By Beatrice Omotosho

Human impacts – Anthropogenic Greenhouse gases

Humans have had an indisputable impact on climate over the last 100 years and this fact has become very clear since 1960s. This is because of the vast increase over a short period of time of short and long lived greenhouse gases (LLGHGs) namely CO2, N2O, CH4 and industrial SO₂: short lived, which all accentuate the natural greenhouse effect as they are, chemically stable and therefore persist in the atmosphere, allowing them to affect climate over decades and centuries, resulting in increasing global average temperatures due to higher radiative forcing. SO₂ is an important component of smog which can create global dimming and cause a short-term cooling effect.

All that is required is to examine the data, where the divergence in the levels of these GHGs from Pre to Post-industrial levels is evident and rather dramatic. These increases in GHGs (shown in figure 4), have come about as a result of the agricultural and industrial revolution which has led to changes in land use patterns, intense burning of fossil fuels: which breaks into the natural carbon geological cycle, high amounts of waste generation and disposal, deforestation, monoculturalisation of crops, livestock overgrazing, CFCs etc.

The data

Though there are 5 key GHGs that contribute to the greenhouse effect: H2O, CH4, N2O, CFCs: (now highly regulated due to ozone destruction) and CO2, they all contribute slightly differently due to their varying rates of radiative forcing and different feedback mechanisms. These are present; as shown by figure 1 in different concentrations, have different persistence years, different greenhouse levels of influence on the greenhouse effect and therefore on global warming potential. In a bid to not bore my readers to death, I will focus on only 3 key GHGs: H2O, CH4 and the one everyone raves about: CO2. Currently, change in global surface temperature in relation to the 1951-1980 average is 0.8 degree Celsius. Now I know we would all quite frankly prefer warmer summers, but this is certainly not the mere implication of this temperature rise.

Methane

CH4 is produced through activities such as rice cultivation, decomposition of waste, livestock farming etc and in terms of its molecular composition, is more active in the atmosphere in comparison to e.g. CO2. However though high, its atmospheric abundance does not compare to that of CO2. Current levels are shown in figure 1, and radiative forcing levels are illustrated in figure 2.

Water Vapour

This accounts for the highest amount of GHGs and is key in the intensified greenhouse effect due to the creation of a positive feedback mechanism to the climate. See I always knew there was a reason I hated showers; water is dangerous people! H2O rises as temperatures increase but so in turn does the chance of precipitation and clouds since that itself is based on temperature hence a loop is formed. This non-linearity makes it harder to account for direct effects meaning larger than anticipated/predicted changes could be seen. Current levels can be seen in Figure 1, while figure 2 shows its radiative forcing.

Carbon dioxide

Released through activities like deforestation, fossil fuel burning and generally just you know, breathing, CO2 “is the  most important long-lived forcing of climate change”, meaning more sunlight is being absorbed by the earth than is being reflected back to space (positive forcing of +1.66 ± 0.17 W m–2 shown in figure 2), hence a climate warming effect. Currently levels are at 412 ppm according to the most recent data collected in August 2019 by Mauna Loa Observatory. What’s most striking is the positive correlation between CO2and global temperature change (which sceptics constantly try to deny), which is partly due to “ the relationship between temperature and the solubility of CO2 in the surface ocean” but mainly because of the positive feedback between CO2 and climate shown in figure 3.

Conclusion

Climate is always changing due to many reasons outlined by this 4 part series, with the main natural causes that have affected global climate in the last 100 years being solar variation: to a small extent, El Niño events and volcanic eruptions: both of a more noticeable effect. However, these are can only account for the decadal variations, the real trend itself can only be explained by anthropogenic GHG emissions which have continued to increase at unprecedented rates since the 1900s. Until the 1980s, it was difficult to separate these natural and human causes from the trend observations, now we can see this through the diversion of the blue and pink areas on figure 5 and the continuance of the actual observation line in the trend of the pink area line.

Following this date, it is almost certain that this new trend is due to global human activities such as globalisation, increases and changes in the patterns of consumption, conversion of green and blue carbon pools etc and the effect this has had on global GHG levels leading to an ‘enhanced anthropogenic greenhouse effect’ that is increasing global average temperatures. It is therefore with high confidence that I conclude that this trend is as result of human activity, now you can really tell that sceptic to stick it!