Global warming is caused by the increase in greenhouse gases, mainly carbon dioxide and methane, which trap heat in the atmosphere. Human activity is the main cause of this increase, with the burning of fossil fuels and the production of cattle being significant contributors. As temperatures rise, natural systems such as permafrost and ocean sequestration fail, further accelerating global warming.
Global warming is a term generally used to describe the shift in the average temperature of the earth’s surface since the mid-20th century. The causes of global warming are the subject of some debate, although there is broad consensus among the scientific community, formalized in a report by the Intergovernmental Panel on Climate Change, that most of the increase in temperature since the mid-20th century is the result of human activity. Prior to the mid-20th century, the primary causes of global warming were natural events, such as volcanic activity and increased solar radiation.
One of the main causes of global warming is the increase in certain greenhouse gases, which absorb infrared radiation and trap the heating energy in the atmosphere. Carbon dioxide is a major greenhouse gas, trailing just behind water vapor in quantity, and carbon dioxide levels in the atmosphere have increased nearly 40% since the industrial revolution. Carbon dioxide is released by humans in different contexts, for example in the United States about 40% of carbon dioxide emissions come from the production of electricity by burning fossil fuels, while cars are responsible for another 33% of emissions.
Although not as prevalent in the atmosphere, methane is another greenhouse gas responsible for global warming. Methane is about 20 times as effective at trapping heat as carbon dioxide, and methane levels have increased nearly 150 percent over the last century. A large amount of methane is released through the production of fossil fuels and through the large-scale production of cattle. Methane is also produced in rice paddies, and as global demand for rice has increased, this single crop has contributed significantly to methane production.
While some causes of global warming can be linked directly to human activity, others occur as cascading effects. As the average temperature of the planet rises, some systems fail and can increase the rate of global warming. For example, much of the planet’s northern latitude is covered in permafrost, a kind of solid, frozen ground. This permafrost has acted as a sink for many greenhouse gases, including carbon dioxide and methane, for tens of thousands of years, and as temperatures rise, the permafrost that has been frozen for more than 30,000 years has begun to thaw. As well as causing the soil to shift in often dangerous ways, this also releases gases into the atmosphere, further accelerating the global warming process.
Other cascading causes of global warming include the ice-albedo effect and reduced sequestration by the oceans. As temperatures rise, the ice on the planet melts, reducing the amount of highly reflective land that has minimized solar absorption in the past and increasing the rate of melting. As the oceans warm, nutrient densities decrease, leading to decreased populations of diatoms, which in turn reduces the oceans’ ability to sequester carbon. While there are other small contributors to global warming, it is largely the release of carbon dioxide and methane into the atmosphere that is thought to be responsible for the steadily accelerating warming taking place across the globe.
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