Global warming refers to the rise in Earth’s surface temperature caused by human activities. The increase in atmospheric temperature is driven by the “greenhouse effect,” in which gases such as carbon dioxide, nitrous oxide and methane trap heat radiating from the planet’s surface and slow its loss to space. While the Sun has played a role in past climate changes, current global warming cannot be explained by natural causes.
Since the start of the Industrial Revolution, the concentrations of these greenhouse gases in the atmosphere have increased. This is the main reason for the increase in global temperature. The most important greenhouse gas is carbon dioxide, and its concentration in the atmosphere has risen over the past 150 years because of the burning of fossil fuels.
In addition, logging and development destroy forests, wetlands, and other carbon sinks that absorb and store carbon in the soil. As a result, carbon dioxide levels in the atmosphere are now much higher than during any period in Earth’s history that has been recorded with reliable thermometers. Air bubbles trapped in mile-thick ice cores and other paleoclimate evidence indicate that atmospheric carbon dioxide never exceeded 300 parts per million in the past 1.7 billion years.
Scientists believe that if current emission trends continue, the average global temperature will rise by more than 2 degrees Celsius above the pre-industrial level by 2040. This level of warming would trigger a range of dangerous impacts on people and nature, including melting polar ice caps and glaciers, more severe wildfires, ocean acidification, habitat destruction, reduced fresh-water availability, degraded agricultural land, and the disruption and depletion of stratospheric ozone.
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