What Is Climate Change

Overview

Climate change is the defining environmental challenge of our time. It refers not just to rising temperatures but to a cascade of interconnected changes: melting ice sheets, rising sea levels, more frequent extreme weather events, shifting ecosystems, and ocean acidification. While Earth's climate has changed naturally throughout its 4.5-billion-year history, the current rate of change is unprecedented.

The Greenhouse Effect

The greenhouse effect itself is natural and essential — without it, Earth's average temperature would be about -18°C (0°F) instead of the habitable 15°C (59°F). The problem is that human activities have intensified this effect by dramatically increasing the concentration of greenhouse gases:

• Carbon dioxide (CO₂): From burning fossil fuels (coal, oil, natural gas) and deforestation — responsible for about 75% of warming
• Methane (CH₄): From agriculture (livestock, rice paddies), landfills, and natural gas leaks — about 16% of warming
• Nitrous oxide (N₂O): From agricultural fertilizers and industrial processes

Observed Effects

Global average sea levels have risen about 20 cm (8 inches) since 1900 and the rate is accelerating. Arctic sea ice is declining by about 13% per decade. Extreme weather events — heatwaves, droughts, intense hurricanes — are becoming more frequent and severe. Coral reefs are experiencing mass bleaching events. Many species are shifting their ranges toward the poles or to higher elevations.

What Can Be Done

Mitigation involves reducing greenhouse gas emissions through renewable energy, energy efficiency, electrification of transport, and protecting forests. Adaptation involves preparing for the changes already locked in — building sea walls, developing drought-resistant crops, and improving early warning systems for extreme weather.