WASHINGTON — The federal government’s sweeping new National Climate Assessment is more than just a dire warning about current and future global warming effects across the United States. It’s also the most detailed guide yet to all the ways the country will have to adapt.
Even if the nations of the world get their act together and slash fossil-fuel emissions rapidly, the United States will need to spend many billions of dollars to harden coastlines, rebuild sewer systems and overhaul farming practices to protect against floods, wildfires and heat waves that are already causing havoc nationwide. And the more that emissions rise, the more difficult and costly that task gets.
The United States isn’t prepared. In the Midwest, the report notes, only four counties and cities have written climate change plans. This in a region where scientists are forecasting bigger crop failures and heavier floods that could cripple transportation networks. And at the federal level, the Trump administration is rolling back policies to take future sea-level rise into account when building new roads and railways.
Below are five major steps the scientific report says the country will need to take in the decades ahead:
1. Rethink how we farm
The nation’s food supply could be in jeopardy as global warming intensifies, the report warns. Crop yields for corn, wheat and soy tend to decline as the number of extremely hot days increases. More frequent droughts could reduce supplies of irrigation water. Dairy cows produce less milk in the sweltering heat.
Farmers will have to rethink their practices in response.
In areas at risk of drought, they could use more precise irrigation techniques to conserve water. Agricultural regions could build new weather networks that provide more detailed climate forecasts, to help farmers make better decisions about which crops to plant, and when. In places like the Great Plains, dairy farmers and ranchers may need to relocate production or invest in climate-controlled buildings to protect their cattle from heat stress.
But the report emphasizes, “these approaches have limits under severe climate change impacts.”
One hope is that seed companies might develop new crop varieties that are better able to tolerate drought, heat waves and pests. However, the report cautions that “progress in this area has been modest” and calls for much greater public investment.
2. Build for the future, not the past
Much of the nation’s infrastructure, including things like roads and sewers, was built with historical weather conditions in mind. But as extreme weather becomes more frequent, the report says, the past is no longer a good guide to the future.
In Hampton Roads, Va., nearly half of residents reported being unable to drive out of their neighborhoods at some point last year because of flooding at high tide as sea levels have risen. In the Northeast, sewer systems built for the storms of the past are expected to overflow more frequently as climate change brings heavier rainfall.
“It’s still not standard practice for engineers to think about future climate,” said Costa Samaras, an associate professor of civil and environmental engineering at Carnegie Mellon University. While a few cities, like New York and Baltimore, have begun using climate forecasts in their infrastructure planning, he said, “it’s not as widespread as it needs to be.”
3. Retreat from the coasts
Depending on how rapidly emissions increase, global sea levels are likely to rise between 1 and 4 feet (or even more) this century, the report says, potentially putting trillions of dollars’ worth of coastal homes and businesses in the United States at risk of flooding.
While large cities like New York and Boston will likely invest heavily in sea walls, tide gates and pumping stations, they won’t be able to protect everyone. In places like Norfolk, Va., officials are already pondering the prospect of relocating certain vulnerable neighborhoods.
Ultimately, the report warns, millions of people nationwide may have to move away from the coasts. Yet most policymakers are reluctant to even broach the topic. Many local governments, in search of more tax revenue, still promote development along coastlines. And a bevy of federal policies, such as subsidized flood insurance and efforts to rebuild communities in place after disasters, still discourage people from moving away from at-risk areas.
Katherine Greig, a senior fellow at the Wharton Risk Center and co-author of the report’s chapter on adaptation, said that “We’re still a long ways” from having “a serious conversation about retreat.”
4. Enlist nature to help
Climate adaptation isn’t just a matter of redesigning roads or power plants to be more resilient to extreme weather. The report also details ways that our natural environment, if managed properly, can be a cost-effective defense against climate change.
Planting more trees in cities can help reduce urban temperatures and protect people from deadly heat waves. Restoring degraded wetlands and marshes can protect cities and coasts from flooding and improve water quality. Healthy forests that are allowed to burn at a low level periodically, as they did in the distant past, are less prone to extreme wildfires. Protecting pollinators could help make our agricultural system more resilient.
One example from the report: Several Midwestern cities, including Milwaukee, have begun a large-scale effort to restore streams to their natural state, removing concrete linings, so that they can safely carry away more water during heavy storms.
5. Expect the unexpected
As detailed as the new 1,656-page climate assessment is, the authors still warn that global warming is likely to bring unpredictable dangers, particularly as complex systems like energy, water, transportation and public health all come under severe stress at once.
As an example, Hurricane Harvey in Texas last year ended up shutting down gasoline refineries, straining hospitals, clogging roadways and spreading toxins and pathogens as floodwaters swamped the city. These sorts of “cascading failures” are difficult to study and predict in advance.
At a broad level, the report warns that officials at every level of government and in every corner of the economy will have to weave climate change into their decisions, to plan for a wide range of possible futures, and to continually re-evaluate those plans. “Adaptation entails a continuing risk management process,” the report notes. “It does not have an end point.”
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