How and why have global warming and climate change occurred?
The how and the why of climate change are very tightly linked, so tightly linked people as far back as 1896 had figured out the basics of how it works. Earth’s atmosphere keeps the world warm by trapping heat. It does this in a way similar to the way a greenhouse works (thus the name “greenhouse effect”). Sunlight (and warmth) can come through the atmosphere in the day time and warms up the land and sea areas. At night cooling occurs, with the heat escaping into the atmosphere, some of that leaks out into space again, but not all because the atmosphere traps some of the heat. The key bit of the atmosphere that traps the heat are the greenhouse gases.
Natural greenhouse gases are water vapor, carbon dioxide, methane, ozone and nitrous oxide. These chemicals are an important part of the world’s natural cycles. They cycle between the atmosphere, the ocean, soils and rocks. Human activities have changed those cycles, meaning more greenhouse gases have entered the atmosphere, trapping more heat and leading to global warming and climate change.
Many human activities influence climate relevant cycles, but two of the most important are to do with carbon dioxide and methane. Fossil fuels contain carbon dioxide locked up millions of years ago, by bringing it to the surface and burning the fossil fuels human activity short circuits natural weathering and other cycles, creating one of the major sources of the excess carbon dioxide that is creating climate change.
Agriculture is also a major contributor to climate change, producing about a quarter of all current greenhouse gas emissions. These emissions come from the fuels used by farmers, but also because of emissions from rice paddies and livestock, which produce methane. A particularly powerful greenhouse gas, over a 20-year period methane is 80 times more potent at warming than carbon dioxide. On top of this, the removal of native vegetation, like forests, to create space for agriculture reduces the amount of carbon drawn out of the atmosphere and stored in trunks and roots as trees grow (known as sequestration).
As you can see there are many interconnected ways that human activities are influencing the biogeochemical cycles of Earth and thereby contributing to climate change.