CLIMATE CHANGE AND ATMOSPHERIC CIRCULATION
By Vithusan Kuganathan
It’s undeniable at this point that humans are having a significant negative impact on the earth. Many argue that climate change is a natural phenomenon – the earth has warmed up in the past and is continuing to do so. However, the IPCC – the Intergovernmental Panel on Climate Change has plenty of evidence exemplifying the extent of anthropogenic climate change. The full extent of the future impacts is still up for debate, however some of the impacts are starting to take shape, such as melting ice caps. Others are still contentious, such as the impacts on atmospheric circulation.
To give some brief background on the theories surrounding atmospheric circulation, the prevalent model of atmospheric circulation is the tricellular model. This essentially divides the northern and southern hemisphere into three cells – the Hadley, Ferrel and Polar cells. Where the two Hadley cells meet is knows as the ITCZ – the Intertropical Convergence Zone, the shortest distance between the sun and the surface of the Earth. The way this model actually works is quite interesting. The UV rays received from the sun aren’t sufficient in and of themselves to warm air. These UV rays reach the Earth’s surface. As a cooling mechanism of sorts, the Earth’s surface releases IR (infra-red radiation), heating up the surrounding air, causing a decrease in density, as particles have more kinetic energy so that they spread out more. Decreasing density means it is less dense than the surrounding air, leading to this parcel of air rising. This initiates the circulation.
As the air rises, it begins to spread out, at high altitudes, away from the ITCZ – an epicentre of sorts. At roughly 30 degrees N, the air begins to sink due to the increasing density. This is where the Ferrel cell begins and is the sub-tropical jet stream. This air continues moving North to around 60 degrees N, where it encounters cold winds from the poles. Due to the parcel of air from the Ferrel cell having a lower density than the air from the poles, it rises and the air from the poles sinks and the cold air sinks. This is a very brief description of the tri-cellular model and how it can give way to atmospheric circulation. However, what is more interesting is how it can give way to distinct climatic characteristics. At the ITCZ, there is rising air as I mentioned before. Rising air experiences adiabatic cooling and this creates large cumulonimbus clouds. Due to suspended water vapour in the parcels of air, these clouds give way to precipitation. This is known as a depression system. Yet, as air sinks it experiences adiabatic warming. This warming enables parcels of air to retain more moisture, leading to dry conditions. This is why some deserts – sandy and polar are found at these areas of sinking air, as this sinking air generates arid conditions. These areas of sinking air are called anti-cyclones.
Moving onto the topic of discussion – climate change. An area of discussion concerning atmospheric circulation is the potential enlargement of the Hadley cell which could contribute to drastic changes to climatic conditions around the world. This idea of poleward migration was initially introduced during the 2003 European heatwave. The descending section of the Hadley cell had seemingly migrated as far north as continental Europe contributing to more than 20,000 deaths, due to the heatwave it brought. This widening of the Hadley cell has seemingly been triggered by the increase in Greenhouse Gas emissions, having a more pronounced impact in the Boreal Autumn. However, the impacts of an expanding Hadley cell could be disastrous, primarily due to the anticyclones it creates during the northern hemispheres summer. Due to these anticyclones, there would be an increasing level of meteorological drought. Furthermore, there would be flooding elsewhere, due to the introduction of more depression systems in those areas, leading to increased precipitation.
One of the most unpredictable elements of climate change is the impact it may have on the following items: the walker circulation, a circulation of water in the South Pacific, and the resulting weather phenomenons - the El Niño events as well as the La Niña events. This is primarily due to the ambiguity to the different theories surrounding their existence (for El Niño and La Niña).
Overall, climate change still remains one of the biggest existential threats that is being posed to mankind. Drought in particular has had devastating impacts across the world, such as in the horn of Africa, where it has led to famine and in some have been forced to leave their homes and their country. Therefore, something needs to be done to combat climate change before it has dramatic and irreversible impacts on society as we know it.
Sources:
https://journals.ametsoc.org/doi/full/10.1175/2009JCLI2794.1
https://www.sciencedirect.com/science/article/pii/S2095927318301919