Window for stopping global warming above 1.5C 'could run out in six years', study finds

The critical carbon budget required to prevent global temperatures from rising 1.5 degrees Celsius above pre-industrial levels may be exhausted within the next six years, a study has found. Scientists warned that the window of opportunity to attain the key target of the Paris Agreement is 'rapidly closing', and if current emission rates persist, breaching this limit is increasingly likely.

According to the study's findings, there are approximately 250 gigatonnes of carbon dioxide (GtCO2) left to be emitted before locking in a temperature increase of at least 1.5 degrees Celsius. Without substantial and immediate reductions, this budget could be depleted within the next six years, posing a serious threat to climate goals.

The Intergovernmental Panel on Climate Change (IPCC) in 2018 estimated a 50% chance of staying within the 1.5C threshold if global emissions were halved by 2030 and reduced to net zero by 2050. However, the new study, recently published in the Nature Climate Change journal, has updated this assessment by taking into account greenhouse gas emissions over the past five years. It has also factored in recent measures to reduce air pollution, which have had the unintended effect of reducing aerosols in the atmosphere, causing a slight cooling impact on the Earth's average temperature.

Despite the collective commitment to the 1.5°C target at the historic UN climate conference in Paris in 2015, no single country has implemented policies that align with this goal, as reported by Climate Action Tracker. Current estimates from the IPCC, the gold standard of climate science, have the Earth on track for nearly 3C of warming by 2100 with global emissions still increasing in 2023.

Scientists have said 3C would be catastrophic for humans and other forms of life on Earth, with some warning that breaching even the 1.5C limit could set off tipping points such as melting polar glaciers which could cause the planet to heat up independent of human emissions.

Dr Robin Lamboll, of Imperial College London’s Centre for Environmental Policy and lead author of the study, said: “Our finding confirms what we already know – we’re not doing nearly enough to keep warming below 1.5C.

“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.”

There has been a lot of uncertainty in judging how much the world can emit before breaching the target as there are numerous gases that cause warming as well as indirect effects of other pollutants such as the cooling aerosols.

The study authors said they used a new dataset and an improved climate model to give a more accurate estimate of the remaining budget.

Although 2023 is likely to have a global average temperature of above 1.5C and be the hottest year on record, this does not mean the Paris goal is dead as meteorologists measure the average figure taken over many years in order to account for a natural variability in temperature.

Many countries have targets in place to become net zero by around the middle of this century, meaning the amount of emissions put into the atmosphere equals those removed either by nature or technology.

Restored forests, wetlands and oceans may begin to draw more carbon from the atmosphere than is being emitted, cooling the Earth’s temperature, though the precise effect remains largely an educated guess.

Dr Lamboll said: “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 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.”