Climate change altering U.S. in profound ways, major report finds

A sweeping new federal report finds the effects of climate change are increasingly evident across the U.S., from the Florida Keys to Alaska, and argues for transformational adaptation policies and steep emissions cuts.

Driving the news: The Fifth National Climate Assessment (NCA5) shows how warming is rippling across regions and economic sectors, and emphasizes the steps governments are already taking to better adapt.

• The report is likely to bolster the U.S.'s case for its own climate policies and the need for further actions at the upcoming COP28 summit in Dubai.
• "Overall, we expect climate change to significantly impact the economic opportunities of nearly all American families — affecting their income, what they spend to maintain their standard of living, and the value of their assets, particularly real estate," said Solomon Hsiang of UC Berkeley, the lead author of the economics chapter.

Why it matters: The congressionally-mandated report is the most complete and authoritative look yet at U.S. climate change impacts and responses. It's the product of hundreds of authors from 13 federal agencies and academic experts.

• The science assessment is the first since 2018, when the Trump administration released the fourth edition on Black Friday to minimize publicity.

Zoom in: The assessment comes with a suite of tools that its authors hope will be useful for local officials, federal agencies and journalists, allowing people to explore the influence of climate change, as well as policy actions, down to the local level.

• It also calls attention to the inequities of this issue and how minorities and other marginalized communities continue to suffer more severe consequences.

Yes, but: While this report could prove influential and useful for decision makers, it does not contain major new revelations. Rather, it shows how climate change has proceeded, and in many cases even sped up, since 2018.

• It connects the dots to reveal a country already significantly altered despite the relatively low amount of global climate change so far (about 1.2°C (2.16°F) above the preindustrial era).

Between the lines: The assessment finds the economic impacts of climate change could shake everything from U.S. financial markets to global supply chains, and even household budgets as homes exposed to climate impacts, such as "sunny day" flooding are seeing lower values compared to identical property nearby.

• "Estimates of nationwide impacts indicate a net loss in the economic well-being of American society," the report warns.
• The assessment notes the "growing concern" about systemic risk to financial stability from cascading climate impacts.
• It also emphasizes the net economic benefits of transitioning energy systems from fossil fuels to one largely powered by renewables.

The intrigue: The assessment shows how climate change is affecting each region of the country.

• In the Northeast, for example, it notes that extreme precipitation events have increased by about 60%, for the largest increase in the country.
• In the Southwest, it notes that between 1913 and 2017, annual average Colorado River discharge decreased by 9.3% for each degree Celsius of warming.
• The U.S. overall is warming faster than the global average, and the state that is transforming the most is Alaska, the report finds, noting the "world's highest rates of ocean acidification" there, along with "extreme climate-related changes" overall.

• Notably, it finds that not only is the U.S. the biggest historical emitter of greenhouse gases, but that when accounting for all such pollutants (including methane and others in addition to CO2), the U.S. alone is responsible for 17% of current global warming.

What they found: The NCA5 authors were able to narrow the range of expected warming that the U.S. will see in coming decades — but it is higher than the previous assessment, said Ruby Leung, a climate scientist at Pacific Northwest National Laboratory and lead author of the NCA5's chapter on Earth systems, in an interview.

• The new report pegs this warming at between 4.5°F and 7.2°F, which would result from a doubling of CO2 concentrations in the atmosphere.
• For NCA4, the likely range of temperature increase was wider, at between 2.7°F to 8.0°F.
• "It is now virtually certain that the warming from a doubling of atmospheric CO2 is greater than 2.7°F, guaranteeing significant climate change impacts from ongoing increases in CO2 and other greenhouse gases," Leung told Axios.

Context: The report lands in the midst of what is nearly certain to be the hottest year on record globally, with a spate of extreme weather events that have shattered records across both hemispheres.

• NCA5 went through multiple rounds of peer review by federal experts, external panels, and the public throughout its development process.

The bottom line: "All of our future projections are conditional on the emissions scenario: if we don't want the world to warm by 3°C or 4°C, we know what to do," said Kate Marvel, a chapter lead author of the NCA5.