LOPANG THATO SETHIBE
TITLE: IS GLOBAL WARMING REVERSIBLE?
IS GLOBAL WARMING REVERSIBLE?
One of the biggest problems the world is facing today is global warming of which the leading cause is the human expansion of the greenhouse effect. Global warming is the gradual increase in the average temperature of the Earth’s surface and its oceans, and the statistics show that in 2016 the earth’s temperature was 0.94°C warmer than the 20th century. Gases responsible for the warming that occurs when the atmosphere traps heat radiating from the earth, that is the greenhouse effect are water vapour, carbon dioxide which is released through volcanic eruptions, burning of fossil fuels and deforestation, methane, nitrous oxide and chloroflourocarbons (Oreskes, 2004). As these greenhouse gases accumulate, extra heat is stored in the ocean resulting in the thermal expansion of water which causes a rise in the global mean seal level (Bouttes et al, 2013), the polar ice melts contributing also to rise in sea levels ( Wu et al, 2014) which may lead to flooding. Agricultural productivity is also affected as the crops will have to adapt to the changing climate as some areas will get drier and others wetter and there may be increased occurances of natural disasters such as severe storms and drought. The most dominant component of the greenhouse gas is carbon dioxide and as such the various proposals of climate mitigation are aimed at reducing carbon dioxide emissions (Wu et al, 2014) of which may not be sufficient. Due to this strategies such as geoengineering have been developed which is aimed reducing global warming and stabilizing the global climate. The proposed solar radiating management geoengineering methods do not reverse global warming but rather reduce the effects of anthropogenic global warming.
Global warming occurs due to the imbalance between the heat received by the Earth and the heat re-radiated back into space so to combat this, technologies that enhance outgoing long-wave radiation and cooling the earth down are developed. Geoengineering is defined as ” technological efforts to stabilize the climate system by direct intervention in the energy balance for reducing global warming” by Ming et al, (2014). According to Wu et al, (2014) the geoengineering technologies fall into two categories, the solar radiation management and the carbon dioxide removal. The major solar radiation management geoengineering proposals include space mirrors, sulphate aerosols and cloud whitening.
The idea of the space mirrors is to send numerous man-made mini-eclipses that will obscure the sun, the orbit giant mirrors deflects sunlight back into space (Angel, 2009). Early, (1989) proposed the idea of reducing solar radiation by placing a deflector of 1400km at the first Lagrange launched from the moon. According to Ming et al, (2014) this idea has poses huge unintended consequences and does not guarantee a rapid reversibility.
Sulphur aerosols have a cooling effect as they block sunlight. Burning of fossil fuels and coal introduces sulphur dioxide in the lowest levels of the atmosphere and together with other troposheric aerosols have both the direct and indirect cooling effects (Ming et al, 2014). According to Rasch, (2008) efficient cooling effect can be accomplished by 1-5 million tons of small particles of sulphur dioxide in the stratosphere as sulphates in the stratosphere have less resilient time as compared to those in the troposphere. This idea proposes increased emission of sulphur dioxide, but not the removal of carbon dioxide, thus global warming continues as the greenhouse effect is not counteracted.
Cloud whitening proposes the pumping of sea water and then spraying it into the air to increase the number of droplets and production of sea salt crystals that would reflect sunlight. Latham, reported that 1500 spray vessels can produce a negative effect of -37Wm-1 of which had a local cooling effect. Ming et al, (2014) suggests that global cooling effect can be accomplished by meaningful amount of tankers and fleet of commercial vessels equipped to vaporise small droplets of salted water. To have any global effect, is has to be done at a large scale.
Though these methods could reduce some significant effects of global warming and lessen its impact, they may have unforeseen harmful side effects. If there are halogenated compounds in the stratosphere the sulphate aerosols can damage the ozone layer (Ming et al, 2014), the sulphate aerosols may also cause acidic rain. There is also a fear that the orbiting debris may damage the satellites in orbit. Moreover, the solar radiating management do not eliminate the cause of global warming and the threat of ocean acidification.
Rather than reversing global warming, solar radiating management methods reduce the effects of global warming. All these methods are aimed at reducing atmospheric temperatures. To effectively reverse global warming, methods aimed at removing carbon dioxide which is the major cause of the greenhouse effect have to be deviced and carbon emission has to be stopped
, though it may take years.