Way back from climate overshoot is clear, feasible and necessary

The path to ending climate overshoot and returning global warming below 1.5°C by 2100 is clear, feasible and necessary, concludes a new flagship report from global climate science and policy institute Climate Analytics, published as world leaders arrive in Antalya, Türkiye for the high-level segment of COP31.

Climate Overshoot: The way back below 1.5°C shows that by the highest possible ambition deploying a set of critical levers centred on a rapid phase-out of fossil fuels and deep methane reductions, governments can halt global warming by mid-century, limit peak warming to 1.7°C, and return below 1.5°C, and ideally well below 1.5°C by 2100 [2].

It also shows that while overshoot will bring impacts and risks that could have been avoided had governments kept warming below 1.5°C, minimising the scale and duration of overshoot and bringing warming back below 1.5°C by 2100 will constrain the further rise in impacts and risks.

“Governments' past policy failures have made overshoot unavoidable, and their populations and economies are feeling the impacts of that,” said Bill Hare, CEO of Climate Analytics and the report’s lead author.

“But it doesn’t have to continue like this: how high temperatures go and how long we spend at profoundly unsafe levels of global warming is a political choice.

“In this report we’re showing world leaders coming to COP31 what’s needed to make the right choice for their people and economies, and what’s at stake if they don’t.”

The Paris Agreement of 2015 adopted 1.5°C as the limit for global warming, and last year the International Court of Justice reaffirmed that governments have a duty under international law to pursue it – a judgement endorsed by the United Nations General Assembly in July.

Impacts and risks

Every additional 0.1°C increases climate impacts such as heat exposure, heat extremes, sea level and tipping point risks.

At 1.7°C, about one-third more people will be exposed to heatwaves in a range of countries than at 1.5°C: at 1.8°C, the number rises by a further 10% or more. The benefits of fast emission cuts could accrue rapidly, as recent research indicates that the frequency of extreme heat events is related to the speed of temperature rise.

Returning to 1.5°C after overshoot would not be enough, as recent research shows that stabilizing at this level of warming could trigger important tipping points, including:

• widespread coral reef dieback, with 96% of shallow-water reefs already assessed as Critically Endangered
• irreversible melting of the Greenland and West Antarctic ice sheets, which together would trigger lobal sea-level rise of 13 metres over centuries
• die-back of the Amazon rainforest (caused by a combination of climate change and deforestation).

Restraining impacts and risks would in turn reduce the need for adaptation and international financing for it. It would also keep adaptation open as an option for more societies and ecosystems, and constrain the global cost of Loss and Damage.

This would be particularly beneficial to small island developing states (SIDS) and Least Developed Countries (LDCs). SIDS already lose an estimated 1-9% of annual GDP to climate impacts, while more than two-thirds of deaths caused by climate-related disasters occur in LDCs, along with a disproportionate share of economic damage.

However, the report also shows how big emitters gain from embarking on a path to minimise overshoot and return below 1.5°C by 2100.  In both China and the US, it would almost halve the number of people exposed to heatwaves, compared with a 2°C trajectory. It would benefit crop yields in China, the EU and India, and reduce coastal flood risk worldwide.

The way back

The report shows it is eminently possible to embark now on a pathway that keeps peak warming to 1.7°C around mid-century, reaches net zero greenhouse gas emissions by the 2070s and returns global warming to 1.2-1.3°C by 2100.

The centrepiece is phasing out fossil fuels, beginning by halving their use by 2035. Renewables would replace fossil fuels in electricity generation, and clean electricity would replace them in transport, buildings and industry. Zero-carbon fuels such as green hydrogen would replace fossils in a few niche uses. Energy efficiency gains would reduce the total amount of energy needed.

These central measures would be supplemented by rapid cuts in methane emissions from energy, waste and agriculture, restoration of natural ecosystems and an end to deforestation, and a scale-up of carbon dioxide removal (CDR) to take CO2 out of the air.

“We have virtually all of the tools we need to do this,” said Dr Marcia Rocha, 1.5°C Overshoot Hub lead at Climate Analytics and the report’s coordinator.

“And in many cases the clean option is also the cheap and secure option, because moving away from fossil fuels in a world of volatile geopolitics is just a pragmatic thing to do.

“The report shows that we are indeed in a deep hole, created by governments’ collectively apathetic response to the climate crisis: but it also very clearly indicates that there is a way out, and that world leaders gathering here at COP31, led by its twin chairs Türkiye and Australia, need to start taking the first steps back towards a cooler, fairer and safer world.”

Climate Overshoot: The way back below 1.5°C is the first edition of a new annual flagship assessment by Climate Analytics of the impacts of overshoot and what is needed to minimise it and return below, or better well below 1.5°C, by 2100.

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