Climate change is one of the greatest threats to human health1 and wildlife conservation2,3 of the 21st century. Social protests calling for action on the climate change issue are increasing across world’s regions4. The consequences of human-induced climate change are well-described5 and so are its anthropogenic causes6; but how does climate change actually work?
Our planet is constantly being washed with many different types of light waves coming from the sun. These include x-rays, ultraviolet light, infrared light, visible light, microwaves, etc. When these different types of light reach earth, about a third gets reflected by the clouds, while some gets absorbed by the layers in our atmosphere – notably, the ultraviolet light gets absorbed by the ozone layer7. This leaves about half of the light, mostly infrared and visible light, reaching the earth’s surface and getting absorbed by the sea, land and vegetation which, heating up, release most of the energy back in the form of infrared light.
Up to 99% of the earth’s atmosphere consists of nitrogen (N2) and oxygen (O2), which do not react to infrared light – if it were for them alone, no heat would be trapped on earth and life as we know it wouldn’t exist. However, air contains also a variable amount of water vapour (H2O) that absorbs most of the infrared light. When water vapour molecules take in the infrared light, they enter a new, “excited”, energy state for a few milliseconds. If they collide with nitrogen or oxygen molecules during this excited state (and they do as collisions occur 10 million times a second), they can transfer their extra energy to the nitrogen or oxygen molecules, which warm up. This is the mechanism that keeps the earth tolerably warm.
To our interest, water vapour does not absorb all frequencies of the infrared light, instead a few frequencies slip through – which is good otherwise the earth would be unbearably hot. However, by chance carbon dioxide (CO2) absorbs just those frequencies, closing the escape valve. In other words, carbon dioxide blocks the outflow of infrared radiations (i.e., heat) from the earth. This is why the increasing levels of CO2 in the atmosphere are inevitably linked to rises in the Earth’s surface temperature – which above a certain threshold (1.5 °C) will lead to potentially disastrous consequences8.
Figure and description credits: Mann, C.C., 2018. The Wizard and the Prophet: Two Remarkable Scientists and Their Dueling Visions to Shape Tomorrow’s World. Knopf.
There are also other types of climate-change altering gasses that humans produce, including methane, nitrous dioxide, and a bunch of fluorine-containing gasses. These actually absorb more infrared radiation than CO2, however they are not present in large quantities. The reason why cow burps and farts are bad for climate change9 is because methane has as much as eight times the effect on climate as an equivalent amount of CO2 – nonetheless, methane molecules will remain in the atmosphere for just a few decades, compared with centuries or millennia of CO2.
Global carbon emissions have more than tripled over the last sixty years (1960-2018)10. Concurrently, levels of CO2 particles in the atmosphere have since increased significantly11, and so has temperature (by ~1°C since the 1950s)12.
The graph shows average annual global temperatures since 1880 compared to the long-term average (1901-2000). The zero line represents the long-term average temperature for the whole planet; blue and red bars show the difference above or below average for each year. Figure & description credits: https://bit.ly/2bGmphJ
What’s the difference between climate change and global warming?
“Global warming refers only to the Earth’s rising surface temperature, while climate change includes warming and the side effects of warming—like melting glaciers, heavier rainstorms, or more frequent drought. Said another way, global warming is one symptom of the much larger problem of human-caused climate change.”
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- Thomas, C.D., Cameron, A., Green, R.E., Bakkenes, M., Beaumont, L.J., Collingham, Y.C., Erasmus, B.F., De Siqueira, M.F., Grainger, A., Hannah, L. and Hughes, L., 2004. Extinction risk from climate change. Nature, 427(6970), p.145 https://doi.org/10.1038/nature02121
- Cook, J., Oreskes, N., Doran, P.T., Anderegg, W.R., Verheggen, B., Maibach, E.W., Carlton, J.S., Lewandowsky, S., Skuce, A.G., Green, S.A. and Nuccitelli, D., 2016. Consensus on consensus: a synthesis of consensus estimates on human-caused global warming. Environmental Research Letters, 11(4), p.048002 https://doi.org/10.1088/1748-9326/11/4/048002