These changes "will result in environments like we have never seen before," says Camilo Mora, a biogeographer at the University of Hawaii at Manoa and the lead author of the study, which appears in Thursday's issue of the journal Nature.
On one level, the study reaffirms a point other researchers have made in the past: that by mid-century the fingerprints of global warming will become more easy to distinguish from the ups and downs of natural climate swings.
But this study adds fresh elements to the story, researchers say.
One is a more-specific sense of timing. Dr. Mora's team delivers projections for 26 major cities. Under business as usual for emissions, the region around Manokwari, a provincial capital in eastern Indonesia, would see the shift in climate variability in 2020, give or take five years. More-aggressive emissions controls would delay that shift by about five years, the researchers estimate.
Anchorage, Alaska, on the other hand, would see the latest onset of changes as early as 2071 with business-as-usual emissions and 2095 with tougher global emissions controls.
Another is its focus on trends in climate variability across broad regions – particularly in the tropics – rather than on a single global average.
This "is desperately needed," says Frank Lowenstein, who focuses on adaptation to global warming for the Nature Conservancy, an environmental group based in Arlington, Va. Organisms in an ecosystem or culverts that civil engineers design to divert rain water are set up to endure the extremes, not the average, he explains. Changes to climate extremes can put additional stress on organisms and well as on societies.