The world’s temperature is warming faster than ever before. That’s climate change, and it threatens human health and all life on Earth.

Climate change is caused by human activities, especially the burning of fossil fuels (oil, gas, and coal). When these fuels burn, they release greenhouse gases that act like a blanket, trapping heat and warming the atmosphere. Concentrations of these greenhouse gases have increased over the past 150 years, and most of this increase can be attributed to human activity.

Humans have always experienced climatic changes on relatively short timescales: seasons, years, and decades. But full appreciation of the magnitude and nature of these climatic changes did not begin until the 19th century.

The most important cause of anthropogenic climate change is the emission of long-lived greenhouse gases, especially carbon dioxide (CO2). The atmospheric concentration of CO2 has doubled over the last 100 years due to the burning of fossil fuels, and the associated warming of the atmosphere has many secondary effects. For example, melting ice and snow causes glaciers to recede, and the expansion of seawater as it warms leads to rising sea levels.

The impact of climate change varies by region, with poorer communities experiencing higher rates of extreme weather events. The wealthy nations that emitted the lion’s share of historical greenhouse gases must lead the way in reducing emissions, but they cannot do it alone. To succeed, they must partner with developing countries to develop clean energy technologies and share the burden of reducing emissions.