This website is the digital version of the 2014 National Climate Assessment, produced in collaboration with the U.S. Global Change Research Program.

For the official version, please refer to the PDF in the downloads section. The downloadable PDF is the official version of the 2014 National Climate Assessment.

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Welcome to the National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

Explore the effects of climate change
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Widespread Impacts

Impacts related to climate change are already evident in many sectors and are expected to become increasingly disruptive across the nation throughout this century and beyond.

Explore widespread impacts.



Climate change is already affecting societies and the natural world. Climate change interacts with other environmental and societal factors in ways that can either moderate or intensify these impacts. The types and magnitudes of impacts vary across the nation and through time. Children, the elderly, the sick, and the poor are especially vulnerable. There is mounting evidence that harm to the nation will increase substantially in the future unless global emissions of heat-trapping gases are greatly reduced.

Widespread Impacts

coastal flooding

Storm surge on top of sea level rise exacerbates coastal flooding during hurricanes.

Because environmental, cultural, and socioeconomic systems are tightly coupled, climate change impacts can either be amplified or reduced by cultural and socioeconomic decisions. In many arenas, it is clear that societal decisions have substantial influence on the vulnerability of valued resources to climate change. For example, rapid population growth and development in coastal areas tends to amplify climate change related impacts. Recognition of these couplings, together with recognition of multiple sources of vulnerability, helps identify what information decision-makers need as they manage risks.

Multiple System Failures During Extreme Events

Katrina Diaspora Katrina Diaspora Details/Download

Impacts are particularly severe when critical systems simultaneously fail. We have already seen multiple system failures during an extreme weather event in the United States, as when Hurricane Katrina struck New Orleans.2 Infrastructure and evacuation failures and collapse of critical response services during a storm is one example of multiple system failures. Another example is a loss of electrical power during heat waves or wildfires, which can reduce food and water safety.3 Air conditioning has helped reduce illness and death due to extreme heat,4 but if power is lost, everyone is vulnerable. By their nature, such events can exceed our capacity to respond.5 In succession, these events severely deplete resources needed to respond, from the individual to the national scale, but disproportionately affect the most vulnerable populations.6

Coral Reef Ecosystem Collapse

In many social and natural systems, climate change combines with other stresses to cause or expand impacts. For example, coral reefs are threatened by a combination of ocean acidification caused by increased carbon dioxide, rising ocean temperatures, and a variety of other factors caused by human activities.

Coral Bleaching

Warming Seas Are a Double-blow to Corals

Drag the slider to view time series effect

Warm water caused this coral colony to “bleach” as it expelled the symbiotic algae that gave it color and nourishment. The coral then experienced more disease, which eventually killed the colony.


Recent research indicates that 75% of the world’s coral reefs are threatened due to the interactive effects of climate change and local sources of stress, such as overfishing, nutrient pollution, and disease.7,8,9,10,11 In Florida, all reefs are rated as threatened; with significant impacts on valuable ecosystem services they provide.12 Caribbean coral cover has decreased 80% in less than three decades.13 These declines have in turn led to a flattening of the three dimensional structure of coral reefs and hence a decrease in the capacity of coral reefs to provide shelter and additional resources for other reef-dependent ocean life.14

The relationship between coral and zooxanthellae (algae vital for reef-building corals) is disrupted by higher than usual temperatures and results in a condition where the coral is still alive, but devoid of all its color (bleaching). Bleached corals can later die or become infected with disease.15,16 Thus, high temperature events alone can kill large stretches of coral reef, although cold water and poor water quality can also cause localized bleaching and death. Evidence suggests that relatively pristine reefs, with fewer human impacts and with intact fish and associated invertebrate communities, are more resilient to coral bleaching and disease.17

Cascading Effects Across Sectors

Agriculture, water, energy, transportation, and more, are all affected by climate change. These sectors of our economy do not exist in isolation and are linked in increasingly complex ways. For example, water supply and energy use are completely intertwined, since water is used to generate energy, and energy is required to pump, treat, and deliver water – which means that irrigation-dependent farmers and urban dwellers are linked as well.

farmer examines parched land

Heat and drought lead to cascading impacts among sectors including agriculture, water, and energy.

A recent illustration of these interconnections took place during the widespread drought of 2011-2012 when high temperatures caused increased demand for electricity for air conditioning, which resulted in increased water withdrawal and consumption for electricity generation. Heat, increased evaporation, drier soils, and lack of rain led to higher irrigation demands, which added stress on water resources required for energy production. At the same time, low-flowing and warmer rivers threatened to suspend power plant production in several locations, reducing the options for dealing with the concurrent increase in electricity demand.

