Tropics will be the first region to be hit hard by global warming

Scientists have determined when the climates of numerous locations around the world will shift to a new, hotter normal as a result of higher greenhouse gas emissions, according to a study released Wednesday in the journal Nature.

The tropics appear most likely to be the first to shift to an unprecedented new climate, perhaps as early as the next decade, the analysis shows. The average location on Earth could experience a substantially different climate by 2047 if human beings continue to do little to rein in emissions of heat-trapping gases, the report warns.

The shifts to consistently warmer temperatures in the world’s climates pose a considerable threat to thousands of plant and animal species. They would either have to move, adapt or face extinction.

Most aspects of human society would face grave disruptions as well, from agriculture to water security to public health.

“Regardless of the scenario, changes will be coming soon,” said Camilo Mora, an assistant professor of geography at the University of Hawaii, Manoa, and the study’s lead author. “Within my generation, whatever climate we were used to will be a thing of the past.”

Even if nations took a more aggressive approach to reducing greenhouse gases, the annual mean temperature in an average location in the world would still shift out of its previous normal range by 2069, Mora and his colleagues found.

The inevitability of the global shift to hotter climates should not be seen as a cause for inaction, warned the study’s authors and others who read the paper. Rather, it highlights the urgency of adopting measures that would give people and other organisms better odds of coping with their new, hotter environs, they said.

“The optimistic way to look at this is that taking steps to reduce emissions is buying us time — for species to adapt, for human societies to change and to come up with technological advancements,” said study coauthor Abby Frazier, a graduate student in geography at the University of Hawaii, Manoa. “It lets us put on the brakes. If you were about to get into an accident, wouldn’t you want it to happen at 20 miles per hour rather than 80?”

Mora said the research arose from the realization that while there were many studies looking at the absolute change in global temperature and the speed of the transformation, there was a gap in knowledge regarding the timing of such shifts.

The team’s findings are based on annual average temperatures around the world over the last 150 years. The notion of a shift to a different climate means that the annual average temperature for a given location will be consistently outside the bounds of its current range.

“We set the bounds of the past minimum and maximum values, and the shift is when the annual mean temperature moves beyond these bounds and never comes back in,” said study coauthor Ryan Longman, also a graduate student in geography at the University of Hawaii, Manoa. “The new minimum temperature of the future is the old maximum temperature of the past.”

Many studies have focused on the great temperature increases expected in the Arctic. But the new study’s conclusion that the tropics will suffer unprecedented temperature changes first surprised experts who weren’t involved in the research.

The swift changes expected for the tropics “immediately raises all sorts of alarms bells,” said Stuart L. Pimm, an expert on the tropics and professor of conservation ecology at Duke University. “The greatest variety of life and biodiversity and the poorest people in world live in tropics, and the new climate shifts will be outside their parents’ and grandparents’ experience.”

Pimm added: “The past is no longer prologue.”

As climate change has begun to make traditional habitats less hospitable for various species, they have moved to cooler places or higher altitudes. But in the tropics, there are far fewer opportunities for plants and animals to do that, Pimm said.

“They can’t so easily disperse to get to that comfort level again,” Pimm said. “So given that, there’s a very, very severe worry about this will do to species in the tropics.”

neela.banerjee@latimes.com

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