Frequent Questions

EPA partners with more than 50 data contributors from various government agencies, academic institutions, and other U.S and international organizations to compile a key set of indicators related to the causes and effects of climate change. Explore the questions and answers below to learn more about the indicators.

• What is an indicator?
• Why does EPA compile and publish climate change indicators?
• How do the indicators relate to climate change?
• Where do the indicator data come from?
• What geographic areas and time periods do the indicators cover?
• Why do some indicator trends fluctuate over time?
• Which greenhouse gases do these indicators track?
• How do indicators relate to human health? 
• How do I use this resource?
• How do I cite this resource?
• Where can I find downloads of past indicator reports and related content?
• How do EPA's climate indicators relate to the USGCRP, the National Climate Assessment, and other federal climate indicator efforts?

What is an indicator?

One important way to track and communicate the causes and effects of climate change is through the use of indicators. An indicator represents the state or trend of certain environmental or societal conditions over a given area and a specified period of time. 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 "what climate change looks like." For example, long-term measurements of temperature in the United States and globally are used as an indicator to track and better understand the effects of changes in the Earth's climate.

Why does EPA compile and publish climate change indicators?

EPA compiles these indicators with the primary goal of informing our understanding of climate change. They are designed so that the public, scientists, analysts, decision-makers, educators, and others can use climate change indicators as a basis for:

• Effectively communicating relevant climate science information in a sound, transparent, and easy-to-understand way.
• Assessing trends in environmental quality, factors that influence the environment, and effects on ecosystems and society.
• Informing science-based decision-making.

EPA publishes these indicators to make them accessible and available to use in a variety of ways. These indicators characterize observed changes from long-term records related to the causes and effects of climate change; the significance of these changes; and their possible consequences for people, the environment, and society. The indicators presented here do not cover all possible measures of the causes and effects of climate change, nor do they capture all possible climate change indicators found in the full body of scientific assessment literature. Instead, these indicators represent a wide-ranging set of high-quality, long-term data that show observed changes in the Earth’s climate system and several climate-relevant impacts. Together, these indicators present compelling evidence that climate change is happening now in the United States and globally.

How do the indicators relate to climate change?

All of the indicators on this website relate to either the causes or the effects of climate change. Some indicators show trends that can be more directly linked to human-induced climate change than others. Collectively, the trends depicted in these indicators provide important evidence of "what climate change looks like."

Although each indicator has a connection to climate change, EPA's indicators do not attempt to identify either the extent to which a certain indicator is driving climate change, or the relative role of climate change in causing a trend in an observed indicator. Connections between human activities, climate change, and observed indicators are explored in more detail elsewhere in the scientific literature. For example, see the U.S. Global Change Research Program's National Climate Assessment.

Some indicators are directly linked to human activities that cause climate change, such as Global Greenhouse Gas Emissions. Changes depicted by other indicators, like U.S. and Global Temperature, have been confidently linked with the increase in greenhouse gases caused by human activity. Some of the trends in other indicators, such as Wildfires, are consistent with what one would expect in a warming climate but may also be influenced by limitations in the historical data or other factors in addition to climate change. A few indicators, like West Nile Virus, though known to be influenced by climate change, do not yet show any significant trend. In some cases, this could be because the period for which data are available or the geographic scale in which they are presented is limited.

Where do the indicator data come from?

EPA partners with more than 50 data contributors from various U.S. and international government agencies, academic institutions, and other organizations to compile and communicate key indicators related to the causes and effects of climate change. EPA's indicators consist of peer-reviewed, publicly available data. In addition to being published on EPA's website, these data sets have been published in the scientific literature and in government and academic reports. Details on each underlying data set as well as where to find it are provided in the technical documentation on each indicator's webpage.

What geographic areas and time periods do the indicators cover?

Trends relevant to climate change are best viewed at broad geographic scales and over long time periods. EPA's indicators are based on historical records that go back in time as far as possible without sacrificing data quality, so each indicator's time scale varies.

Most of EPA's indicators focus on the United States. However, some include global trends to provide context or a basis for comparison, or because they are intrinsically global in nature, such as Atmospheric Concentrations of Greenhouse Gases. EPA attempts to present multiple scales (national, regional, or location-specific) in cases where the underlying data allow such scaling. The geographic extent and timeframe of each indicator largely depend on data availability and the nature of what is being measured.

EPA also includes features such as “Community Connection” and “A Closer Look” (e.g., Cherry Blossom Bloom Dates in Washington, D.C.) that focus on a particular region or localized area of interest to engage readers in particular areas or topics of interest within the United States. While the features and their underlying data are not national in scale or representative of broad geographic areas, these features are screened, developed, and documented in a manner consistent with other indicators.

Why do some indicator trends fluctuate over time?

Although the climate is continually changing, not every climate change indicator shows a pattern of steady change over the period of record. The Earth is a complex system, and there are always natural variations from one year to the next—for example, a very warm year followed by a colder year. The Earth’s climate also goes through other natural cycles that play out over a period of several years or even decades. Individual years or even individual decades can deviate from the long-term trend. Human factors may also influence a trend—for example, human activities and land management practices can affect wildfire activity from year to year.

