U.S. will see unprecedented heat waves by midcentury

Wendy Koch | USA TODAY

Steady, unprecedented heat waves could soon hit many parts of the planet, striking the tropics first — as early as 2020 — and much of the United States by midcentury, says a study today that's based on models from 21 climate centers worldwide.

So in 2043, for example, Phoenix and Honolulu could see their average air temperatures shift beyond the most extreme records of the past 150 years if greenhouse gas emissions continue at their current pace, says the study published in the peer-reviewed journal Nature. That could occur in 2047 for New York City, Philadelphia and Washington, D.C., and in 2048, for Los Angeles and Denver. In other words, whatever the record warmest year was for those cities before then, every year after that point will likely be warmer.

"What's shocking is how soon this is going to happen," says lead author Camilo Mora,a data analyst and geography professor at the University of Hawaii, Manoa. "This is something we're doing to ourselves," not just to future generations, he says, adding that within 35 years, "whatever climate we were used to will be a thing of the past."

His team developed an index, based on data from 39 climate models used in 12 countries, for when the climate of any spot on Earth will continuously exceed the extremes recorded between 1860 and 2005. They found that the planet's oceans began surpassing historical extremes for acidity in 2008, because they've absorbed significant amounts of human-caused carbon dioxide emissions.

The study says the world's climate is already changing, but the index -- a sort of tipping point -- shows when a "radically different climate" could begin for any particular location. It says the onset could be delayed if heat-trapping emissions are curbed.

"This paper is unusually important," Jane Lubchenco, former head of the National Oceanic and Atmospheric Administration and now professor at Oregon State University, said in a statement. She said the study, which she did not work on, "connects the dots between climate models and impacts to biodiversity in a stunningly fresh way."

Stuart Pimm, a professor at Duke University's Nicolas School of the Environment, agrees. He says the findings may seem counter-intuitive, because the Arctic is warming more than the tropics. Yet he says the Arctic is used to rapid change but the tropics are not, so the latter is departing from historical norms sooner.

"That's going to cause societal disruptions," Pimm says, noting there's more ecological biodiversity as well as human poverty in the tropics than in the Arctic.

The study projects Indonesia could see a huge shift beginning in 2020, and Malaysia's Kuala Lumpur as well as Nigeria's Lagos in 2029. It says extreme climates, especially in the tropics where more than a billion people live in predominantly developing countries, raise concern about food shortages, wider spread of infectious disease and species' extinction.

"We will push marine ecosystems out of their historical "habitable zones,"" if current trends in greenhouse gas emissions continue, says Ken Caldeira, a climate scientist at the Carnegie Institution for Science, who was not involved in the study. He says some species may be able to adapt but others, such as coral reefs, likely won't.

Caldeira says that while there are "uncertainties" in the details of climate models, the study's findings are "robust" and suggest the need to reduce greenhouse-gas pollution..

Mora said the university funded all the research except for a $5,000 NOAA grant for an advanced computer to do the data analysis. He says his team has no policy agenda but agrees emissions need to be curbed. Temperatures that were once the maximum will soon become the new minimum, he says, adding: "We're not ready for it.'