Study Finds Global Warming Fingerprint on 2022’s Northern Hemisphere Megadrought

Nobody expected the wildfire that started burning in early August on the steep, forested hillside above Stoliv, Montenegro. Residents of the village said there were no memories among the living population, nor old tales, of fire on the north-facing slope just above the Bay of Kotor that is home to ancient sweet chestnut trees and olive groves. 

The Stoliv fire burned only a few acres, but threatened homes, as well as a chestnut restoration project and the ruins of a centuries-old monastery, built in what was deemed to be the safest spot in the area.

But as the relentless, heat-fueled drought persisted across the Northern Hemisphere from June through August, it seemed to bake the very life out of the earth, threatening ecosystems as well as water, power and food supplies. In Europe, the long heat wave is estimated to have killed about 24,000 people.

Such widespread, persistent droughts are 20 times more likely in today’s climate, scientists reported today in a new World Weather Attribution study based on measurements and models of soil moisture from around the Northern Hemisphere. Co-author Friederike Otto, with the Grantham Institute, Imperial College London, said last summer shows how climate extremes aren’t just short, sharp spikes. They can affect large areas for a long time, damaging infrastructure and overburdening social systems, she said.

Hemispheric megadroughts will intensify even more as long as fossil fuel pollution keeps accumulating in the atmosphere, said co-author Maarten van Aalst, director of the Red Cross Red Crescent Climate Centre and professor of climate and disaster resilience at the University of Twente. 

“These are major impacts that are happening faster and at a larger scale than we had anticipated,” he said. But cutting greenhouse gases will, at best, prevent the extremes from worsening more. “We have to deal with what’s already there,” he said. “Adaptation is urgent. It’s no longer a choice whether we try and avoid these problems in the future by reducing emissions.”

With food security at risk in many areas, it boils down to a question of how global resources are allocated, he added.

“There is, at this point, not an absolute lack of food in the world,” he said. “So it’s to some extent a question of whether we get the food to the right people at the right time, and, in that sense, also, whether we allocate financial resources to deal with the problem, everywhere.”

The authors noted that swings between different types of extremes pose another set of problems. In 2016, water managers in France expected a hot, dry summer and kept reservoirs full. Instead, heavy rains fell, resulting in disastrous flooding. 

Otto said the new study focused specifically on agricultural and ecological drought, defined by the lack of soil moisture. Other types of studies that look at different measurements like rainfall or river flows might show different results, she said.

Co-author Sonia Seneviratne, with the ETH Zürich, said this important definition of drought was also used in a recent climate assessment by the Intergovernmental Panel on Climate Change that identified global warming impacts. 

Without human influence on the climate system, the researchers would have expected such an event in west-central Europe only once every 60 to 80 years, she said. But “under the current level of global warming, so about 1.2 degrees Celsius, it is an event that people would expect now about once every 20 years.”

Co-author Dominik Schumacher, a researcher at the Institute for Atmospheric and Climate Science at ETH Zurich, said the study shows more danger is looming ahead with more warming.  Uncertainties in the attribution study, primarily associated with a lack of direct soil moisture observations, mean that the climate models only have limited data to work with, which lowers the precision of the projections, he said. But the bottom-line findings of increased drought frequency are robust and critical for understanding impacts to agriculture and ecosystems like forests and wetlands, he added.

Impacts Hitting Harder and Sooner Than Expected

The climate change fingerprint is clear in west-central Europe, said van Aalst. 

“It’s really hitting us hard, in some of the richest parts of the world that had actually been considered less vulnerable,” he said. “I don’t think people realized that the impacts would come at us so hard, so quickly.”

Heat is the key driver in terms of direct impacts of climate on ecosystems and humans, with reports of at least 24,000 excess deaths in Europe, he said. Drought is part of a cascade of heat impacts that build on one another, he added. 

”If you look at the agricultural and ecological drought, we’re seeing the impacts compounding and cascading across regions and sectors. That’s another message that came so strongly from the IPCC earlier this year,” he said, noting that droughts also affect electricity generation and river shipping. “One case where we saw these compounding and cascading risks very clearly was in power supply, where we saw low production of hydropower, but also nuclear power struggling to dump cooling water into rivers that were already too hot,” he said.

That raised electricity prices that were already inflated due to the cut to the gas supply brought on by the war in Ukraine. At the same time,  heatwaves were driving people across Europe to consume more electricity to run their air conditioners. 

“You can see that we’re seeing ripples of that direct fingerprint of climate change with very immediate impacts,” van Aalst said. “It should be a wake up call, that we should avoid letting this problem get more out of hand, to reduce emissions.” 

“But we also need to invest more in resilience,” he said, noting that the wild swings of climate change can complicate such efforts. ”There are regions that are facing trade-offs, where in some cases, the way we prepare for extreme rainfall may be at odds with how we prepare for extreme periods of drought like this one.”

Global warming’s links to dry and wet extremes have been well-known for decades, said climate scientist Jennifer Francis with the Woodwell Climate Research Center. 

“A warmer atmosphere sucks more moisture from land and ocean, creating a vicious cycle that leads to drier soils, which in turn heat up faster and intensify heatwaves,” she said. “More intense heatwaves dry soil even further, prolonging domes of hot air in a region. And when a storm does form, that extra moisture evaporated into the air fuels heavier downpours and provides more energy for stronger storms.”

Francis, who was not involved in the attribution study, has researched how global warming is shifting critical winds like the jet stream that drive weather patterns in the Northern Hemisphere.  

“When the jet is very wavy, as it was this past June, the stage is set for both extremes,” she said. “Large jet-stream waves also tend to get stuck in place, which means the weather they create hangs around longer. Recent studies suggest these wavy patterns are occurring more frequently as the Earth continues to warm, so we should expect to see longer, more intense, more destructive droughts as well as flooding events.”

Avoiding runaway climate change requires cutting greenhouse gas emissions drastically and quickly, she said.

“If we can meet our 2030 and 2050 climate goals, and that’s a very big if, we will slow the pace of worsening extremes by mid-century,” she said. “The faster we can halt the increase in atmospheric greenhouse gases, the faster we’ll see Earth’s temperatures approach a stable level. But the longer we wait, the higher that stable temperature will be, along with the severity of extreme weather events.”