Global warming is the long-term increase in Earth’s surface temperature caused by increasing levels of heat-trapping greenhouse gases in our atmosphere. These gases are released when fossil fuels like oil, coal and natural gas are burned for energy in homes, factories and vehicles. The gases wrap around the Earth, trapping the sun’s heat and slowing its radiation back to space. This process, known as the greenhouse effect, is essential to life on our planet, but human activities are now changing its climate faster than any other time in recorded history.

Scientists have shown that the greenhouse gases created by burning fossil fuels (carbon dioxide, methane, nitrous oxide and chlorofluorocarbons) are responsible for the recent increase in Earth’s average temperature. These gases are causing the Earth to warm more rapidly than it has in the past 1,000 years, and more quickly than it has since the Industrial Revolution began in 1800.

The warming climate is already having many negative impacts on people and ecosystems. Warmer temperatures are affecting global food production and triggering more wildfires. They are also affecting water supplies and lowering glacier and snowpack levels. Warmer weather is raising the transmission rate of water-borne diseases like leptospirosis, campylobacter and cryptosporidiosis.

Everyone must take action, but the countries and people that produce most of the emissions have a greater responsibility to act first. The top six emitters produce more than half of the world’s greenhouse gases, and the 45 least developed nations account for only 3 percent.