Climate Change

Climate change is quickly becoming the biggest threat to the long-term survival of America’s wildlife. No longer is climate change something only facing future generations—changes to our climate are being documented all across the planet today, and people, animals, and plants are already feeling the heat. This warming signal is also found in ocean temperatures, soil temperatures, melting glaciers, and melting polar ice caps. It has been linked to widespread impacts on ecosystems around the planet. This preponderance of evidence all points to the conclusion that our planet is warming, and natural systems are struggling to keep up.

What's Happening?

Temperatures are increasing: The most striking evidence of a climate change trend is closely scrutinized data that show a relatively rapid and widespread increase in temperature during the past century. Average temperatures in the United States over the last century have already increased by more than one degree Fahrenheit, and the Earth's atmosphere has warmed by 1.5 degrees Fahrenheit since 1900. The 10 warmest years on record have all occurred since 1998, with 2016 being the warmest year on record. The rising temperatures observed since 1978 are particularly noteworthy because the rate of increase is so high and because, during the same period, the energy reaching the Earth from the Sun had been measured precisely enough to conclude that Earth's warming was not due to changes in the Sun.

Sea levels are rising: Global sea level has increased by roughly eight inches over the past century, and the rate of increase is accelerating. Climate change causes sea level rise in two ways: ocean water is expanding as it warms, and land-based ice in glaciers and ice sheets is melting. Sea level rise has been happening even faster than scientists anticipated a few years ago. If recent projections are accurate, 2 to 3 degrees Fahrenheit warming could bring about three feet of global sea level rise by 2100, displacing approximately 56 million people in 84 developing countries around the world. Coastal habitats also face major changes as low-lying areas are inundated with saltwater.

Sea ice is melting: Declining sea ice is one of the most visible signs of climate change on our planet. Since 1979, Arctic sea ice extent in September (when the annual minimum is reached) has declined by more than 30 percent, according to the National Snow and Ice Data Center. The ice extent has been declining in other seasons too. Despite slightly larger ice extents in 2009, recent observations indicated the ice is thinner and much younger (less multi-year ice) than it used to be. Covering an average of 9.6 million square miles, these areas of ice floating on ocean waters play an important role in regulating our climate, by reflecting some sunlight back to space, and in the life cycles of many polar species, such as polar bears, seals, and walruses.

Precipitation patterns are changing: Some places are getting more rainfall and others are getting less. Nearly everywhere is experiencing more heavy rainfall events, as warmer air is able to hold more water vapor. Right here in the United States, we are already seeing some important trends in precipitation. The Southwest appears to be shifting to a more arid climate, in which Dust Bowl conditions will become the new norm. Annual precipitation totals in the Northeast, Midwest, and Plains have increased by 5 to 20 percent during the last 50 years. The southeastern United States is having both more drought and more floods. Read more about how climate change is causing extreme weather.

Oceans are acidifying: The ocean has absorbed a large fraction of the carbon dioxide that fossil fuel burning has pumped into the atmosphere, slowing the rate of climate change. But all this extra carbon dioxide is impacting the ocean, too. The pH of surface seawater has decreased by 0.1 units since 1750 and is projected to drop another 0.5 units by 2100 if no action is taken to curb fossil fuel emissions. These changes would take tens of thousands of years to reverse.

Human Impact

Climate change is caused by humans. Scientists have concluded that most of the observed warming is very likely due to the burning of coal, oil, and gas. This conclusion is based on a detailed understanding of the atmospheric greenhouse effect and how human activities have been changing it. At the same time, other reasonable explanations, most notably changes in the sun, have been ruled out.

The atmospheric greenhouse effect naturally keeps our planet warm enough to be livable. Sunlight passes through the atmosphere. Light-colored surfaces, such as clouds or ice caps, radiate some heat back into space. But most of the incoming heat warms the planet's surface. The earth then radiates some heat back into the atmosphere. Some of that heat is trapped by greenhouse gases in the atmosphere, including carbon dioxide.

Human activity—such as burning fossil fuels—causes more greenhouse gases to build up in the atmosphere. As the atmosphere "thickens" with more greenhouse gases, more heat is held in. Fossil fuels such as oil, coal and natural gas are high in carbon and, when burned, produce major amounts of carbon dioxide. A single gallon of gasoline, when burned, puts 19 pounds of carbon dioxide into the atmosphere.

The role of atmospheric carbon dioxide in warming the Earth's surface was first demonstrated by Swedish scientist Svante Arrhenius more than 100 years ago. Scientific data have since established that, for hundreds of thousands of years, changes in temperature have closely tracked with atmospheric carbon dioxide concentrations. Since the Industrial Revolution, the burning of coal, oil and natural gas has emitted roughly 500 billion tons of carbon dioxide, about half of which remains in the atmosphere. This carbon dioxide is the biggest factor responsible for recent warming trends.

Additional Threats to Wildlife

Loss of wetlands: Higher temperatures will lead to drier conditions in the Midwest’s Prairie Pothole region, one of the most important breeding areas for North American waterfowl.

Sea level rise: Sea-level rise will inundate beaches and marshes and cause erosion on both coasts, diminishing habitat for birds, invertebrates, fish, and other coastal wildlife.

Invasive species and disease: Higher average temperatures and changes in rain and snow patterns will enable some invasive plant species to move into new areas. Insect pest infestations will be more severe as pests such as mountain pine beetle are able to take advantage of drought-weakened plants. Pathogens and their hosts that thrive in higher temperatures will spread to new areas.

Sources
Observed Impacts of Climate Change in the United States, Pew Center on Global Climate Change
National Aeronautics and Space Administration (NASA)
National Oceanic and Atmospheric Administration (NOAA)

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