NCA 4: Impacts, Risks, and Adaptation in the United States (Volume II)

Below are highlights from Volume II of the 4th U.S. National Climate Assessment by the U.S. Global Change Research Program, published on November 23, 2018. For key excerpts, see here.

Report Highlights

Human activity, primarily burning fossil fuels, is causing climate change. There is no credible alternative to global warming emissions to explain the warming.

• Global average temperatures have risen 1.8°F (1.0°C) since 1901, predominantly because of human activity, especially the emission of heat-trapping gases.
• Globally, 16 of the last 17 years are the warmest years on record.
• Depending on the region, Americans could experience an additional month to two month’s worth of days with maximum temperatures above 100°F (38°C) by 2050, with that severe heat becoming commonplace in the southeast by 2100.

Economic losses from climate change are significant for some sectors of the U.S. economy.

• In some sectors, losses driven by the impacts of climate change could exceed $100 billion annually by the end of the century.
• If emissions continue unabated, extreme temperatures could end up costing billions upon billions in lost wages annually by the end of the century, and negatively impact the health of construction, agricultural and other outdoor workers.
• Many aspects of climate change – including extreme heat, droughts, and floods – will pose risks to the U.S. agricultural sector. In many places, crop yields, as well as crop and grazing land quality, are expected to decline as a result.
• We may be underestimating our level of risk by failing to account for multiple impacts occurring at once, or not planning for impacts that will span across government borders and sector boundaries.
• Our aging infrastructure, especially our electric grid, will continue to be stressed by extreme weather events, which is why helping communities on the frontlines of climate impacts to adapt is so crucial.

Americans are already responding to the climate change impacts of burning fossil fuels.

• Increased global warming emissions have contributed to the observed increases in Atlantic hurricane activity since 1970.
• Climate change doubled the area burned by wildfires across the West between 1984 and 2015, relative to what would have burned without warming. Climate change was a greater factor in area burned between 1916 and 2003 than was fire suppression, fire management or non-climate factors.
• By 2100, annual acreage burned by wildfires could increase by as much as 6 times in some places. The U.S. spends an average of about $1 billion annually to fight wildfires, but spent over $2 billion in 2015 due to extreme drought. Costs exceeded $2 billion in the first 8 months of 2017.
• The U.S. military is already working to understand the increased risks of security issues resulting from climate change-induced resource shocks (droughts causing crop failure, for example, which can contribute to civil unrest) as well as extreme weather events and direct impacts on military infrastructure, like sea level rise or extreme heat at military bases.

Storm surge and tidal flooding frequency, depth and extent are worsened by sea level rise, presenting a significant risk to America’s trillion-dollar coastal property market.

• Global sea level has risen about 8-9 inches since 1880, 3 inches of which have come since just 1993. We can expect at least several inches more in the next 15 years, with 1-4 feet very likely by 2100, and as much as 8 feet physically possible by 2100.
• Sea level rise has already increased the frequency of high tide flooding by a factor of 5 to 10 since the 1960s for some U.S. coastal communities.
• Climate change is already hurting coastal ecosystems, posing a threat to the fisheries and tourism industries as well as public safety and human health. Continuing coastal impacts will worsen pre-existing social inequities as vulnerable communities reckon with how to adapt.

Every American’s health is at risk from climate change, with the elderly, young, working class and communities of color being particularly vulnerable.

• Reducing greenhouse gas emissions will, by the end of the century, potentially save thousands of lives annually, and generate hundreds of billions of dollars of health-related economic benefits compared to a high emissions scenario.
• Allergies like hay fever and asthma are likely already becoming more frequent and severe.
• Warmer temperatures are expected to alter the range of mosquitoes and ticks that carry vector-borne diseases like Zika, West Nile virus, dengue, chikungunya and yellow fever.
• Drier conditions in Arizona and California have led to greater growth of the fungus that leads to Valley Fever (coccidioidomycosis) while Cryptococcal infections were strictly tropical before 1999, but have moved northward, with Oregon experiencing 76 cases in 2015.
• West Nile is projected to double by 2050, with a $1 billion annual price tag.

Transitioning from fossil fuels to renewable energy sources will reduce the risks of climate impacts.

• A certain amount of warming is likely “locked in” so adaptation is still required.
• The faster we reduce global warming emissions, the less risk we face and the cheaper it will be to adapt.