Greenhouse gases from human activities are the most significant driver of observed climate change since the mid-20th century.

Concentrations of carbon dioxide and other greenhouse gases in the atmosphere have increased since the beginning of the industrial era. Almost all of this increase is attributable to human activities. Greenhouse gases are transparent to incoming (short-wave) radiation from the sun but block infrared (long-wave) radiation from leaving the earth's atmosphere. This greenhouse effect traps radiation from the sun and warms the planet's surface. As concentrations of these gases increase, more warming occurs than would happen naturally. Historical measurements show that the current global atmospheric concentrations of carbon dioxide are unprecedented compared with the past 800,000 years, even after accounting for natural fluctuations. An increase in the atmospheric concentrations of greenhouse gases produces a positive climate forcing, or warming effect. To avoid global warming, it is necessary to reduce greenhouse gas emissions. The best way is to commit to renewable energies, which generate clean electricity without harming the environment or polluting the air. Renewables also help preserve the oceans and forests, which are natural carbon sinks absorbing some of the carbon dioxide.