Climate change is one of the most pressing issues of our time, and scientists have long been trying to establish the exact magnitude of the effect human activity has on it. While natural cycles and phenomena also contribute to global warming, research has now reached a consensus that humans are responsible for around a quarter of the global temperature increase since the mid-20th century.
There are several human-generated activities that increase the amount of carbon dioxide and other greenhouse gases in Earth’s atmosphere, with burning fossil fuels at the top of this list. As greenhouse gas emissions from various sources accumulate in the atmosphere, they trap heat inside the Earth and contribute to the global increase in air and ocean temperatures. Deforestation is also a major factor: trees absorb carbon dioxide from the atmosphere and release oxygen, but when they are cut down, their ability to absorb additional carbon is greatly reduced, resulting in higher atmospheric concentrations.
The impact of human activities on global warming is best evaluated by assessing the radiative forcing of the atmosphere, which is the difference between incoming sunlight and outgoing infrared radiation at the Earth’s surface. According to estimates by the Intergovernmental Panel on Climate Change, since 1750 – when humans first began to burn fossil fuels in great quantities – the added radiative forcing of the Earth’s atmosphere has been 1.2 watts per square metre, of which around 75 percent is attributed directly to human activities.
These activities include, but are not limited to, burning of fossil fuels and land use changing, such as urbanization, deforestation and land use changes resulting from industrialization. When stratospheric ozone depleting substances (such as chlorofluorocarbons) are taken into account, the figure rises to almost 85 percent – though the increasing release of ozone-depleting substances are being curbed due to better management of these activities.
That estimated figure of 85 percent rises to 93 percent when the effects of agricultural systems- such as grazing and crop production- that contribute to climate change via emissions of methane and nitrous oxide, are considered. So, with the best estimates from various independent researchers, it is possible to conclude that, overall, humans are responsible for around 93 percent of global warming.
This number changes constantly, though, as more research comes in. Nevertheless, the overwhelming evidence in favour of the part played by human activities on global warming is enough to prompt individuals and governments to take haste in implementing measures to limit carbon emissions. Failure to do so can have catastrophic consequences, both short-term and long-term.
Moreover, initiatives like the Paris Agreement and the development of newer and better technologies can ensure that these targets are met, while a greater awareness of the true environmental costs of human activity as well as ethical considerations can help reduce emissions. Ultimately, only by collectively taking the necessary precautionary measures can we mitigate the devastating effects of global warming caused by human reliance on fossil fuels.
