Man made climate change will have a growing global impact over the coming century. Why is this? How big could the impact be?
The greenhouse gas effect is somethiing that has been know about for more than 150 years. Eunice Foote published a paper on it in 1856 (American Journal of Science and Arts) and this was followed in 1859 in a series of studies published by John Tyndall. These researchers established that CO2 and other gases would trap heat in the atmosphere by absorbing radiation from the sun.
While these researchers established the principle behind the greenhouse effect, the first person to try to accurately quantify the effect on climate was the chemist Svante Arrhenius in his 1896 paper (Philosophical Magazine and Journal of Science). At the time Arrhenius and other colleagues were more interested in the factors that led to the ice ages and interglacials. Although the industrial revolution was well under way in Europe and America, and they were aware of the possible impact of industrial carbon dioxide emissions, carbon dioxide levels were still low compared with now and they did not see an immediate danger. Arrhenius identified that a doubling of carbon dioxide in the atmosphere could raise temperatures by between 5 and 6 degrees celsius, depending on latitude. Todays modelling is much more sophisticated but the predictions are in the same ball park and Arrhenius correctly predicted that warming would be greatest at higher latitudes.
The scientific community first started warning of the dangers of greenhouse gas emissions and climate change in the 1950s and 60s and around the time of the first climate conference in 1979 there is evidence that oil companies had already completed secret research which concluded that while the impact of burning fossil fuels would be relatively mild by the early 2000s it would be catastrophic by the 2060s. (1980 task force presentation).
Carbon dioxide levels in the atmosphere are normally governed by two carbon cycles. The fast bilogical one mediated by life where respiration by plants and animals to extract energy from carbon compounds by oxidation puts carbon dioxide into the air. Photosynthesis by plants during daylight reverses the process using light to turn carbon dioxide into sugars to store energy. Some carbon is removed from the atmosphere by dead plants and animals that become buried in bogs or fall to the bottom of the sea.
The second is a slower geological cycle where carbon dioxide reacts with minerals in rocks and the sea to create carbon compounds which become buried in soil and sea sediments. This carbon is taken down by the subduction process of plate tectonics but later released into the atmosphere by volcanic eruptions.
Image credit: Biogeochemical cycles: Figure 3 by OpenStax College, Biology, CC BY 4.0; modification of work by John M. Evans and Howard Perlman, USGS
Neither of these cycles is exactly in balance. The biological cycle normally removes carbon dioxide from the atmosphere over time. The geological cycle generally returns it via volcanism. Over thousands of years atmospheric carbon fluctuates, times of vigorous plant growth removes carbon but results in lower temperatures which reduce plant growth and the tendency for carbon dioxide to be removed. At the same time volcanoes are returning CO2 to the atmosphere and eventually temperatures start to rise again. This process amplifies fluctuations in the sun's radiation caused by variations in the earth's orbit (Malankovich Cycles).
Image credit: "Threats to biodiversity: Figure 1" by OpenStax College, Biology, CC BY 4.0
These changes normally take place over thousands of years. However, in the last two hundred years humans have disrupted this cycles by releasing buried fossilised carbon in the form of coal, oil and gas combustion and also reduced the bioligical cycles ability to remove carbon from the atmosphere through deforestation.
Climate.gov