Which greenhouse gases do these indicators track?

EPA’s greenhouse-gas-related indicators focus on most of the major, well-mixed greenhouse gases that contribute to the vast majority of warming of the climate when they are emitted into the atmosphere. These major gases are carbon dioxide, methane, nitrous oxide, and fluorinated gases. Some of these gases are produced almost entirely by human activities, while others come from a combination of natural sources and human activities.

Many of these major greenhouse gases remain in the atmosphere for tens to thousands of years after being released. They become globally mixed in the lower part of the atmosphere, called the troposphere (the first several miles above the Earth’s surface), reflecting the combined emissions worldwide from the past and present. Due to this global mixing, concentrations of these gases are fairly similar no matter where in the world they are measured.

Other substances that have much shorter atmospheric lifetimes (i.e., less than a year) are still relevant to climate change. Important short-lived substances that affect the climate include water vapor, ozone in the troposphere, pollutants that lead to ozone formation, and aerosols (atmospheric particles) such as black carbon and sulfates. Water vapor, tropospheric ozone, and black carbon contribute to warming, while other aerosols produce a cooling effect. In addition to several long-lived greenhouse gases, EPA's Atmospheric Concentrations of Greenhouse Gases indicator tracks concentrations of ozone in the layers of the Earth's atmosphere, while Figure 2 of the Climate Forcing indicator shows the influence of a variety of short-lived substances.

How do indicators relate to human health?

Indicators provide key information on changes that are occurring in our environment, like increasing temperatures or more severe extreme weather events, which can threaten people's health. Tracking changes in climate impacts and exposures improves understanding of changes in health risk, even if the actual health outcome is difficult to quantify. For example, while only some indicators exist for human health outcomes related to climate change, like West Nile Virus, Lyme Disease, Heat-Related Deaths, and Cold-Related Deaths, other indicators—like Ragweed Pollen Season, Heat Waves, or Wildfires—give insight into the changing risks to human health. There are many factors other than climate that affect human health; these are discussed in more detail in EPA's overview of the connections between climate change and human health.

How do I use this resource? 

EPA's climate change indicators are grouped into six categories:

• Greenhouse Gases
• Weather and Climate
• Oceans
• Snow and Ice
• Health and Society
• Ecosystems

Each indicator can be accessed through the links above or directly from the View the Indicators page. Within each indicator, you will see:

• Figures: One or more figures depicting changes over time, displayed as a graph or map. Some indicators include interactive graphs, maps, and images. Beneath each figure, readers will find an explanatory caption, a data source citation, the date when the most recent data update was published on EPA’s website, and one or more of the following buttons:
  •   A downloadable .csv file, which can be opened in programs such as Excel. This file provides all the numbers depicted in the graphic.
  •   A downloadable high-resolution version of the figure, including the title and a full data source citation. This version may be helpful for those who wish to share or reuse a figure (see recommended citation).
  •   A link to an interactive map with clickable features.
• Key points: Key points about what the indicator shows.
• Background: Background on how the indicator relates to climate change.
• About the indicator: A description of the how the indicator was developed.
• About the data: Information about the data used to produce the indicator, including data sources and notes about factors that may influence how one interprets the data.
• Technical documentation: A link to comprehensive documentation (PDF) that describes the data sources and analytical methods for the indicator.

How do I cite this resource?

EPA recommends the following citation for this resource and for individual indicators:

U.S. Environmental Protection Agency. Climate Change Indicators in the United States. Accessed [Month Year]. www.epa.gov/climate-indicators.

U.S. Environmental Protection Agency. Climate Change Indicators in the United States. [Name of Indicator]. Accessed [Month Year]. [URL of Indicator].

Where can I find downloads of past indicator reports and content?

Visit EPA's publications page for PDF versions of previous indicator reports, along with related fact sheets and brochures. EPA has published several summary reports of Climate Change Indicators in the United States, starting in 2010, then in 2012, 2014, 2016, and most recently, 2024.

The online resource is updated periodically as new data become available, and thus may differ from the most recent reports and content.

How do EPA's climate indicators relate to the USGCRP, the National Climate Assessment, and other federal indicator efforts?

EPA's indicators are an example of a well-established, nationally relevant set of indicators representative of data from several of the federal agencies participating in the U.S. Global Change Research Program (USGCRP). EPA works closely with several of these agencies (e.g., Centers for Disease Control and Prevention, National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, U.S. Geological Survey, and U.S. Department of Agriculture) and serves as a co-chair of USGCRP’s Interagency Indicators Workgroup. EPA’s climate indicators are leveraged as scientific input to the federal interagency effort. EPA will continue to work in partnership with coordinating bodies such as the USGCRP and with other agencies, organizations, and individuals to collect and communicate useful data and to inform policies and programs based on this knowledge. For example, EPA collaborated with the U.S. Forest Service to develop a StoryMap showing indicators that help the user explore the causes and effects of climate change.