The research is the most recent and detailed analysis of the global carbon budget. The carbon budget is essentially an estimate of how much carbon dioxide we can emit while still limiting global warming to specific temperature increases.
The Paris Agreement, an international treaty signed by 196 countries, established a goal of capping the global temperature rise to well below 2°C above preindustrial levels. The greater goal is to limit this temperature increase to 1.5°C. Progress on these targets is often measured using the remaining carbon budget.
The Imperial study has discovered that the carbon budget is significantly smaller than prior estimates. The researchers estimate that for a 50% chance of limiting warming to 1.5°C, there are less than 250 gigatons of carbon dioxide left in the global carbon budget.
The experts warn that if carbon dioxide emissions remain at 2022 levels of about 40 billion gigatons per year, the carbon budget will be exhausted by around 2029, committing the world to warming of 1.5°C above preindustrial levels.
This dwindling carbon budget is attributed to two main factors: the relentless rise in global greenhouse gas emissions, primarily from burning fossil fuels, and a refined understanding of the cooling effect of aerosols, which has been decreasing globally.
Dr Robin Lamboll, the study’s lead author, highlighted the severity of the situation. “Our finding confirms what we already know – we’re not doing nearly enough to keep warming below 1.5°C.”
“The remaining budget is now so small that minor changes in our understanding of the world can result in large proportional changes to the budget. However, estimates point to less than a decade of emissions at current levels.”
“The lack of progress on emissions reduction means that we can be ever more certain that the window for keeping warming to safe levels is rapidly closing.”
Dr Joeri Rogelj, a professor of Climate Science & Policy at the Centre for Environmental Policy at Imperial College London, noted that these findings align with the UN Climate Report from 2021.
“That report from 2021 already highlighted that there was a one in three chance that the remaining carbon budget for 1.5°C could be as small as our study now reports,” said Dr. Rogelj.
“This shows the importance of not simply looking at central estimates, but also considering the uncertainty surrounding them.”
For those wondering about the 2°C target, the study estimates the carbon budget for that is around 1,200 gigatons. Without intervention, this budget could be expended by 2046.
While there’s been debate about the precise remaining carbon budget due to various influencing factors, this research is more definitive. The experts used advanced climate modeling to address uncertainties, which means their estimates more reliable.
One of the key takeaways is the concept of net zero, which refers to balancing out emissions produced with those removed from the atmosphere. The study suggests there’s a lot we don’t know about how the climate will react as we approach net zero.
For instance, while factors like melting ice might cause further warming, increased vegetation growth could absorb significant carbon dioxide, leading to a cooling effect.
Dr. Lamboll said these uncertainties further highlight the urgent need to rapidly cut emissions. “At this stage, our best guess is that the opposing warming and cooling will approximately cancel each other out after we reach net zero.”
“However, it’s only when we only when we cut emissions and get closer to net zero that we will be able to see what the longer-term heating and cooling adjustments will look like.”
“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 governments to act.”
The study is published in the journal Nature Climate Change.
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