1. Climate Starts with Energy Balance

Climate is the long-term pattern of temperature, precipitation, wind, and seasons in a region. Weather is what happens today; climate is the pattern over many years. To understand climate change, begin with energy balance.

Sunlight enters the atmosphere and warms Earth's surface. The surface gives off heat as infrared radiation. Greenhouse gases such as water vapor, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) absorb some of that outgoing heat. This natural greenhouse effect keeps Earth warm enough for life.

The problem is the enhanced greenhouse effect. Burning coal, oil, and natural gas adds CO2 that was stored underground for millions of years. Agriculture, landfills, and fossil fuel leaks add methane. Fertilizer use can add nitrous oxide. More heat-trapping gases shift Earth's energy balance, raising average global temperature.

The GED® usually does not ask you to debate climate science. It asks you to read evidence: rising CO2, rising average temperatures, shrinking glaciers, sea-level rise, earlier seasonal events, and changing species ranges. The reasoning skill is to connect a trend with a mechanism.