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The people who’ll be most hurt by climate swings did the least to cause them, study says

Predicted changes in temperature variability. (Sebastian Bathiany, Wageningen University)

It is no secret that not everyone on the planet is equally responsible for climate change.

On a per-capita basis, greenhouse gas emissions are far higher in wealthy countries like the United States. Indeed, the Northern Hemisphere, where 13 of the 15 largest countries by GDP are found, emits far more than the Southern Hemisphere does. But the whole globe warms as a result.

In a study released Wednesday, however, scientists have gone further in documenting what they call climate-related “inequality.” They found that tropical countries, which tend to be poorer and to have contributed less to climate change, are set to disproportionately suffer one of the more severe effects: major swings in temperature.

“There has been a lot of debate about how rich countries can help poor countries to adapt, but they have overlooked this aspect — that the impacts of climate variability change might be worse in the poorer countries,” said Sebastian Bathiany, a climate change researcher at Wageningen University in the Netherlands who led the research published in Science Advances.

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Bathiany and his colleagues from institutions in France and the United Kingdom ran a large number of climate change simulations focusing on how much monthly temperatures will tend to deviate from the average, in either direction, as global warming advances. More pronounced swings between hot and cold could mean more instances of, as we sometimes put it, weather whiplash.

The study found that in general, the tropics would see a much greater increase in temperature variability and with very serious effects, given that swings from one extreme to another can be damaging to agriculture and humans, especially if there are swings to a hot extreme.

The research found one factor in those swings involved the drying of tropical soils because of evaporation as temperature increased. As the soil dried, there was less moisture available to blunt temperature swings.

“When soils dry out, the excess energy can no longer go into evaporation but results in a stronger warming,” explained Reto Knutti, a climate researcher with ETH Zurich who was not involved in the study. “This is the same as when you get a heat stroke from dehydration: Your body cools by sweating, and when you can’t sweat any more then you overheat.”

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In the climate simulations, a particularly pronounced effect occurred in the Amazon region as it dried out. Climate variability rose by 15 percent for every 1 degree Celsius of warming. That is a development that could also be disastrous for other regions, since a warming and drying in the world’s largest tropical forest could kill off enormous numbers of trees and add far more carbon dioxide to the atmosphere, triggering more warming.

“In the natural climate, the preindustrial climate, there is a lot of evaporation in the moist tropics,” Bathiany said. “But in the future it will become drier. And because of this drying, there’s less buffering of heat. Heat waves can become stronger when there is less moisture.”

The researchers then plotted how much of an increase in temperature variability countries could expect to see in comparison with their GDP and their greenhouse gas emissions on a per-capita basis. They found that — with one big exception, Australia — countries with lower GDP tended to get hit with higher climate variability in the projections.

The study has caveats. First, when it comes to inequality, the researchers found the picture is somewhat less unfair — although still unfair — if you take into account deforestation in the tropics, which also contributes heavily to climate change. Deforestation led to more emissions from countries like Brazil and Indonesia, boosting their contributions to climate change.

Another thing to note is that although these big changes in climate variability were produced by models run to simulate a high level of warming, such changes have not been clearly observed in real-world temperature observations. But Bathiany thinks evidence is coming and probably has already arrived but that we cannot detect it yet because of a lack of data. “Especially in the tropics, we don’t have so many and so long observations,” he said.

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Knutti called the researchers’ work “straightforward and uncontroversial,” though he acknowledged the study is only as good as the models it is built on. “Getting the climate variability right in a model is much harder than getting the mean state right, and not all models are good at it,” he noted.

Another researcher, Jennifer Francis of Rutgers University, raised questions about the work.

Francis noted the method of studying variability could fail to pick up the consequences of funky behavior by the Northern Hemisphere jet stream, which Francis has argued is changing because of the fast melting of the Arctic, in turn causing extreme weather events. Her particular concern was the study looks at the deviation from temperature averages over month-long time periods, which could miss important things.

“Think of this past winter, for example: mid-February was record-breaking warm in the eastern U.S. and cool in the west; then early March brought the exact opposite conditions. This extreme variability would be smeared out by monthly averaging,” she said.

Francis agreed, however, the warming of the Arctic at a faster rate than the middle latitudes would indeed lead to less temperature variability overall when measured monthly, because there would simply be less clash between cold air masses from the north and warmer masses from the south.

So, the research does raise questions, but it nonetheless also seems to make a strong case global warming might be even more unfair to some countries than initially thought.

“There is no question that developing countries or economies in transition have historically not caused much of the climate problem, although that is changing rapidly, but suffer most from climate change,” Knutti said, “because the climate signal and its variability and changes in extremes is most prominent relative to what they were used to, because they are most vulnerable in the agricultural sector, and because they don’t have the knowledge and money to adapt.”

Knutti added, “These asymmetries are one reasons why climate negotiations are so difficult.”