to pre-industrial levels may get exhausted within the next six years, warns a new study. This is half of what the Intergovernmental Panel on Climate Change (IPCC) had previously estimated in its Sixth Assessment Report (AR6-WG1) released in 2021.
The peer-reviewed study led by Imperial College London was published in Nature Climate Change on Monday and provides the latest estimate of the global carbon budget, which the researchers have found to be “far lower than previously estimated".
The Remaining Carbon Budget (RCB) is basically the net quantity of CO2 emission that humans are allowed to emit without overshooting a particular warming threshold. It is also a key parameter for policymakers to plan how fast the world must decarbonise under the 2015 Paris Agreement, which sets the goal of limiting warming to below 2°C, while pursuing efforts to control it to 1.5°C relative to pre-industrial levels.
Calculating the remaining carbon budget has remained a complex and challenging endeavour because of several uncertainties. First, it only takes into account CO2 emissions, while other non-CO2 greenhouse gases and the role of other pollutants are not directly accounted for. Now, the researchers from the Imperial College London have used an updated dataset and improved climate modelling to re-evaluate the existing estimates of the carbon budget.
THE NEW FINDINGS
According to the study, the spike in greenhouse gas emissions due to burning of fossil fuels has led to a rapid decline in the global carbon budget – such that it has halved since 2020.
The IPCC in its Sixth Assessment Report (AR6) Working Group (WGI) had estimated that the world could emit about 500 gigatons (Gt) of CO2 starting January 2020 to still have a 50% chance of limiting warming to 1.5°C. However, as per the latest estimate, this budget has now reduced to less than 250 Gt of CO2, which is now left in the global carbon budget as of January 2023. This is roughly half of the 2020 estimate underscoring the need to urgently bring down emission to Net Zero.
‘Net zero’ refers to achieving an overall balance between global emissions produced and emissions removed from the atmosphere. India has committed to achieving a Net Zero by 2070, while it is 2050 for developed countries such as the United State (US) and United Kingdom (UK).
The researchers warn that at the current rate of emissions, which have increased to about 40 billion Gt/year in 2022, the carbon budget will be exhausted within six years by 2029 and put the world on 1.5°C warming.
WHY IT IS WORRYING
The findings are disconcerting as they leave very little time for countries to decarbonise and reduce emissions to keep warming to below 1.5℃, which is important to control disastrous impacts of climate change. The study highlights that the window for keeping warming to safe levels is rapidly closing and current progress on reducing emissions is not enough.
“Our finding confirms what we already know – we are not doing nearly enough to keep warming below 1.5°C. Every fraction of a degree of warming will make life harder for people and ecosystems. This study is yet another warning from the scientific community. Now it is up to the governments to act," said lead author Dr Robin Lamboll, research fellow at Imperial College London.
Although there are still some uncertainties in the way various parts of the climate system will respond in the years just before Net Zero is achieved, experts say the need for climate action is just as urgent whether the budget runs out in six or 10 years. The findings illustrate that any calculation, no matter how rigorous, is subject to change with revised data and understanding.
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