Global warming is the long-term rise in the average temperature of the Earth's climate system. The term "global warming" was first created by Wallace Smith Broecker in 1975. This commonly refers to the mainly human-caused increase in global surface temperatures and its projected continuation. There were prehistoric periods of global warming, but observed changes since the mid-20th century have been much greater than those seen in previous records covering decades to thousands of years. Temperatures today are 0.74 °C (1.33 °F) higher than 150 years ago. Many scientists say that in the next 100–200 years, temperatures might be up to 6 °C (11 °F) higher than they were before the effects of global warming were discovered.
Among the Greenhouse gases, the concentration and increase of carbon dioxide in the atmosphere appears to be the main cause of global warming. When people cut down many trees (deforestation), this means less carbon dioxide is taken out of the atmosphere by those plants. Coal-burning power plants, car exhausts, factory smokestacks, and other man-made waste gas vents give off about 23 billion tons of carbon dioxide and other greenhouse gases into the Earth's atmosphere each year. The amount of CO2 in the air is about 31% more than it was around 1750. About three-quarters of the CO2 that people have put in the air during the past 20 years are due to burning fossil fuel like coal or oil. The rest mostly comes from changes in how land is used, like cutting down trees.
As the Earth's surface temperature becomes hotter the sea level becomes higher. This is partly because water expands when it gets warmer and warm temperatures make glaciers melt. The sea level rise causes coastal areas to flood. Weather patterns, including where and how much rain or snow there is, will change. Deserts will probably increase in size. Colder areas will warm up faster than warm areas. Strong storms may become more likely and farming may not make as much food. Global warming means that Antarctica and Greenland ice sheets are melting and the oceans are expanding.
Generally, impacts on human health will be more negative than positive. Impacts include the direct effects of extreme weather, leading to injury and loss of life and indirect effects, such as undernutrition brought on by crop failures. Temperature rise has been connected to increased numbers of suicides. Links have been made between a wide range of violent behaviour including fist fights, violent crimes, civil unrest, and wars. Climate change may also lead to new human diseases.