'Unprecedented' weather changes: 70 per cent of the world could be affected
"The only way to deal with this is to prepare for a situation with a much higher likelihood of unprecedented extreme events, already in the next one to two decades," says researcher Bjørn Samset.
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Norwegian researchers have calculated that 70 per cent of the world's population will experience a strong increase in peak temperatures or intense rainfall over the next 20 years, if greenhouse gas emissions increase significantly.
Such a drastic change in temperature and rain almost never happened in a climate without human-made climate change, according to the new study conducted by CICERO, the Center for International Climate Research.
The changes in the next 20 years will be far beyond what has been normal and will be ‘unprecedented,’ according to the study.
At best, 1.5 billion people will be affected
Tropical and subtropical areas are expected to experience the most significant changes.
If the world manages to achieve the two-degree target from the Paris Agreement, the proportion experiencing ‘unprecedented changes’ will drop to 20 per cent of the world's population. However, this still includes countries like India and those on the Arabian Peninsula.
"In the best-case scenario, these rapid changes will affect 1.5 billion people by 2040. In the worst case, we're talking about around 5.5 billion people," climate researcher Bjørn H. Samset says in an article from CICERO (link in Norwegian).
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“The only way to deal with this is to prepare for a situation with a much higher likelihood of unprecedented extreme events, already in the next one to two decades,” he says.
Even if we follow the two-degree scenario, we still need to be prepared for rapid changes and adapt to them, says CICERO researcher Carley Iles, who led the study.
How rapidly will things change?
In the study, researchers relied on numerous simulations using climate models.
They did not run the climate models themselves but downloaded the results.
The researchers focused on the five consecutive days of the year with the most rainfall and the day of the year with the highest temperature.
They examined how much the maximum temperature has increased per decade and whether it has rained more or less on the days with the most rainfall.
They compared the years 2021 to 2040 with pre-industrial times, from 1850 to 1900.
The researchers looked at whether future changes will surpass the natural variations of the past.
“Even in a climate without human-made climate change, there would have been some variation,” says Iles.
However, researchers observed that in many regions, the temperature on the hottest days is projected to rise by about 0.5 degrees per decade. Previously, the most common change was close to 0 degrees.
For maximum rainfall over five days, the pattern varied more across different regions. Yet in most areas, the amount of rainfall increased more per decade than what was previously normal.
Unusually rapid changes in extreme weather
The researchers have found that most of the world, including Norway, will experience a rate of change in extreme weather that they describe as ‘unusual.’
This applies to both the worst and best future scenarios.
This means that such changes over two decades could have occasionally occurred in pre-industrial times, but they would have been rare.
But is it really that dangerous if the hottest day of the year gets a little warmer? It's just one day, after all.
“While we focus on the hottest day of the year in our study, other research has shown that heatwaves, in general, are becoming warmer and more frequent. We expect that annual and seasonal average temperatures will also rise,” says Iles.
“So I expect we would find the same results if we used a broader definition of heatwaves, encompassing several consecutive days,” she adds.
Particularly rapid changes in warmer regions
The researchers also looked at maximum temperature and rainfall separately.
“Almost the entire world will experience unusually rapid changes in temperature extremes, but in some regions, the changes will be especially fast,” Iles says.
“In terms of temperature, parts of Africa, the Mediterranean, the Arabian Peninsula and parts of South America will experience the greatest changes,” she says.
As for rainfall, there was only one area where the change exceeded the threshold to be called ‘unprecedented,’ and that was in central Africa under the worst climate scenario.
"In regions with 'unusually rapid change,' high-latitude areas, East and South Asia, and central Africa stood out," she says.
Norway will also experience unusual changes in rainfall in the worst-case scenario.
Due to the way the calculations were done, it was easier to exceed the two thresholds for combined rainfall and temperature than for each individually, Iles explains.
Interesting study, but rough description
The increase in global warming raises the likelihood of more frequent and intense rainfall events, partly because warmer air can hold more moisture, according to the Norwegian Meteorological Institute (link in Norwegian).
Research from the institute also suggests that climate change will cause rainfall to cluster over smaller areas, making it more intense.
Rasmus Benestad, a climate researcher at the Meteorological Institute, finds the study interesting.
He points out that global climate models have limitations when it comes to extreme weather because they are designed to recreate broad patterns, not local conditions like extreme rainfall in small areas.
Because of this, international research groups have developed a program called the Coordinated Regional Climate Downscaling Experiment (CORDEX).
In this program, results from global climate models are processed by adding information about local conditions and how they interact with larger-scale changes. This process is known as downscaling.
“The global climate models only offer a rough description of, for example, mountains and landscapes, resulting in an image with coarse pixels. They don’t provide good enough detail to assess the consequences of changes for the environment and society,” says Benestad.
He also emphasises the importance of evaluating the models being used, to ensure they can accurately reproduce the conditions necessary for studying historical trends in maximum annual temperature and extremely wet five-day events.
“There are many studies that don’t place much emphasis on evaluation, but this study does to some extent. I would say the results paint a credible picture, but should still be taken with a grain of salt – something that is also acknowledged in the article,” he says.
Flatten out
The researchers behind the new study also looked at what happens after 2040.
In the low-emissions scenario, the increase in maximum temperature and rainfall intensity begins to level off and stabilise by 2100. Temperature and rainfall will then remain at a higher level than before.
The extremes, on the other hand, continue to rise in the high-emissions scenario.
The researchers point out that climate change will affect a large part of the world's population, even with significant emission reductions.
Reference:
Iles et al. Strong regional trends in extreme weather over the next two decades under high- and low-emissions pathways, Nature Geoscience, vol. 17, 2024. DOI: 10.1038/s41561-024-01511-4
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Translated by Nancy Bazilchuk
Read the Norwegian version of this article on forskning.no
