An urgent warning on climate

U.S. report: Far-reaching effects if emissions are not quickly curbed

A new report by the federal government says climate change’s effects are intensifying across the country, unleashing more severe droughts, more dangerous heat waves, and bigger and more destructive wildfires.

The report summarizes the latest scientific research on the effects of global warming that are happening now. It further addresses the far-reaching effects on Americans’ lives — including the expected consequences for people’s health and the nation’s economy — that are projected in coming years if the world doesn’t act quickly to reduce greenhouse-gas emissions.

In the Southwest, the report’s authors said, higher temperatures are amplifying drought across the Colorado River Basin. They said climate change is making the Southwest drier and diminishing water supplies, posing a major risk for agriculture in a region that produces much of the country’s food.

“Increased temperatures, especially the earlier occurrence of spring warmth, have significantly altered the water cycle in the Southwest region,” the authors wrote in the report. “These changes include decreases in snowpack and its water content, earlier peak of snow-fed streamflow, and increases in the proportion of rain to snow.”

They said those changes are attributed mainly to climate change and are leading to a drying trend.

Higher temperatures evaporate more water off the landscape, dry out soils and shrink the amount of runoff from rain and snow that makes its way into streams and rivers.

“For the same amount of snow falling, we’re getting less bang for the buck,” said Gregg Garfin, a University of Arizona climate scientist who co-authored the chapter on the Southwest. “All of that, based on the climate projections, really says that we’re drying out, and that it would take much more precipitation for us to counteract the effects of that drying.”

Other takeaways, Garfin said, include that during the past several years an array of cities, states and other groups “have made modest, incremental advances to adapt to climate change.”

“While much more can and needs to be done, we can take heart in small successes,” Garfin said, “and look upon them as motivation to multiply efforts to adapt to change, and to reduce greenhouse-gas emissions.”

Questions about report’s timing

The report, the “Fourth National Climate Assessment Volume II: Impacts, Risks, and Adaptation in the United States,” was released Friday by the federal government. Thirteen federal agencies are involved in the U.S. Global Change Research Program, which releases the periodic reports, and outside scientists and experts participated in drafting the report. It was written by more than 300 authors and includes more than 5,500 scientific references.

The report was prepared before this year’s devastating wildfires in California, including the state’s deadliest wildfire in history. But it said research shows climate change is leading to increases in the areas burned by wildfires.

“Analyses estimated that the area burned by wildfire across the western United States from 1984 to 2015 was twice what would have burned had climate change not occurred,” the researchers wrote. They said cuts in greenhouse-gas emissions, changes in forest management and other actions can help reduce risks.

The report was released by the government two days after President Donald Trump, who has called climate change a “hoax,” tweeted about a “Brutal and Extended Cold Blast” and said: “Whatever happened to Global Warming?”

The decision to make the findings public on the Friday after Thanksgiving prompted questions from critics, who said the timing seemed geared toward ensuring that news of the report would get less attention.

The authors laid out in detail how the planet has been getting warmer over the past century. They said global average temperature has increased about 1.8 degrees Fahrenheit from 1901 to 2016 and that “the evidence consistently points to human activities, especially emissions of greenhouse or heat-trapping gases, as the dominant cause.”

As for the future, the researchers said average global temperatures, without significant reductions in emissions, could increase by 9 degrees Fahrenheit or more by the end of this century. If there are significant reductions in greenhouse gases, they said, the temperature increase could be limited to 3.6 degrees Fahrenheit.

“Global average temperature is much higher and is rising more rapidly than anything modern civilization has experienced,” said David Easterling of the National Oceanic and Atmospheric Administration. “And this warming trend can only be explained by human activities, especially emissions of greenhouse gases into the atmosphere.”

Easterling summarized the report’s key points in a conference call with reporters, saying that sea-level rise increasingly threatens coastal regions and that extreme weather events are projected to bring “greater risks of infrastructure disruption and failure that can cascade across economic sectors.”

“Climate change presents growing challenges to the economy and our nation’s infrastructure, the natural environment and services ecosystems provide to society, and human health and quality of life,” Easterling said.

“The continued warming that is projected to occur without significant reductions in global greenhouse gas emissions is expected to cause substantial net damage to the U.S. economy, especially in the absence of increased adaptation efforts,” he said.

He said by the middle of the century, “how much the climate changes will depend primarily on global emissions of greenhouse gases and on the response of the climate system to this human-induced warming.”

Easterling said global-scale reductions in greenhouse-gas emissions would help reduce the risks of climate change, and that in the past several years a growing number of cities, states and businesses have taken initiatives to help. However, he said, “these efforts do not yet approach a scale needed to avoid substantial damages to the economy, the environment and human health expected over the coming decades.”

Climate scientist Katharine Hayhoe of Texas Tech University said on Twitter that when it comes to climate change, the most dangerous myth that some people have bought into is a sense that “it doesn’t matter to ME.”

She said the report “tackles this myth head-on, showing how climate change is already affecting each one of us, whether we live in Texas or Minnesota or Hawai’i or Florida.”

“Those who are already vulnerable are those who will suffer the most,” Hayhoe wrote. “Cutting carbon emissions (e.g., through global actions such as the Paris Agreement) will substantially reduce these risks to people in the U.S. and around the world. The good news is that we’re actually moving in the right direction: but the bad news is, it’s not nearly fast enough.”

The authors wrote in the report that people who are already vulnerable, “including lower-income and other marginalized communities, have lower capacity to prepare for and cope with extreme weather and climate-related events.” The researchers pointed to health threats posed by hotter temperatures, including worsening heat waves that have taken a deadly toll in Arizona and California in recent years.

They said climate change is projected to expose more Americans to ticks that carry Lyme disease, and to mosquitoes that transmit the West Nile, dengue and Zika viruses. They also said the warming “may weigh heavily on mental health in the general population and those already struggling with mental health disorders.”

As for water supplies, the authors said groundwater depletion is worsening drought risks in many parts of the United States, particularly in the Southwest and Southern Great Plains, and that the dwindling Colorado River — and the dropping levels of Lake Powell and Lake Mead — “increases the risk of water shortages across much of the Southwest.”

Less water, they said, could ultimately translate into a big hit for agriculture and the country’s food supply.