With electricity demands at all-time highs, water shortages threatened more than 3,000 megawatts of generating capacity – enough power to supply more than one million homes.18 As a result of the record demand and reduced supply, electricity prices spiked.19


  1. Alvarez-Filip, L., N. K. Dulvy, J. A. Gill, I. M. Côté, and A. R. Watkinson, 2009: Flattening of Caribbean coral reefs: Region-wide declines in architectural complexity. Proceedings of the Royal Society B: Biological Sciences, 276, 3019-3025, doi:10.1098/rspb.2009.0339. URL | Detail

  2. Anderson, G. B., and M. L. Bell, 2012: Lights out: Impact of the August 2003 power outage on mortality in New York, NY. Epidemiology, 23, 189-193, doi:10.1097/EDE.0b013e318245c61c. | Detail

  3. Burke, L., L. Reytar, M. Spalding, and A. Perry, 2011: Reefs at Risk Revisited. World Resources Institute, 130 pp. URL | Detail

  4. Dudgeon, S. R., R. B. Aronson, J. F. Bruno, and W. F. Precht, 2010: Phase shifts and stable states on coral reefs. Marine Ecology Progress Series, 413, 201-216, doi:10.3354/meps08751. URL | Detail

  5. ERCOT, 2011: Grid Operations and Planning Report (Austin, Texas, December 12-13, 2011). 25 pp., Electric Reliability Council of Texas. URL | Detail

  6. Frieler, K., M. Meinshausen, A. Golly, M. Mengel, K. Lebek, S. D. Donner, and O. Hoegh-Guldberg, 2013: Limiting global warming to 2°C is unlikely to save most coral reefs. Nature Climate Change, 3, 165-170, doi:10.1038/nclimate1674. | Detail

  7. Gardner, T. A., I. M. Côté, J. A. Gill, A. Grant, and A. R. Watkinson, 2003: Long-term region-wide declines in Caribbean corals. Science, 301, 958-960, doi:10.1126/science.1086050. | Detail

  8. Giberson, M., 2011: Power Consumption Reaches New Peaks in Texas, ERCOT Narrowly Avoids Rolling Blackouts. The Energy Collective. URL | Detail

  9. Hess, J. J., J. Z. McDowell, and G. Luber, 2012: Integrating climate change adaptation into public health practice: Using adaptive management to increase adaptive capacity and build resilience. Environmental Health Perspectives, 120, 171-179, doi:10.1289/ehp.1103515. URL | Detail

  10. Hoegh-Guldberg, O., P. J. Mumby, A. J. Hooten, R. S. Steneck, P. Greenfield, E. Gomez, C. D. Harvell, P. F. Sale, A. J. Edwards, K. Caldeira, N. Knowlton, C. M. Eakin, R. Iglesias-Prieto, N. Muthiga, R. H. Bradbury, A. Dubi, and M. E. Hatziolos, 2007: Coral reefs under rapid climate change and ocean acidification. Science, 318, 1737-1742, doi:10.1126/science.1152509. | Detail

  11. Hughes, T. P., N. A. J. Graham, J. B. C. Jackson, P. J. Mumby, and R. S. Steneck, 2010: Rising to the challenge of sustaining coral reef resilience. Trends in Ecology & Evolution, 25, 633-642, doi:10.1016/j.tree.2010.07.011. | Detail

  12. Kent, J. D., 2006: Louisiana Hurricane Impact Atlas. 39 pp., Louisiana Geographic Information Center, Baton Rouge, LA. URL | Detail

  13. Lister, S. A., 2005: Hurricane Katrina: The Public Health and Medical Response. 24 pp., Congressional Research Service Report for Congress. URL | Detail

  14. Miller, J., E. Muller, C. Rogers, R. Waara, A. Atkinson, K. R. T. Whelan, M. Patterson, and B. Witcher, 2009: Coral disease following massive bleaching in 2005 causes 60% decline in coral cover on reefs in the US Virgin Islands. Coral Reefs, 28, 925-937, doi:10.1007/s00338-009-0531-7. URL | Detail

  15. Mumby, P. J., and R. S. Steneck, 2011: The resilience of coral reefs and its implications for reef management. Coral Reefs: An Ecosystem in Transition, Z. Dubinsky and N. Stambler, Eds., 509-519. | Detail

  16. Ostro, B., S. Rauch, R. Green, B. Malig, and R. Basu, 2010: The effects of temperature and use of air conditioning on hospitalizations. American Journal of Epidemiology, 172, 1053-1061, doi:10.1093/aje/kwq231. URL | Detail

  17. Sandin, S. A., J. E. Smith, E. E. DeMartini, E. A. Dinsdale, S. D. Donner, A. M. Friedlander, T. Konotchick, M. Malay, J. E. Maragos, D. Obura, O. Pantos, G. Paulay, M. Richie, F. Rohwer, R. E. Schroeder, S. Walsh, J. B. C. Jackson, N. Knowlton, and E. Sala, 2008: Baselines and degradation of coral reefs in the northern Line Islands. PLoS ONE, 3, 1-11, doi:10.1371/journal.pone.0001548. URL | Detail

  18. Shonkoff, S. B., R. Morello-Frosch, M. Pastor, and J. Sadd, 2011: The climate gap: Environmental health and equity implications of climate change and mitigation policies in California—a review of the literature. Climatic Change, 485-503, doi:10.1007/s10584-011-0310-7. | Detail

  19. Weil, E., A. Croquer, and I. Urreiztieta, 2009: Temporal variability and impact of coral diseases and bleaching in La Parguera, Puerto Rico from 2003–2007. Caribbean Journal of Science, 45, 221-246. URL | Detail

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

United States Global Change Research Program logo United States Global Change Research Program participating agency logos