A federal scientific panel said Tuesday that climate change has “moved firmly into the present.”
The resulting shift in long-term weather patterns carries some beneficial effects — crops grown where they were impractical before — but the group’s report said “many more are detrimental.”
In the American Southeast and Caribbean region, for example, the report said rising sea levels, extreme heat events, hurricanes and decreased water resources have grown more common.
In the Midwest, droughts and heat waves last longer and bake hotter. But when rains come, they fall with more force and a greater likelihood to unleash flash floods.
The findings from the U.S. National Climate Assessment grew from a three-year project involving more than 300 experts and top administration officials. The report was called for in President Barack Obama’s climate action plan, launched last year.
Such gloomy assessments confirm what many climate scientists have warned about for years: It’s not just that average temperatures are climbing, they say, but that such a shift in climate invites more extremes.
“We’re not talking about what’s going to happen in the future now,” said Jimmy Adegoke, the director of the Laboratory for Climate Analysis and Modeling at the University of Missouri-Kansas City. “We’re talking about what’s already happening.”
In the Midwest, the report says, longer growing seasons and rising carbon dioxide levels will increase the yields of some crops, though those benefits will be offset by extreme weather.
In the Great Plains, rising temperatures trigger increased demands for water and energy. That might constrain development and increase competition for water among cities, agriculture and energy production.
“What had been a normal-precipitation drought now becomes a deep-grade drought,” said Tom Brikowski, a geosciences professor at the University of Texas-Dallas and a scholar of Great Plains climate. “And normal in the region becomes a low-grade drought.”
In the Southwest, snow-pack and stream-flow amounts are projected to decline, decreasing the reliability of surface water supplies and threatening the region’s production of specialty crops. Warming, drought and insect outbreaks tied to climate change have increased wildfires as well as affected people and ecosystems.
In the Northwest, changes in snow melt have been observed and will continue, reducing water supplies. The combined impact of increasing wildfires, insect outbreaks and plant diseases has already caused widespread tree deaths and is “virtually certain to cause long-term transformation of forest landscapes.”
Seven major ports in the Southeast are vulnerable to sea level rise, the report said. Residents can expect a significant increase in the number of hot days — defined as 95 degrees or above — and decreases in freezing events.
“Large numbers of southeastern cities, roads, railways, ports, airports, oil and gas facilities and water supplies are vulnerable to the impacts of sea level rise,” the report concludes.
A draft of the report had been released previously, and the report’s authors received more than 4,000 public comments.
Skeptics of climate change attacked the report. The Cato Institute, a Washington-based libertarian research center, said Monday that the report “overly focuses on the supposed negative impacts from climate change while largely dismissing or ignoring the positives from climate change.”
It said the “bias towards pessimism” has implications for the federal regulatory process because the report is cited as a primary source for the science of climate change in justifying federal regulations.
Because the U.S. National Climate Assessment “gets it wrong, so does everyone else,” Cato’s authors said.
The report lays out climate change scenarios that have affected or may affect different regions and sectors of the economy.
White House officials on Tuesday said the report’s state-by-state, region-by-region impacts might help move the climate change debate forward. White House adviser John Podesta called it “actionable science.”
“For decades we’ve been collecting the dots on climate change,” added Jerry Melillo, a scientist at the Marine Biological Laboratory who led the committee that oversaw the report. “Now we are connecting those dots.”
Researchers in the Midwest have been monitoring climate changes for decades. At the Konza Prairie Long Term Ecological Research Network site in the Flint Hills, scientists have detected individual grass species evolving with changing weather patterns.
It’s not just how much rainfall the prairie gets that matters, said Kansas State University biology professor John Blair, it’s when that rain comes. Less rain in early summer, even if more comes later, means less grassland production.
“We grow less grass,” said Blair, the director of the Konza project. That could have implications for ranchers grazing cattle in the region.
As much as rising temperatures, said University of Kansas geography professor Johan Feddema, the changes mean more wild swings in weather. He compared shifting patterns to a stream hitting a plateau, causing meandering swirls. More cold air drifts south, more hot air blows north.
“One outcome of climate change,” he said, “is greater variability.”
Not all climate changes are bad, the report concludes. Some, such as a longer growing season in some regions and a longer shipping season on the Great Lakes, “can be beneficial over the short run.”
“But many more are detrimental, largely because our society and its infrastructure were designed for the climate that we have had, not the rapidly changing climate we now have and can expect in the future,” the report says.