Definition
Global warming is the long-term increase in the Earth's average surface temperature. It is caused primarily by the accumulation of greenhouse gases in the atmosphere, which trap heat that would otherwise escape into space.
Global warming is the central mechanism behind the broader phenomenon of climate change. The two terms are related but distinct: global warming names the rising temperature itself, while climate change describes the wider set of consequences that follow from it.
Why it matters
How it works
The atmosphere naturally keeps the Earth warm enough to support life — without greenhouse gases the planet would be frozen. The problem is one of degree. By burning fossil fuels and clearing forests, human activity has sharply raised the concentration of these gases.
The extra gases strengthen the heat-trapping effect, so the planet absorbs more energy than it releases. The surplus energy warms the land, oceans, and atmosphere. Because carbon dioxide remains in the air for a long time, the warming continues until emissions are brought close to zero.