If greenhouse emissions continue their steady escalation, temperatures across most of the Earth will rise to levels with no recorded precedent by the middle of this century, researchers said Wednesday.
Scientists from the University of Hawaii at Manoa calculated that by 2047, plus or minus five years, the average temperatures in each year will be hotter across most parts of the planet than they had been at those locations in any year between 1860 and 2005.
To put it another way, for a given geographic area, “the coldest year in the future will be warmer than the hottest year in the past,” said Dr. Camilo Mora, the lead scientist on a paper published in the journal Nature.
Unprecedented climates will arrive even sooner in the tropics, Mora’s group predicts, putting increasing stress on human societies there, on the coral reefs that supply millions of people with fish, and on the world’s greatest forests.
“Go back in your life to think about the hottest, most traumatic event you have experienced,” Mora said in an interview. “What we’re saying is that very soon, that event is going to become the norm.”
The research comes with caveats. It is based on climate models, huge computer programs that attempt to reproduce the physics of the climate system and forecast the future response to greenhouse gases. Although they are the best tools available, these models contain acknowledged problems, and it is not clear how accurate they will prove to be at peering many decades ahead.
The models show that unprecedented temperatures could be delayed by 20 to 25 years if there is a vigorous global effort to bring emissions under control. While that may not sound like many years, the scientists said the emissions cuts would buy critical time for nature and for human society to adapt, as well as for development of technologies that might help further reduce emissions.
Perhaps the most striking findings are in the tropics. Climate variability there is much smaller than in high latitudes, and the extra heat being trapped by greenhouse gases will push the temperature beyond historical bounds much sooner, the research found.
Organisms that do not have the genetic capacity to adapt to rapid climatic changes will be forced to move or will be driven to extinction, climate scientists say.