Notes

Long-term changes in temperature and weather patterns are referred to as climate change. These changes could be caused by natural processes, such oscillations in the solar cycle. But since the 1800s, human activities—primarily the combustion of fossil fuels like coal, oil, and gas—have been the primary cause of climate change. Fossil fuel combustion produces greenhouse gas emissions that serve as a blanket around the planet, trapping heat from the sun and increasing temperatures. Carbon dioxide and methane are two examples of greenhouse gas emissions that are contributing to climate change. These are produced, for instance, while burning coal or gasoline to heat a building. Carbon dioxide can also be released during forest and land clearing. Methane emissions are primarily produced by waste landfills. Among the major emitters are energy, industry, transportation, buildings, agriculture, and land use.

In a nutshell, carbon is mostly found in the air as carbon dioxide (CO 2 ).
CO 2 start text, H, C, O, end text, start subscript, 3, end subscript, start superscript, minus, end superscript—gas that dissolves in water and interacts with water molecules to generate bicarbonate—CO 2 start text, C, O, end text, start subscript, 2, end subscript. Organic molecules are created from carbon dioxide or bicarbonate during photosynthesis in terrestrial plants, microorganisms, and algae. Through food chains, photosynthesizing organisms produce organic compounds that are then changed back into carbon dioxide gas through cellular respiration. When organic material from living things is buried deep underground or sinks to the ocean's floor and becomes sedimentary rock, it stores organic carbon for an extended period of time. This carbon is released back into the carbon cycle through volcanic activity and, more recently, human burning of fossil fuels. Despite the slow geologic timescale over which fossil fuels develop, human emission of the carbon they contain—as CO 2 CO 2 is on a very quick timeframe (start text, C, O, end text, start subscript, 2, end subscript).