Climate change is a threat to the natural world and human civilization. It is caused by changes in the Earth’s energy balance — its net incoming and outgoing solar radiation. Most incoming solar energy is absorbed by the Earth and its atmosphere, and a small amount is reflected back into space. Greenhouse gases absorb some of the outgoing energy, increasing the Earth’s surface temperature and warming its lower atmosphere. Other atmospheric constituents, such as sulfates and aerosols, exert offsetting cooling effects.
Each increment of warming results in a series of hazards that increase risks for people and nature alike: heat waves lead to illness and death, flooding from rising sea levels disrupts communities, severe droughts leave lands unproductive, wildfires burn forests and homes, and changing weather patterns reshape ecosystems. These climate-driven threats are more pronounced for the most vulnerable – those who live in poorer, less developed countries.
The planet has warmed 1.1 degrees Fahrenheit since the preindustrial era began 250 years ago, and could reach the worst-case scenario of 4 degrees Celsius if we do not curb our carbon emissions. The world’s poorest countries – which contributed least to the problem – are already struggling with its impacts, such as decreased crop yields and food insecurity.
Scientists measure Earth’s climate by studying samples from places like lakes, oceans, and Antarctica. They drill down and take cylinder-shaped samples called sediment cores or ice cores that contain layers of ancient air. By analyzing the chemical composition of these layers, scientists can see what the climate was like in the past. The newest data show that temperatures have been warming rapidly over the last century.