WASHINGTON • A major scientific report issued by 13 US federal agencies presents the starkest warnings to date of the consequences of climate change for the United States, predicting that if significant steps are not taken to rein in global warming, the damage will knock as much as 10 per cent off the size of the US economy by the century's end.
Friday's report, which was mandated by Congress and made public by the White House, is notable not only for the precision of its calculations and bluntness of its conclusions, but also because its findings are directly at odds with President Donald Trump's agenda of environmental deregulation, which he asserts will spur economic growth.
Mr Trump has taken aggressive steps to allow more planet-warming pollution from vehicle tailpipes and power-plant smokestacks, and has declared he will pull the US out of the Paris Agreement, under which nearly every country in the world pledged to cut carbon emissions.
Just last week, he mocked the science of climate change because of a cold snap in the North-east, tweeting: "Whatever happened to Global Warming?"
The 1,656-page assessment lays out the devastating effects of a changing climate on the economy, health and environment, including record wildfires in California, crop failures in the Midwest and crumbling infrastructure in the South.
Going forward, American exports and supply chains could be disrupted, agricultural yields could fall to 1980s levels by mid-century and fire season could spread to the south-east, the report finds.
All told, the report says, climate change could slash up to a tenth of gross domestic product by 2100, more than double the losses of the Great Recession a decade ago.
What the US economy risks facing if no significant steps are taken to rein in global warming:
Labour-related losses annually by 2090 as a result of extreme heat, which makes it difficult for people to work outdoors or seriously lowers productivity.
Economic toll per year in 2090 due to deaths from temperature extremes.
Yearly coastal property damage from rise in sea levels.
Infrastructure damage by the end of the century.
"This report will weaken the Trump administration's legal case for undoing climate change regulations and it strengthens the hands of those who go to court to fight them," said Dr Michael Oppenheimer, a professor of geosciences and international affairs at Princeton.
The report is the second volume of the National Climate Assessment, which the federal government is required by law to produce every four years.
The previous report, issued in May 2014, concluded with nearly as much scientific certainty, but not as much precision on the economic costs, that the tangible impacts of climate change were already causing damage across the country. It cited increasing water scarcity in dry regions, torrential downpours in wet regions and more severe heat waves and wildfires.
Questioning the accuracy of the latest report, White House spokesman Lindsay Walters said it was "largely based on the most extreme scenario, which contradicts long-established trends by assuming that... there would be limited technology and innovation, and a rapidly expanding population".
The government's next update of the National Climate Assessment, she said, "gives us the opportunity to provide for a more transparent and data-driven process that includes fuller information on the range of potential scenarios and outcomes".
The findings come a month after the Intergovernmental Panel on Climate Change, a group of scientists convened by the United Nations, issued its most alarming and specific report to date about the severe economic and humanitarian crises expected to hit the world by 2040.
But the new report also emphasises that the outcomes depend on how swiftly and decisively the US and other countries take action to mitigate global warming.
"Future risks from climate change depend primarily on decisions made today," it said.