Understanding Climate Change
With congressional and public interest in climate change growing over the past 20 years, science policy and data on greenhouse gas emissions have emerged as particularly important issues to help inform climate policy.
Certain gases, such as carbon dioxide, methane
Understanding Climate Change
With congressional and public interest in climate change growing over the past 20 years, science policy and data on greenhouse gas emissions have emerged as particularly important issues to help inform climate policy.
Certain gases, such as carbon dioxide, methane, and nitrous oxide, trap energy from the sun that would otherwise escape Earth's atmosphere. High concentrations of these gases create a greenhouse effect that raises average global temperatures. Global temperature increases may contribute to a gradual change in the balance of energy flowing into and away from Earth's surface. Earth's climate system is driven by energy from the sun and is maintained by complex interactions among the atmosphere, the oceans, and the reflectivity of Earth’s surface, among other factors. Earth's system maintains a constant average temperature only if the same amount of energy leaves the system as enters it. If more energy enters than leaves, the difference manifests as a temperature increase. The interactive feature (figure 1) shows current estimates of the equilibrium transfer of energy.
Global Average Energy Budget of the Earth's Atmosphere
Carbon dioxide is the key greenhouse gas affected by human activity, accounting for about 84% of U.S. emissions in 2011. The next interactive feature (figure 2) illustrates Earth’s carbon cycle, which regulates the flow of carbon between the atmosphere and land-based and oceanic sinks.
Depiction of the Global Carbon Cycle Changes Over Time
Since the 1700s, atmospheric carbon dioxide concentrations have risen from approximately 280 parts per million to approximately 400 parts per million (figure 3). According to the May 2014 National Climate Assessment, after decades of increases, carbon dioxideemissions from energy use (which account for 97% of total U.S. emissions) decline