Human activity is warming the planet. How much it will warm by the end of this century depends on our choices now.

Without more progress in curbing emissions, average temperatures could rise between 4.7°F to 8.6°F (2.6°C to 4.8°C) by the end of the century, compared to the average temperature around the end of the 20th century (1986-2005).

Human, plants, and animals are already feeling the impacts, which will grow over time. Warmer air and water temperatures are causing sea level to rise and extreme weather events to be more frequent and intense. Rising carbon dioxide concentrations are making the oceans more acidic.

Climate impacts are not evenly distributed, either globally or in the United States. Researchers estimate that each degree of warming causes about a 1 percent drop in U.S. GDP. But some regions will experience much larger economic losses. Parts of Florida and the Gulf Coast could see their economies shrink 25 percent if global emissions go unchecked and if local adaptation actions are not implemented.

Although reducing emissions now can avoid the worst consequences, some impacts are unavoidable. The changes we are experiencing today will continue to grow.

Sea-Level Rise

Warming increases sea levels directly (water expands when it warms) and indirectly (by melting glaciers and polar ice sheets). Global sea level has risen about 8 inches in the last 100 years, making coastal storms more damaging and accelerating erosion. It is projected to rise an additional 1 to 4 feet by 2100, and more if glaciers in Greenland or Antarctica melt especially quickly.

Regions experience different amounts of sea level rise due to differences in ocean currents, geology, and other local factors. The U.S. Gulf Coast and East Coast have experienced some of the fastest rates of sea level rise in the world. As the seas continue to rise, existing flood risks will increase.

See the interactive NOAA Sea Level Trends Map and the U.S. Climate Resilience Toolkit Map.

Extreme weather

Warmer air temperatures amplify weather cycles, just as performance enhancing drugs let baseball players hit more home runs. Scientists see this effect in weather events today.

Extreme precipitation events have produced more rain and become more common since the 1950s in many regions around the world. In the United States, the Midwest and Northeast have exhibited the strongest increases in the amount of rain falling in heavy precipitation events, increasing the risks to life and property from flooding.

Extreme heat events have also become more common. As average temperatures have increased over the last century, the hottest days are hotter than they used to be. In the United States, more daily high temperature records are being broken, and fewer daily low temperature records are being broken.

More parts of the country see days with temperatures above 95 °F. Hotter temperatures increase the risks of wildfire, drought and disease.

Ocean changes

Carbon dioxide from the atmosphere is absorbed by the oceans, creating acid in the process. Acid concentration is measured as pH (on a scale of 1 – 14), where the more acid you have, the smaller the pH value. As atmospheric concentrations of CO₂ have increased, more acid is being created. This “ocean acidification” has lowered the measured pH of the oceans. The blue line in the figure shows how pH has gone down (the ocean is more acidic) at the same time that atmospheric CO₂ concentrations have gone up (the red line).

A separate impact in the ocean is coral bleaching. This occurs when rising ocean temperatures stress corals and cause them to eject the microscopic organisms that give them their color. This can be deadly to the coral and destroy a key home and feeding ground for marine life.

Human Health

Climate change is not just an environmental problem; it’s a human health problem. Extreme heat kills more Americans each year than hurricanes, tornadoes, floods and lightning combined. Warmer temperatures affect air quality, accelerating the formation of ozone that can aggravate asthma and other respiratory illnesses. A changing climate can also expand the reach of insects carrying diseases like Lyme Disease, West Nile Virus, and Dengue Fever. Climate change also will increase the frequency or severity of certain extreme weather events, which can be deadly. As with many health impacts, young children, the elderly, those who are already sick, and those with limited access to healthcare are most at risk.

National Security

The U.S. military is concerned about direct climate impacts, such as how sea-level rise affects U.S. military bases along the coast. But military leaders are also concerned about the ways climate impacts can destabilize countries, posing new security risks and challenges. More frequent and intense droughts and floods, for instance, can disrupt agricultural productivity and food supplies, forcing population migrations that contribute to conflicts. U.S. military forces could face new security and humanitarian needs.