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Study Projects Arrival of ‘Unprecedented Climates’

Forest on Barro Colorado
Some parts of the world will see their climate conditions move continuously beyond the bounds of the norm as soon as 2047, according to a new analysis. Tropical regions will be hardest hit. Wikimedia Commons/Christian Ziegler

New research into climate models reveals that mean temperatures will fall outside of recent historical bounds by midcentury.

October 22, 2013—Working with a suite of 39 global climate models, a professor and a team of students at the University of Hawaii, Manoa, have developed new projections of when the mean climate in specific locations around the world will change to the extent that the climate can be considered continually beyond the bounds of recent historical norms.

The team, led by Camilo Mora, Ph.D., an associate professor in the Department of Geography, used the 145-year period between 1860 and 2005 as a basis of the research. They examined two scenarios involving carbon dioxide emissions, one involving significant reductions in emissions and one involving a “business as usual” scenario in which high population growth and a strong economy fuel continuing emissions at high levels.

The resulting research report, “The Projected Timing of Climate Departure from Recent Variability,” was published in early October in the journal Nature. The team found that under the high-emissions scenario, the global mean moves outside of historical boundaries in 2047. Under the reduced emissions scenario, the date is not much later: 2069.

Under the reduced-emissions scenario, 1 billion people will be affected by climate conditions that are outside of recent historical parameters by 2050. Under the high-emissions scenario, that number jumps to 5 billion. If the climate significantly alters an area’s ability to support agriculture, the impacts will be pronounced, says Mora, who specializes in biodiversity. “When I saw the results, I was very surprised,” Mora says. “I was thinking there is no way future variability is going to exceed those boundaries.”

Mora says that the historical base period was selected to provide a conservative basis for the research. The long time frame and inclusion of decades of the later industrial period created a broader range than an earlier or more narrow period might have. “We were very conservative on the approach we were taking at that point,” Mora says. “So when we saw the future temperatures exceeding these bounds by 2047, it was quite surprising. I was thinking it was going to be a lot later.

“The other surprising thing was that we analyzed a scenario in which we take a very aggressive mitigation of greenhouse gasses. It was my expectation that that scenario was going to keep the climate within historical bounds,” he says. “So [it] was surprising to me when we found that even under that scenario, the climate will still exceed historical records.”

The team processed more than 1 million maps, each with 60,000 data points. The 39 global climate models were used to provide as broad a spectrum as possible and to gauge the level of disagreement they would produce.

“It was our interest to analyze every single model that is out there. No matter how good or how bad they are, we wanted to have them all—just to see how consistent the responses were,” Mora says. “To my surprise, they were very consistent. We are talking about models that have been developed by people who don’t speak the same language; countries that have very different political agendas; mathematical formulations that are completely different. Yet all of those models are giving the same response. The margin of error that we found was only plus or minus five years.”

The team found that varying the time frame of the historical reference period—by say, using a 20-year period or a 1,000-year period—changed the projected out-of-bounds date by only about two years. They did find, however, that when they varied the definition of a sustained departure from the historical range to a smaller range of consecutive years, there was a more significant effect. When departure is determined by fewer consecutive years outside of the historical bounds, the date of the change is much sooner. The research indicates that the areas that will experience unprecedented climate conditions soonest will be those in the tropics. Because tropical regions are home to a large portion of the world’s biodiversity, and because many tropical species have a limited tolerance to climate changes, this could be especially problematic, Mora says.

“We have very good evidence from records in our very recent past in which the climate had reached extreme events and species responded quite dramatically to these changes,” Mora says. “There are three ways in which a species can deal with this. One is for them to move to other places. Some species might not have capacity to move, so they will stay and they will try to adapt. The last thing that [we] want [them] to do is go extinct, but that’s the third option.”



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