Climate crisis: Researchers call for a better definition of the 1.5 degree limit

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Climate crisis: Researchers call for a better definition of the 1.5 degree limit

"The 1.5 degree limit has been exceeded" - according to the currently applicable criteria, experts could only make such a statement about the climate crisis many years later. British researchers recently warned about this in a commentary in the journal Nature. They make a suggestion as to how non-compliance with climate targets could be certified much earlier.

At the 2015 World Climate Conference in Paris, countries around the world agreed to limit global warming to 1.5 degrees compared to pre-industrial times. The current world climate conference in Dubai is also about maintaining this mark. The 1.5 degree target refers to longer-term values ​​and not to individual days, months or years. But when exactly can we say: the goal was missed?

"It may be surprising that the Paris Declaration does not contain a formally agreed definition of the current state of global warming," Richard Betts and his colleagues from the Met Office and the University of Exeter explain in their commentary.

"Without agreement on what actually counts as exceeding 1.5 degrees Celsius, we risk distraction and confusion at the very time when action to avert the worst effects of climate change becomes even more urgent," Betts said. Many experts now assume that the 1.5 degree target can no longer be achieved.

Years of delay

The Intergovernmental Panel on Climate Change (IPCC) has defined when a certain temperature mark is considered to be exceeded. To do this, the experts look at the global average temperature averaged over a period of 20 years. For example, if the mean is 1.5 degrees above the pre-industrial average, the experts set the middle of the 20-year period as the moment at which this threshold was exceeded for the first time. “This means that we can only determine that a threshold has been exceeded 10 years after that date,” said Chris Hewitt, director of climate services at the World Weather Organization (WMO), when asked.

The problem becomes clear using the example of the 1 degree threshold: The period from 2002 to 2021 was the first in which the average global temperature was one degree above pre-industrial times. It was determined - and only at the end of this long period - that the 1 degree threshold was exceeded around 2012.

The WMO is considering commissioning an international team of experts to examine alternative methods to enable a more timely assessment, Hewitt said.

Suggestion from experts

Betts' group proposes calculating the level of global warming from observation data from the past ten years as well as model projections for the next ten years. This further ensures that the average value over a period of 20 years is taken into account. However, if the 1.5 degree threshold is exceeded, it could be detected in good time and measures could be tightened, according to the scientists. Using the proposed method, the researchers calculated that global warming at the end of 2022 was around 1.26 degrees compared to pre-industrial levels.

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