The authors of the Fourth National Climate Assessment pulled no punches in issuing a dire warning regarding the inevitable consequences of leaving the rapid progression of global warming unchallenged. The report predicts that the United States economy will suffer an annual loss of hundreds of billions of dollars, along with the loss of thousands of American lives, every year by the end of the century, as the direct result of the effects of climate change.

"Earth’s climate is now changing faster than at any point in the history of modern civilization, primarily as a result of human activities," according to the National Climate Assessment’s opening sentence. "The assumption that current and future climate conditions will resemble the recent past is no longer valid.

"The impacts of climate change are already being felt in communities across the country. More frequent and intense extreme weather and climate-related events, as well as changes in average climate conditions, are expected to continue to damage infrastructure, ecosystems, and social systems that provide essential benefits to communities."

Indeed, within the last two months alone, two towns in the United States have disappeared from the face of the Earth: Mexico Beach, FL, washed away by the winds and storm surge of record-breaking hurricane Michael in October; and Paradise, CA, was razed to the ground by the also record-setting Camp Fire in November. Both events were exacerbated into becoming deadly, record-breaking events by the effects of global warming.

The National Climate Assessment is an interagency report produced by the US government every four years, as mandated by the Global Change Research Act of 1990, itself a collaboration between thirteen agencies and departments, including NASA, NOAA, and the Department of Defense. This year’s report, released on November 23, is the result of the efforts of over 300 authors, with the contributing scientists condensing the accumulated knowledge of thousands of studies into the report.

The report details the predicted impacts that will be suffered by the US on a number of levels, including areas such as the economy, public health, agriculture, infrastructure, clean water availability, ecology and ecological services, and America’s Indigenous peoples.

"In the absence of significant global mitigation action and regional adaptation efforts, rising temperatures, sea level rise, and changes in extreme events are expected to increasingly disrupt and damage critical infrastructure and property, labor productivity, and the vitality of our communities," the report warns. The report also predicts that, "annual losses in some economic sectors are projected to reach hundreds of billions of dollars by the end of the century—more than the current gross domestic product (GDP) of many U.S. states."

The number of heat-related deaths is expected to rise, along with deaths resulting from the spread of insect-borne diseases, such as Lyme disease, and the Zika, West Nile, and dengue viruses, as regional shifts in climate promote the spread of tics and mosquitoes into new areas. This is also to say nothing of the more direct fatalities from the effects of storms, flooding, and wildfires.

"Climate change and extreme weather events are expected to increasingly disrupt our Nation’s energy and transportation systems, threatening more frequent and longer-lasting power outages, fuel shortages, and service disruptions, with cascading impacts on other critical sectors," including basic necessities such as food delivery, water and waste management, and the access of emergency response workers to affected areas.

Although the report concedes that some regions might see increased agricultural productivity from the effects of global warming, "overall, yields from major U.S. crops are expected to decline as a consequence of increases in temperatures and possibly changes in water availability, soil erosion, and disease and pest outbreaks." Extreme heat effects are also expected to adversely impact livestock, and are expected to be the largest contributing factor to declines in the productivity of U.S. agriculture," especially in the US Midwest.

Despite the dire warnings issued by the National Climate Assessment, it also offers advice on how to both mitigate and adapt to the effects of global warming. In regards to social systems, the report offers that "joint planning with stakeholders across sectors, regions, and jurisdictions can help identify critical risks arising from interaction among systems ahead of time."

Impacts on agriculture could be mitigated by "altering what is produced, modifying the inputs used for production, adopting new technologies, and adjusting management strategies"; "Forward-looking infrastructure design, planning, and operational measures and standards can reduce exposure and vulnerability to the impacts of climate change…"; and that "Indigenous peoples are taking steps to adapt to climate change impacts structured around self-determination and traditional knowledge, and some tribes are pursuing mitigation actions through development of renewable energy on tribal lands."

The report also points out that any efforts made toward addressing climate change are likely to have beneficial side effects. "Mitigation and adaptation actions also present opportunities for additional benefits that are often more immediate and localized, such as improving local air quality and economies through investments in infrastructure. Some benefits, such as restoring ecosystems and increasing community vitality, may be harder to quantify."