Human-triggered climate change is touching every region of the United States in some way, and effects are projected to intensify if greenhouse-gas emissions aren't reduced and eventually brought to zero, according to a comprehensive report on climate change in the US released Monday.
The report is the third in a congressionally mandated effort to give lawmakers and policymakers periodic updates on what the latest climate research shows about current conditions and projected effects from global warming.
Like the recent volumes from the United Nations-backed Intergovernmental Panel on Climate Change (IPCC), the National Climate Assessment for 2014 points to indicators of change in the face of rising atmospheric greenhouse-gas concentrations. These indicators vary in mix and intensity by region, as they do globally.
Among the effects: increased flooding vulnerability for low-lying coastal areas, related to sea-level rise; more frequent and intense droughts, particularly in the Southwest, and longer, hotter heat waves in several other regions; and heavier rain dropping on the upper Midwest and the Northeast during the most-intense storms. Effects of ocean acidification are growing more apparent off the US Northwest.
The report, produced by the Obama administration, is "unprecedented" in its comprehensiveness and detail in describing how climate change is affecting regions of the US and different sectors of the economy now, and how those effects are projected to intensify, especially if emissions follow a business-as-usual path, said John Holdren, President Obama's science adviser, during a briefing Monday.
For the first time, the report includes detailed chapters on adaptation and mitigation. This mirrors an increased emphasis in the IPCC volumes on adaptation and on reducing the climate risk facing people, their homes, and the airports, highways, causeways, pipelines, and other infrastructure their economies require.
The report "has a lot of actionable information about how planners, decisionmakers, farmers, fishermen, foresters, and indicidual citizens can take actions to reduce the damage" from climate change, Dr. Holdren said.
In the adaptation arena, progress in some regions of the US to find ways to increase resilience to climate change leaves room for what University of Arizona geoscientist Gregg Garfin dubs apocol-optimism.
"The real sliver lining in this is that this issue has gotten the attention of our planners, public-health officials, water managers, and our citizens," says Dr. Garfin, one of two researchers who oversaw the chapter dealing with the US Southwest. "They're waking up to these threats, and they're developing plans to prepare and reduce risks."
Even so, the report notes that "strenuous effort" will be needed to help put global emission-reduction efforts on a path that would hold the rise in global average temperatures by the end of the century to about 2 degrees Celsius (3.6 degrees Fahrenheit).
In the US, carbon-dioxide emissions fell by 9 percent between 2008 and 2012, driven largely by the Great Recession and greater use of natural gas rather than coal to generate electricity. Yet such gains, which largely occurred without any specific climate policy to direct them, are included in business-as-usual emissions scenarios.
The strenuous effort is not there, says Jacob Jacoby, professor emeritus at the Massachusetts Institute of Technology's Sloan School of Economics and one of two researchers who directed the chapter on mitigation.
"People say: We're doing nothing. We're not doing nothing. There's a lot going on in the cities, a lot going on voluntarily. California is doing a lot, as much as anybody in the world," he says. "But the scale of what's being done in terms of emissions is not enough to turn the corner."
Environmental groups see the report as a another call to action.
“Our leading scientists send a stark message: Climate change is already seriously disrupting our lives, hurting our health and damaging our economy,” said Frances Beinecke, president of the Natural Resources Defense Council, in a prepared statement. Reducing carbon emissions "is a win-win: It can create thousands of jobs, expand energy efficiency and lower electric bills while improving public health. That’s the climate legacy we can, and must, leave future generations.”
Others were less enthusiastic.
“Facing a recovering, yet fragile, economy, with families across the country struggling to make ends meet, it is concerning that the Obama administration is busy promoting its politically driven climate change agenda, instead of addressing the real issues plaguing our nation,” said Laura Sheehan, senior vice president for communications of the American Coalition for Clean Coal Electricity, in a statement.
The report may not sway skeptics who doubt the science behind global warming, given their religious faith or their political ideology, or the proposed solutions, suggests Katharine Hayhoe, a researcher at Texas Tech University in Lubbock and one of the lead authors of the chapter on climate-change science.
As for additional federal action to curb emissions, "we've got a challenging context on Capitol Hill," Holdren acknowledged. "That's why the president is determined to move forward under the climate action plan" – an effort the White House unveiled last June that relies on his executive authority to cut US greenhouse-gas emissions.
Instead, the report is aimed at people who believe the problem is a distant one.
"For the vast majority that feel that climate change may be an issue, but it's an issue that we're going to worry about later, or it doesn't matter to me, ... or it's not on my Top 10 priority list, for those this report really matters," she says. "This report shows how climate is changing here and now and it matters to each one of us, no matter what part of the country we live in."
Since the last report in 2009, one region has emerged with projected effects that in some ways are counterintuitive.
For all its moss-draped greenery, intensifying rainstorms, and encounters with tropical cyclones and their remnants, the Southeast could be headed for significant water woes from climate change if emissions continue on a business-as-usual trajectory, according to Kirstin Dow, a geography professor at University of South Carolina in Columbia, S.C., and a lead author on the chapter identifying additional research needs for these climate assessments.
"Our water-resource situation is a major concern," she says. An expanding population and changing land-use patterns to accommodate the increase are expected to collide with a greater likelihood of multi-season droughts in parts of the region.
Moreover, by midcentury, projections indicate that the Southeast is likely to face 30 to 50 more days a year with temperatures topping 95 degrees F.
Along with hot conditions – especially dry conditions in drought years – the threat of wildfires looms.
"We actually lead the nation in the number of wildfires," she says of the region. "And that number is continuing to increase."
These come atop the risk the region's coastal areas face from rising sea levels and, in particular, the storm surges that tropical cyclones can drive ashore.
The open question is whether this report will stimulate additional public and political action, given its more-detailed regional assessments.
"If you look at the polling, they get the fact that it's caused by human activity, particularly the burning of fossil fuels. They get and support the solutions to climate change. But they don't feel that sense of urgency. I think this report can help influence that," said White House counselor John Podesta.
[Editor's Note: An earlier version of this article misstated Kristin Dow's affiliation. She is a professor at the University of South Carolina in Columbia, S.C.]