Window to limit global warming to 1.5°C 'is closing'

If CO2 emissions remain at 2022 levels, the carbon budget will be exhausted in six years, scientists warn

The North Cove in the Antarctic. AP

The window to limit global warming to 1.5°C is closing, research has shown.

A team at Imperial College London issued the warning after analysing the global carbon budget, which calculates how much carbon dioxide can be emitted into the atmosphere while keeping temperature rises within certain limits.

The calculation uses targets set by the Paris Agreement, which aims to limit the increase in global temperatures to well below 2°C above preindustrial levels and pursue efforts to limit it to 1.5°C.

The study, published on Monday in Nature Climate Change, shows that if CO2 emissions remain at 2022 levels of about 40 gigatonnes per year, the carbon budget will be exhausted by about 2029, committing the world to warming of 1.5°C above preindustrial levels.

Robin Lamboll, research fellow at the Centre for Environmental Policy at Imperial College London, told The National the study provides the most up-to-date and comprehensive analysis of the budget, which shows “the window to limit warming to 1.5°C is closing”.

“This is not completely unexpected. We released a paper in June, which also intimated that this was a likely change,” said Dr Lamboll.

“But this paper does a lot more checks and robustness calculations and shows that yes, probably the previous budget was over generous.”

Cop28, which will be held this November in Dubai in a year which is likely to be the hottest on record “by quite a large amount” and will also probably see the highest emissions on record, “presents an opportunity for governments to come up with stronger commitments to make the transition to renewable energy”, said Dr Lamboll.

“Last year we didn’t really see Cop advancing much action in terms of preventing climate change, but more focus on moving money to those who are most affected by it.

“I would hope that we would see that effort continue, but doesn’t detract from the main avenue of simply trying to prevent climate change in the first place. So both are important. But I would imagine, I would hope, that this Cop has more continued support for climate action.

“And that people look at all these records being broken and say gosh, we really need to do more than we are.”

The study also found that if CO2 emissions continue at current levels, the central 2°C budget will be exhausted by 2046.

Dr Lamboll said the study shows the window for a 2°C warming or “well below 2°C” remains open.

“That budget shrank. But it shrank by a smaller amount, both in absolute and in relative terms. So very much not saying the Paris Agreement is dead.

“There is very much opportunity to keep that alive. And it is worth noting that two Cops ago we saw significant movement and we did see more governments coming forth with better climate targets, meaning that actually it’s possible if we optimistically interpret these for projections to indicate below 2°.

“So we have to hope that this Cop has a similar power and once again brings forth new commitments to faster roll-out of renewable energy.”

The new research used an updated data set and improved climate modelling compared to other recent estimates, published in June, characterising these uncertainties and increasing confidence around the remaining carbon budget estimates.

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An aerial shot of the Great Barrier Reef in Australia, showing parts of the reef that has been subjected to coral bleaching.

The new calculations mean the budget is less than previously calculated and has roughly halved since 2020 due to the continued increase of global greenhouse gas emissions, caused primarily from the burning of fossil fuels as well as an improved estimate of the cooling effect of aerosols, which are decreasing globally due to measures to improve air quality and reduce emissions.

The strengthened methodology also gave new insights into the importance of the potential responses of the climate system to achieving net zero.

“Net zero” refers to achieving an overall balance between global emissions produced and emissions removed from the atmosphere.

According to the modelling results in the study, there are still large uncertainties about the years before net zero is achieved.

The climate could continue warming due to effects such as melting ice, the release of methane and changes in ocean circulation.

However, carbon sinks such as increased vegetation growth could also absorb large amounts of CO2, leading to a cooling of global temperatures before net zero is achieved.

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.”

Updated: October 31, 2023, 4:06 PM