POTSDAM, Germany — Scientists in recent observation data find a 90-fold increase in the frequency of monthly heat extremes in the past 10 years compared to 1951-1980.
Their analysis provided by Potsdam Institute for Climate Impact Research reveals that so-called 3-sigma heat events, which deviate strongly from what is normal in a given region, now, on average, affect about nine percent of all land area at any time.
Record daily rainfall events also increased in a non-linear way — on average, one in four rainfall records in the last decade can be attributed to climate change.
Already at present, extreme events linked to human-caused climate change are at unprecedented levels, the scientists say, and they must be expected to increase further.
“For extreme extremes, what we call four-sigma-events that have been virtually absent before, we even see a roughly 1000-fold increase compared to the reference period,” said lead-author Alexander Robinson from the Complutense University of Madrid Spain, and Potsdam Institute for Climate Impact Research, Germany.
“They affected about three percent of global land area in 2011-20 in any month.”
“This confirms previous findings, yet with ever-increasing numbers. We are seeing extremes now which are virtually impossible without the influence of global warming caused by greenhouse gas emissions from burning fossil fuels,” Robinson said.
The term ‘sigma’ refers to what scientists call a standard deviation.
For example, 2020 brought prolonged heat waves to both Siberia and Australia, contributing to the emergence of devastating wildfires in both regions.
Both events led to the declaration of a local state of emergency. Temperatures at life-threatening levels have hit parts of the US and Canada in 2021, reaching almost 50°Celsius.
Globally, the record-breaking heat extremes increased most in tropical regions since these usually have a low variability of monthly temperatures. However, as temperatures continue to rise, record-breaking heat will also become much more common in mid-and high-latitude regions.
Daily rainfall records have also increased. Compared to what would have to be expected in a climate without global warming, the number of wet records increased by about 30 percent.
This implies that one in four records is attributable to human-caused climate change. The physics background is the Clausius-Clapeyron relation, which states that air can hold seven percent more moisture per degree Celsius of warming.
Importantly, already dry regions such as western North America and South Africa have seen a reduction in rainfall records. In contrast, wet regions such as central and northern Europe have seen a substantial increase.
Generally, increasing rainfall extremes do not help to alleviate drought problems.
Comparing the new data with the previous decade of 2000-2010, the data show that the land area affected by heat extremes of the three-sigma category roughly doubled.
Those deviations that are so strong have previously been absent, the four-sigma events newly emerged in the observations.
Rainfall records have increased a further five percentage points in the last decade. The seemingly small amount of warming in the past 10 years, just 0.25°Celsius, has thus pushed up climate extremes substantially.
“These data show that extremes are now far outside the historical experience. Extreme heat and extreme rainfall are increasing disproportionally,” said co-author Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research.
The scientists also affirmed that their analysis confirms that every tenth of a degree matters for the impacts of global heating on humans.
(With inputs from ANI)
Edited by Ojaswin Kathuria and Pallavi Mehra