The link between climate change and extreme weather
What is extreme weather?

Extreme weather and climate events are events that:
  • typically don't happen very frequently, such as droughts or floods that have historically occurred on average only once in 100 years.
  • vary from "the norm" in severity or duration, like heat waves.
  • have severe impacts, like hurricanes.
Scientists study many aspects of change in extreme weather and climate events. These include:
  • Frequency: Are events occurring more often than they did in the past?
  • Intensity: Are events getting more severe, with the potential for more damaging effects?
  • Duration: Are events lasting longer than "the norm"?
  • Timing: Are events occurring earlier or later in the season or the year than they used to?
Extreme weather is typically rare. But climate change is increasing the odds of more extreme weather events taking place.
Extreme Weather

Establishing the most likely causes behind an extreme weather event can be challenging, since these events are due to combinations of multiple factors, including natural variability.

Nevertheless, scientists have been able to draw a connection between some types of extreme climate patterns—an even some individual events—and climate change. A good way to think about this connection is to focus on whether an extreme weather event was made more likely by climate change.

There have been changes in some types of extreme weather events in the United States over the last several decades, including more intense and frequent heat waves, less frequent and intense cold waves, and regional changes in floods, droughts, and wildfires. This rise in extreme weather events fits a pattern you can expect with a warming planet. Scientists project that climate change will make some of these extreme weather events more likely to occur and/or more likely to be severe.
Trends in Specific Extreme Weather Events - Heat Waves
  • Why does it matter? Heat waves can have serious health consequences, particularly for older adults, young children, the poor, and people with certain pre-existing health conditions, like asthma or heart disease. Excessive heat can also kill or injure crops and livestock, and it can lead to power outages as heavy demand for air conditioning strains the power grid.
  • How does it relate to climate change? Even a small rise in average temperature brought on by climate change can boost the odds of extreme heat and heat waves.
  • What's happening? Climate change has increased the likelihood of more frequent and more severe heat waves. Heat waves have generally become more frequent and intense across the United States in recent decades, particularly in the western United States (including Alaska). The impacts of heat waves are greatest in the Northeast and Midwest, and in urban areas, where the urban heat island effect increases vulnerability to heat-related health impacts.
  • What's ahead? Heat waves are expected to become more frequent, longer, and more intense in the years ahead. The number of extremely hot days is projected increase throughout the United States.
  • How sure is the science? Scientists are highly confident that heat waves and other extreme heat events have and will continue to become more frequent and intense due to climate change.
Adaptation: Reducing the Threat of Climate Change and Preparing for Impacts

Extreme weather and climate events pose a serious threat to the health and welfare of American families and businesses.

Picture - This map summarizes the number of times each state has been affected by weather and climate events over the past 30 years that have resulted in more than a billion dollars in damages. The Southeast has been affected by more billion-dollar disasters than any other region. The primary disaster type for coastal states such as Florida is hurricanes, while interior and northern states in the region also experience sizeable numbers of tornadoes and winter storms.

For instance, between 2011 and 2013, the United States experienced 32 weather events that each caused at least one billion dollars in damages. 2012 ranks as 2nd costliest year on record, with more than $110 billion in damages.

EPA is taking a number of common-sense actions to reduce greenhouse gas emissions and help cities and towns build more resilient communities to prepare for the impacts of a changing climate, including the weather extremes described above.
Key Points
  • Extreme weather events are becoming more frequent and/or severe around the world. This is consistent with what we expect with a warming planet.
  • Increasingly frequent and/or severe weather events have serious consequences for society and ecosystems.
  • Between 2011 and 2013, the United States experienced 32 weather events that each caused at least one billion dollars in damages.
  • Changes in some weather events are more closely linked to climate change than others.
  • Understanding the links between climate change and extreme events can help us plan for the future.
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