Climate Change Indicators in the US.

Multiple lines of evidence reveal the far-reaching impacts of climate change on the people and environment of the United States. Tracking observations over time reveals valuable data about what people are experiencing today. These data can help guide climate actions that are effective, are equitable, and will address challenges into the future. Understanding and addressing climate change is critical to the Environmental Protection Agency’s (EPA’s) mission of protecting human health and the environment.

What is climate change?

“Climate change” refers to any substantial change in measures of climate (such as temperature or precipitation) lasting for decades or longer. Natural factors have caused the climate to change during previous periods of the Earth’s history, but human activities are the main cause of the changes that are being observed now.

What is a climate change indicator?

One important way to track and communicate the causes and effects of climate change is through indicators. An indicator represents the state or trend of certain environmental or societal conditions in a given place and time period. EPA’s indicators are designed to help readers understand observed long-term trends related to the causes and effects of climate change. In other words, they provide important evidence of how our climate is changing all around us.

The Indicators

Greenhouse Gases.

As greenhouse gas emissions from human activities increase, they build up in the atmosphere and warm the climate, leading to many other changes around the world—in the atmosphere, on land, and in the oceans. The indicators presented in other chapters of this report and on EPA’s website illustrate many of these changes and their effects on people, society, and the environment.

Heat on the Rise.

As the concentrations of heat-trapping greenhouse gases in the atmosphere continue to increase, the United States has experienced warming temperatures, more unusually hot summer days, and more frequent heat waves that threaten people’s health and strain the electric power grid.

Extreme Events.

Rising global average temperature is associated with widespread changes in weather patterns. Extreme events such as heavy rainstorms, hurricanes, floods, droughts, and wildfires have happened throughout history, but human-induced climate change is expected to make these events more frequent and/or intense. While risks vary across the country, these events are among the nation’s costliest disasters, sometimes causing great damage to ecosystems, communities, and the economy.

Water Resources at Risk.

Clean fresh water is essential to life on the Earth, and climate change is affecting the planet’s water resources. As the climate warms, changing precipitation patterns, drought, decreasing amounts of snow, and earlier snowmelt all pose risks to water supplies in the United States, affecting communities, livelihoods, and ecosystems.

Changing Seasons.

Although the timing, duration, and intensity of the seasons vary naturally from year to year, climate change is driving longer-term changes in seasonality and fundamentally altering the ways in which humans and natural systems experience and interact with seasonal events. These changes lead to wide-ranging impacts such as warmer winters, lakes thawing earlier, longer growing seasons, and worsening allergies for people.

Ocean Impacts.

The heat-trapping greenhouse gases that humans have added to the atmosphere are making the Earth’s oceans warmer and more acidic. Changes in the oceans affect the Earth’s climate and weather patterns and threaten marine ecosystems and biodiversity and the people whose livelihoods depend on them.

Rising Seas.

As the temperature of the Earth changes, so does sea level throughout the world’s oceans. Water from melting ice sheets and glaciers on land ultimately flows into the ocean. Also, as water in the ocean warms, it expands slightly, increasing the volume of water in the ocean. Both of these factors contribute to sea level rise, which increases coastal flooding and other coastal risks.

Alaska’s Warming Climate.

The Arctic is warming more quickly than the rest of the world, as is Alaska—the northernmost U.S. state. Alaska is also uniquely vulnerable to climate change due to its frozen features. Alaska is the only state with widespread permafrost (underlying 80 percent of its land) and significant sea ice extent, which are an integral part of life. Entire ecosystems, communities, and Indigenous ways of life could vanish as these frozen features shrink or disappear.