On Climate Change

 “There is no question that global climate change is happening; the only arguable point is what part humans are playing in it.” – David Attenborough 

To what extent do you agree with the statement?

Climate change refers to fluctuations in the Earth’s temperature, consisting of both global warming and global cooling. Both natural and human forcings have led to climate change on different timescales. However, in recent years, on a human timescale, the impact of anthropogenic activities on the climate has had increasing significance. Therefore, I agree that while climate change is definitely occurring on a geological timescale with natural forcings, such as the Milankovitch Cycle, the influence of humans on climate change is increasing, due to changes in land use and urbanisation causing global warming.

Throughout the geological timescale, the global climate has experienced fluctuations in temperature, from periods of stability to periods of great instability, and global warming and cooling due to natural forcings. These have caused changes to the climate on a longer timescale beyond humans. The Milankovitch cycle is a natural forcing that highlights how precession, axial tilt and eccentricity affect the distribution and intensity of insolation received on the Earth’s surface. For example, eccentricity refers to the path of the Earth’s orbit around the Sun, ranging from circular to elliptical. When the orbit is circular and of lower eccentricity, differences in insolation received at perihelion, when Earth is closest to the Sun, and aphelion, when the Earth is farthest from the Sun, is the least. This leads to lower variations between Southern Hemisphere summer and Northern Hemisphere summer. At 3% difference in distance between perihelion and aphelion, difference in insolation received during July in Northern Hemisphere summer and during January in Southern Hemisphere is at 6%. However, as eccentricity increases, there could be a 20% to 30% difference between insolation received at perihelion (NH Summer) and aphelion (SH summer), affecting global temperatures. However, such natural forcings occur over a longer timescale, as evidenced by eccentricity occurring over a 100 000 year cycle, therefore their effect on the climate is seen to be more gradual. Such forcings also lead to fluctuations in temperature where both global warming and global cooling occur. Therefore, it is evident that natural forcings such as the Milankovitch cycle play a significant role in climate change over a longer timescale.

Global climate change is also due to other natural forcings that occur over a shorter timescale. This is evidenced by sunspot activity, where sunspots vary over an 11-year cycle. During periods of intense sunspot activity, global temperatures were recorded to be approximately 1°C higher, as the areas around the darker sports on the sun radiate more solar energy, creating an area of intense heating. Isolated events such as volcanic eruptions serve also to affect the climate, such as the 1991 Mount Pinatubo eruption ejecting 15 million tonnes of sulphate aerosols into the stratosphere, where aerosols reflected insolation and created a ‘global dimming effect’, with global temperatures decreasing by 0.6C for 2 years. Therefore, it can be seen that natural forcings lead to global warming and cooling, and can occur over shorter timescales, making the change in climate more sudden and causing fluctuations in temperature over a short period of time.

However, in the recent years, anthropogenic activity has led to changes in land use, affecting surface albedo and causing rapid global warming. Increased urbanization involves the large-scale concretisation of the Earth’s surface, causing a fall in albedo. This has created the ‘urban heat island effect’, where concrete with an albedo of 0.55 absorbs insolation, heating the Earth’s surface. Increases in global temperatures brought about by industrialisation which increased the concentration of greenhouse gases in the atmosphere lead to melting of ice caps and subsequent evaporation of ocean waters. Ice has high albedo of 0.7, compared to darker ocean waters (albedo: 0.07), therefore global warming leads to less insolation reflected and more absorbed, setting up a positive feedback cycle and continuous melting of ice. This releases permafrost and methane stored in ice, and methane as a greenhouse gas further contributes to enhanced greenhouse effect, causing global warming. This accounts for the effect of human activity on climate change. Therefore, it is apparent that in the recent years, human activities has led to a continuous warming of Earth’s surface, occurring at a rate faster than that of natural forcings.

Furthermore, human activity has led to increase in emissions of greenhouse gases, leading to the enhanced greenhouse effect due to increased concentrations of greenhouse gases in the atmosphere. This is due to industrialisation, where the burning of fossil fuels and deforestation decreases carbon stores and releases carbon dioxide (CO2) into the atmosphere. Before the Industrial Age, CO2 concentrations in the atmosphere were 290 ppm +/- 10ppm. Following industrialization, this increased to 390ppm, and this increase has been concentrated in the last 30 years. While natural forcings lead to global warming and cooling, human activity has led to continuous warming, and this is evidenced by Michael Mann’s ‘hockey stick graph’ (Figure 1). The large deviation in temperatures is due to the rise of the Anthropocene, where increased greenhouse gas emissions lead to enhanced greenhouse effect. Therefore, it is evident that human activity and its impact on climate change is more significant in a human timescale.

Figure 1, Michael Mann’s hockey stick graph

In conclusion, climate change has occurred due to both natural and human forcings. Natural forcings lead to periods of both global warming and cooling, and is more gradual over a longer, geological timescale. However, in recent years, the impact of human activity on climate has been increasingly significant on a human timescale, where urbanisation and industrialisation affect surface albedos, causing increased global warming and a continuous increase in global temperatures. Therefore, humans play a larger role in global warming on a human timescale. This rise in global temperatures has led to multiple impacts ranging from melting ice caps and intense warming, and it is therefore imperative that “humans work together to tackle climate change to ensure sustainable development”, as mentioned by #SDG13 in the Sustainable Development Goals, thereby highlighting the impact of climate change and how it would hinder our pursuit of sustainability. Global warming could compromise the ability of future generations to meet their own needs, as resources and funds would have to be invested into tackling climate change, and resources are diverted away from the pursuit of sustainable development, hence it is imperative climate change is tackled in order to ensure #SDG13 is not compromised.

Christabelle Kam (18-I2)

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