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The seesaw variability of global temperatures often engenders debate over how seriously we should take climate change. But within 35 years, even the lowest monthly dips in temperatures will be hotter than we’ve experienced in the past 150 years, according to a new and massive analysis of all climate models. The tropics will be the first to exceed the limits of historical extremes and experience an unabated heat wave that threatens biodiversity and heavily populated countries with the fewest resources to adapt.

Ecological and societal disruptions by modern climate change are critically determined by the time frame over which climates shift. Camilo Mora and colleagues in University of Hawaiʻi at Mānoa College of Social Sciences’ Department of Geography have developed one such time frame. The study, entitled “The projected timing of climate departure from recent variability,” was published in the October 10 issue of Nature and provides an index of the year when the mean climate of any given location on Earth will shift continuously outside the most extreme records experienced in the past 150 years.

The new index shows a surprising result. Areas in the tropics are projected to experience unprecedented climates first within the next decade. Under a business-as-usual scenario, the index shows the average location on Earth will experience a radically different climate by 2047. Under an alternate scenario with greenhouse gas emissions stabilization, the global mean climate departure will be 2069.

“The results shocked us. Regardless of the scenario, changes will be coming soon,” said lead author Mora. “Within my generation, whatever climate we were used to will be a thing of the past.”

The scientists calculated the index for additional variables including evaporation, precipitation and ocean surface temperature and pH. When looking at sea surface pH, the index indicates that we surpassed the limits of historical extremes in 2008. This is consistent with other recent studies, and is explained by the fact that ocean pH has a narrow range of historical variability and because the ocean has absorbed a considerable fraction of human-caused CO2 emissions.

The study found that the overarching global effect of climate change on biodiversity will occur not only as a result of the largest absolute changes at the poles, but also, perhaps more urgently, from small but rapid changes in the tropics.

Tropical species are unaccustomed to climate variability and are therefore more vulnerable to relatively small changes. The tropics hold the world’s greatest diversity of marine and terrestrial species and will experience unprecedented climates some 10 years earlier than anywhere else on Earth.

In predominately developing countries, over one billion people under an optimistic scenario, and five billion under a business-as-usual-scenario, live in areas that will experience extreme climates before 2050. This raises concerns for changes in the supply of food and water, human health, wider spread of infectious diseases, heat stress, conflicts and challenges to economies. “Our results suggest that countries first impacted by unprecedented climates are the ones with the least capacity to respond,” said coauthor Ryan Longman. “Ironically, these are the countries that are least responsible for climate change in the first place.”

While the study describes global averages, the authors have visualized their data on an interactive map displaying when climate will exceed historical precedents for locations around the world. “We hope that with this map people can see and understand the progression of climate change in time where they live, hopefully connecting people more closely to the issue and increasing awareness about the urgency to act,” said coauthor Abby Frazier.

The study suggests that any progress to slow ongoing climate change will require a larger commitment from developed countries to reduce emissions, but also more extensive funding of social and conservation programs in developing countries to minimize climate change impacts. The longer the wait, the more difficult remediation will be.

“Scientists have repeatedly warned about climate change and its likely effects on biodiversity and people,” said Mora. “Our study shows that such changes are already upon us. These results should not be reason to give up. Rather, they should encourage us to reduce emissions and slow the rate of climate change. This can buy time for species, ecosystems, and ourselves to adapt to the coming changes.”

For more, download the full news release.