From heat waves to wildfires to floods, U.S. EPA and its allies last week painted a dire picture of climate change impacts that they say justify the survival of the Clean Power Plan.

EPA described greenhouse gas emissions as “a monumental threat” in court filings defending President Obama’s signature climate rule for the nation’s power sector. The agency argues that climate change will lead “to an array of severe negative effects, which will worsen over time.”

“These effects include rising sea levels that could flood coastal population centers; increasingly frequent and intense weather events such as storms, heat waves, and droughts; impaired air and water quality; shrinking water supplies; the spread of infectious disease; species extinction; and national security threats,” EPA wrote in a brief filed with the U.S. Court of Appeals for the District of Columbia Circuit.

The Clean Power Plan is being challenged by 27 states and multiple industry groups that claim EPA overstepped its authority when establishing the climate rule. These parties scored a victory in February when the U.S. Supreme Court announced a stay of the rule.

EPA’s filing last week shows that the administration might see legal advantages in highlighting potential climate impacts to society. The thrust of its defense still resides in convincing the court that the agency properly established the rule within the scope of the Clean Air Act.

The Obama administration has long argued climate change is already harming the United States. That’s a key message in its most recent National Climate Assessment. The administration argues that this justifies a series of federal regulations to curb greenhouse gas emissions. It’s also a centerpiece of the administration’s participation in an international climate agreement forged last year in Paris.

In a wave of briefs filed with the D.C. Circuit last week ahead of a court deadline, many of the rule’s supporters also provided anecdotes to bolster the administration’s message.

“We are so dependent on agriculture and farmers are such an important part of our state economically and culturally in every way, and climate change presents enormous problems for farmers, particularly in terms of the temperatures,” Iowa Attorney General Tom Miller (D), an intervenor in the case, said during a press call.

Miller noted that while temperatures are “pretty close to ideal in Iowa right now, that could change dramatically over time.”

An amicus brief filed by the U.S. Conference of Mayors and the National League of Cities presented a long list of damaging events cities are attributing to climate change.

“Mayors know cities have the most to gain, as well as the most to lose in this debate because climate change and rising sea levels threaten the physical structure of our cities,” Baltimore Mayor Stephanie Rawlings-Blake, who’s president of the U.S. Conference of Mayors, said in a statement.

The brief stated, “Consider San Francisco, where not just neighborhoods, but also port facilities, highways, wastewater treatment plants, and runways at two major airports are under regular and growing threat from rising seas.”

“News of heat wave-related deaths and hospitalizations has become a tragic annual event in American cities, with impacts felt in Baltimore, Chapel Hill, Dallas, Minneapolis, Portland (Oregon), Providence, and Reno, to name but a few affected cities,” the brief added. “Furthermore, heat waves often do costly damage to water, transportation, and electricity infrastructure as well as to human health.”

Climate attribution is sometimes fuzzy

A group of national medical and health professional organizations also warned of climate change’s impact on public health in a separate brief.

“Direct impacts from the changing climate include heat-related illness, declines in air quality, and increased respiratory and cardiovascular illness,” it says, adding, “The extreme weather expected to occur alongside climate change may lead to injury, disability, and death.”

Members of Congress who filed a “friend of the court” brief last week also laid out disastrous weather events affecting their constituencies in a press call Friday.

“Those of us in California are dealing with record-setting wildfires across the West and drought more severe than anything we’ve ever seen,” said Rep. Jared Huffman (D-Calif.).

In the science community, however, attributing individual natural disasters to man-made greenhouse gas emissions is a tricky and controversial topic.

A recent report by the National Academy of Sciences determined that while climate change is a clear culprit behind heat waves and cold snaps, the body of scientific literature is only moderately certain it’s behind drought and extreme rainfall events. The report found there is even less certainty that climate change is a significant driver of events like thunderstorms, wildfires or cyclones (ClimateWire, March 14).

A number of climate scientists, including the Carnegie Institution for Science’s Ken Caldeira, Stanford University’s Noah Diffenbaugh, Princeton University’s Michael Oppenheimer and the University of Arizona’s Jonathan Overpeck, also filed a friend of the court brief Friday defending the Clean Power Plan.

“As practicing scientists who study the Earth’s climate, we — and many in our profession — have long recognized that human emissions of greenhouse gases (primarily carbon dioxide, but also methane, nitrous oxide, and fluorocarbons) can significantly change the Earth’s climate,” the brief states.

“The extent to which we have already been observing the ongoing impacts of human-caused climate change has led us to participate in this case right now,” it continues. “We are observing increasing global temperatures; shifting plant and animal ranges; worsening droughts; global retreat of glaciers and ice sheets; shrinking Arctic sea ice; rising sea levels; acidification of our oceans; and many other serious impacts of global climate change. These phenomena are all directly connected to our human alteration of the atmosphere.”

Many of the Clean Power Plan’s most ardent foes believe the science behind climate change is uncertain, downplaying or disputing evidence that it poses any threat at all.

Among them are Oklahoma Attorney General Scott Pruitt (R) and Alabama Attorney General Luther Strange (R), who last week said in a joint statement that “reasonable minds can disagree about the science behind global warming, and disagree they do.”