Billions of people could be living in regions where temperatures are hotter than their historical ranges by mid-century, creating a new normal that would impose profound changes on nature and society, scientists said on Wednesday.
Temperatures in an typical location in an average year would be hotter by 2047, than those in the warmest year from 1860-2005 if greenhouse gas emissions continue to rise, with the tropics the first affected area, a new index indicated. Eventually, the coldest year in a particular city or region will be hotter than the hottest year in its past.
"The results shocked us. Regardless of the scenario, changes will be coming soon," lead author Camilo Mora of the University of Hawaii said. "Within my generation whatever climate we were used to will be a thing of the past."
The data, published in the journal Nature, suggested the cities to be hit earliest included Manokwari in Indonesia, which could shift to a new climate from 2020. The earliest U.S. cities to hit that threshold would be Honolulu in 2043 and Orlando in 2046.
At the other extreme, Moscow and Dallas would depart from historical variability in 2063 and Anchorage not until 2071.
In all, the scientists found that between 1 and 5 billion people would be living in regions outside such limits of historical variability, underscoring the impact already under way from a build-up of man-made greenhouse gases.
"Unprecedented climates will occur earliest in the tropics and among low-income countries," according to the study, which urged cuts in greenhouse gases to limit damage to human society and wildlife.
Ken Caldeira of the Carnegie Institution for Science’s Department of Global Ecology said the study “demonstrates that we are pushing the ecosystems of the world out of their environment in which they evolved into wholly new conditions that they may not be able to cope with.”
“Extinctions are likely to result,” he added, specifically mentioning Earth’s rapidly dwindling coral reefs.
Commentators noted, however, that the study did not fully address how people may become better adapted at dealing with the warming, potentially buffering against some of its effects.