In common usage, climate change describes contemporary global warming—the ongoing increase in global average temperature—and its impacts on Earth's climate system. Climate change in its broad sense also includes previous long-term changes to Earth's climate. The current rise in global average temperature is more rapid than previous changes, and is primarily caused by humans. Burning fossil fuels adds greenhouse gases to the atmosphere, most importantly carbon dioxide (CO2) and methane. Smaller contributions come from agriculture, industrial processes, and forest loss. Greenhouse gases warm the air by absorbing heat radiated by the Earth, trapping the heat near the surface. Greenhouse gas emissions amplify this effect, causing the Earth to take in more energy from sunlight than it can radiate back into space.
Due to climate change, deserts are expanding, while heat waves and wildfires are becoming more common. Increased warming in the Arctic has contributed to melting permafrost, glacial retreat and sea ice loss. Higher temperatures are also causing more intense storms, droughts, and other weather extremes. Rapid environmental change in mountains, coral reefs, and the Arctic is forcing many species to relocate or become extinct. Climate change threatens people with food and water scarcity, increased flooding, extreme heat, more disease, and economic loss. Human migration and conflict can also be a result. The World Health Organization (WHO) calls climate change the greatest threat to global health in the 21st century. Even if efforts to minimise future warming are successful, some effects will continue for centuries. These include sea level rise, and warmer, more acidic oceans.Many of these impacts are already felt at the current 1.2 °C (2.2 °F) level of warming. Additional warming will increase these impacts and may trigger tipping points, such as the melting of the Greenland ice sheet. Under the 2015 Paris Agreement, nations collectively agreed to keep warming "well under 2 °C". However, with pledges made under the Agreement, global warming would still reach about 2.7 °C (4.9 °F) by the end of the century. Limiting warming to 1.5 °C will require halving emissions by 2030 and achieving net-zero emissions by 2050.
Making deep cuts in emissions will require switching away from burning fossil fuels and towards using electricity generated from low-carbon sources. This includes phasing out coal-fired power plants, vastly increasing use of wind, solar, and other types of renewable energy, and taking measures to reduce energy use. Electricity generated from non-carbon-emitting sources will need to replace fossil fuels for powering transportation, heating buildings, and operating industrial facilities. Carbon can also be removed from the atmosphere, for instance by increasing forest cover and by farming with methods that capture carbon in soil. While communities may adapt to climate change through efforts like better coastline protection, they cannot avert the risk of severe, widespread, and permanent impacts.
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