Climate graphic of the week: Record ice sheet melt in September as emissions rise

Record ice sheet melting in Greenland was identified in September, among the planetary tipping points that scientists warned would be triggered by climate change, even as new data showed global greenhouse gas emissions continue to rise.

Global carbon emissions surged in 2021 after a temporary easing during the pandemic, and preliminary data found they were 1.2 per cent higher again in the first five months of 2022 compared with the same period in 2019, based on the latest research from the Global Carbon Project published last week.

At the same time, Nasa’s Earth Observatory said “vast areas” of Greenland’s ice sheet had melted in recent weeks, “the most on record for any September”.

That came as a study published in the journal Science found that five major tipping points — self-reinforcing and irreversible negative changes, such as the melting of major ice sheets — could be crossed at the level of global warming already reached.

“Several of them have become possible . . . 1C [of warming] is where things started to become destabilised and unsafe,” said lead author David Armstrong McKay, speaking to the Financial Times after a three-day tipping points conference that drew together some of the foremost scientists in the field.

Six other tipping points, including the collapse of the Greenland and West Antarctic ice sheets and the die-off of low-latitude coral reefs, would become “likely” even if the world were to meet the Paris Agreement goal of limiting warming to between 1.5C and 2C. The world has already warmed by at least 1.1C due to human activity.

“Observations have revealed that parts of the West Antarctic ice sheet may already have passed a tipping point,” the paper warned. “Potential early warning signals of Greenland ice sheet . . . have been detected.”

The science of tipping points has evolved over the past 15 years since the first major study of them in 2008 by Tim Lenton, now at the University of Exeter where the experts gathered this week.

Recent findings have revised down the estimated level of warming that would be required to cross some tipping points, while in some cases crossing one could make others more likely to be crossed, said Armstrong McKay.

The findings “provide really strong scientific support of the Paris Agreement aim of [limiting warming to] 1.5C”, he added.

Last year, the world’s top climate scientists agreed that the probability of “low-likelihood, high-impact outcomes” such as crossing tipping points would increase with every fraction of a degree of warming, in one of the UN Intergovernmental Panel on Climate Change reports.

Concluding with certainty that the runaway collapse of ice sheets had started was likely to be more difficult than establishing that tropical coral reefs were in the process of dying, for example, since the former could take thousands of years while the latter could only take a decade.

Countries are being encouraged to upgrade their emissions reduction plans ahead of November’s COP27 climate summit. Pledges made as of November 2021 were “insufficient” to limit warming to 1.5C above pre-industrial levels, the UN Environment Programme has concluded.

The UK’s Met Office, working with the World Climate Research Programme, has also estimated that there is a 48 per cent chance that the annual mean global temperature will temporarily reach 1.5C during at least one year in the next five.

Lenton, speaking to the FT alongside Armstrong McKay, said humanity’s “best and possibly last hope” of limiting warming to 1.5C was to “find and trigger some positive tipping points” that would accelerate decarbonisation.

Examples of such virtuous circles included the growing adoption and falling price of electric vehicles and solar energy.

Otherwise, with negative tipping points looming, he said, “we really have to start thinking about how do we adapt to what might become the inevitable.”

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