Climate change is projected to produce more intense and frequent extreme weather events, multiple weather disturbances, along with broader climatological effects, such as sea level rise. These are almost certain to have significant direct and indirect social, economic, political, and security implications during the next 20 years. These effects will be especially pronounced as populations continue to concentrate in climate-vulnerable locales such as coastal areas, water-stressed regions, and ever-growing cities. These effects are likely to pose significant national security challenges for the United States over the next two decades, though models forecast the most dramatic effects further into the future. While specific extreme weather events remain difficult to attribute entirely to climate change, unusual patterns of extreme and record-breaking weather events are likely to become more common, according to the Intergovernmental Panel on Climate Change (IPCC).
- Extreme weather events, such as heavy rainfalls, floods, droughts, cyclones, and heatwaves, will disrupt critical human and natural systems. They could trigger crop failures, wildfires, energy blackouts, infrastructure breakdown, or infectious disease outbreaks. The frequency and magnitude of such events are increasing as the climate changes, according to the IPCC.
- Moreover, multiple weather disturbances—when several extreme weather events occur within a small region or short time—compound their impact while undercutting efforts by people and governments to cope. Clusters or rapid sequences of relatively modest weather events may cause more damage than very powerful single events.
- Global climatological stresses—such as sea-level rise, ocean acidification, permafrost and glacial melt, air quality degradation, changes in cloud cover, and sustained shifts in temperature and precipitation—could substantially alter broader natural and manmade systems involving where and how humans live and patterns of infectious disease outbreaks, as well as critical ecosystems.
The following table lays out the IPCC baseline for likely increases in extreme weather events in the decades ahead. Such events may occur at different rates of frequency, intensity, and location compared to historical patterns, and lack of preparedness for those changes—such as weather-related disasters, drought, famine, supply chain breakdown, or damage to infrastructure—may prove a primary cause of disruption.
According to the National Oceanic and Atmospheric Administration, weather reflects short-term conditions of the atmosphere in a particular region while climate encompasses the averages, variability, and other statistics of weather over longer periods of time. Weather includes very hot or cold or rainy days, while extreme weather events include extended droughts, floods, heatwaves, coldwaves, and intense tropical storms. Climate change reflects nonrandom change in climate measured over several decades or longer. Climate variability reflects the way that climate fluctuates above or below long term average values.
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