Climate related impacts are already being felt, and are expected to worsen across all sectors of our communities. Many impacts specific to regions of the United States have been documented in the U.S. Global Change Research Program’s 2014 National Climate Assessment.

Some examples of expected impacts include:

Impacts on Society

• Population shifts and development choices are making more Americans vulnerable to heat waves, wildfire, drought, and severe storms, all of which are expected to become more common with climate change.
• Climate change vulnerability is greater for those who have few resources and few choices – those who can least afford to deal with the impacts.
• City residents and city infrastructure are highly vulnerable to impacts from heat and flooding.
• Communities will be affected by local changes in climate, as well as change throughout the nation and abroad, due to our global economy.
• Insurance is one of the industries particularly vulnerable to increasing extreme weather events such as severe storms, but it can also help society manage the risks. Insurance companies have a sound understanding of climate change science and the related risks. 
• Many Native American tribes are highly vulnerable to the impacts of climate change because of their close links to natural systems for subsistence food and cultural traditions. Those in Alaska have the additional stressors from melting ice and permafrost that cause dangerous conditions for infrastructure and transportation.

Ragweed pollen season length has increased in central North America between 1995 and 2011 by as much as 11 to 27 days in parts of the U.S. and Canada in response to rising temperatures. From the National Climate Assessment 2014.

Impacts on Human Health

• Warming increases the formation of ground-level ozone, which can cause respiratory and heart disease.
• Extreme weather events cause physical and mental health problems. Extreme events have already increased, and are expected to become even more frequent and more severe.
• Many diseases transmitted by food, water, and insects are likely to increase with warmer temperatures.
• Rising temperature and carbon dioxide concentration increase pollen production and prolong the pollen season in a number of plants with highly allergenic pollen, presenting a health risk.
• Smoke from wildfires can reduce air quality, causing impacts to those with asthma and respiratory disease.
• Certain groups, including children, the elderly, and the poor, are most vulnerable to a range of climate-related health effects.
• Native Alaskans and are at risk of health-related impacts as traditional subsistence foods become scarce and are replaced by packaged foods.

Impacts on Ecosystems

• Ecosystem processes, such as those that control plant growth and decomposition, have already been affected by climate change.
• Plants and animals have already experienced shifts in distribution and timing. These shifts are unlikely to be able to keep up with the speed of climate change expected in the future.
• Models project that 30-50% of all species could become extinct from climate change, by the end of this century.
• Insect pests, disease pathogens, and invasive weed species have increased, and these trends are likely to continue.
• Deserts and dry lands are likely to become hotter and drier, feeding a self-reinforcing cycle of invasive plants, fire, and erosion.
• Coastal and near-shore ecosystems are expected to be lost in many areas as the sea level rises.
• Ocean acidification will result in the loss of many marine species.
• Some species are highly vulnerable to climate change, including those at high elevations, in cold-water rivers and streams, and those with very limited ranges or specialized conditions.
• Riparian and wetland species are highly vulnerable in areas that are expected to become more arid.

As air and water temperatures rise, marine species are moving northward, affecting fisheries, ecosystems, and coastal communities that depend on the food source. On average, by 2006, the center of the range for examined species moved 19 miles north of their 1982 locations. From the National Climate Assessment 2014.

Projected changes in dominant tree species throughout the Eastern U.S., from 1960-2100. From the National Climate Assessment 2009.

Impacts on Agriculture

• Many crops show positive responses to elevated carbon dioxide and low levels of warming, but higher levels of warming will negatively affect growth and yields. Food production could become stressed.
• Extreme events such as heavy downpours and droughts are already reducing crop yields and are likely to have even greater impacts over time.
• Weeds, diseases, and insect pests benefit from warming and higher CO2 levels. Greater pesticide use could result in more pollution and negative impacts to human health.
• Increased heat, disease, and weather extremes are likely to reduce forage and livestock productivity. This could also affect food prices.

Projected changes in California crop yields over the next century, based on a continued high emissions scenario (A2 in red) and a low emissions scenario that assumes aggressive reductions worldwide (B1 in brown).

Impacts on Transportation

• Sea level rise and storm surge will increase the risk of major coastal impacts, including both temporary and permanent flooding of airports, roads, rail lines, and tunnels.
• Flooding from increasingly intense downpours will increase the risk of disruptions and delays in air, rail, and road transportation, and damage from mudslides in some areas.
• The increase in extreme heat will limit some transportation operations and cause pavement and track damage. Decreased extreme cold will provide some benefits such as reduced snow and ice removal costs.
• Increased intensity of strong hurricanes would lead to more evacuations, infrastructure damage and failure, and transportation interruptions.
• Arctic warming will continue to reduce sea ice, lengthening the ocean transport season, but also resulting in greater coastal erosion due to waves. This will affect coastal villages in Alaska and Canada.
• Permafrost thaw in Alaska will damage infrastructure. The ice road season, vital to many villages for getting food and supplies, will become shorter and more dangerous.

Impacts on Energy Supply and Use

• Warming will be accompanied by decreases in demand for heating energy and increases in demand for cooling energy. The latter will result in significant increases in electricity use and higher peak demand in most regions.
• Energy production is likely to be constrained by rising temperatures and limited water supplies in many regions.
• Energy production and delivery systems are exposed to sea level rise and extreme weather events in vulnerable regions.
• Climate change is likely to affect some renewable energy sources across the nation, such as hydropower production in regions subject to changing patterns of precipitation or snowmelt.

Changes in residential energy demand, from heating to cooling of homes in the U.S., from 1970-1010. From the National Climate Assessment 2014.

Impacts on Water Resources

• Climate change has already altered, and will continue to alter, the water cycle, affecting where, when, and how much water is available for all uses.
• Floods and droughts are likely to become more common and more intense as regional and seasonal precipitation patterns change, and rainfall becomes more concentrated into heavy events (with longer, hotter dry periods in between).
• Precipitation and runoff are likely to increase in the Northeast, Northwest, and Midwest in winter and spring, and decrease in the South, especially the Southwest, in spring and summer.
• In areas where snowpack dominates, the timing of runoff will continue to shift to earlier in the spring and flows will be lower in late summer. Spring flooding will become more common in the near future.
• Surface water quality and groundwater quantity will be negatively affected by a changing climate, as waters warm, causing algal blooms, and contamination increases with larger storms.
• Climate change will place additional burdens on already stressed water systems.
• The past century is no longer a reasonable guide to the future for water management. Water managers need to assess future supply specific to their region.
• The past century is no longer a reasonable guide to the future for water management.