Greenhouse effect and climate change – UGC NET Question

Among greenhouse gases emitted by human activities, carbon dioxide contributes the most to anthropogenic global warming in terms of total radiative forcing. It is released mainly from burning fossil fuels, deforestation and industrial processes. Although other gases like methane and nitrous oxide have higher warming potential per molecule, their concentrations and total forcing are lower. Hence, carbon dioxide is regarded as the primary driver of the enhanced greenhouse effect, making option D correct.

Option A:
Option A, nitrous oxide, is a potent greenhouse gas but its atmospheric concentration and total contribution to warming are smaller compared to carbon dioxide. It is significant in agriculture and industry, yet not the largest contributor overall.

Option B:
Option B, methane, has a higher global warming potential than carbon dioxide per unit mass but is present in much lower concentrations. Its total radiative forcing is less than that of carbon dioxide, so it is not the largest contributor to anthropogenic warming.

Option C:
Option C, chlorofluorocarbons, are powerful greenhouse gases and ozone-depleting substances, but due to regulation under the Montreal Protocol, their emissions have declined. Their overall contribution is less than that of carbon dioxide.

Option D:
Option D is correct because carbon dioxide is emitted in very large quantities from energy, transport and land-use change. Its long atmospheric lifetime and cumulative build-up make it the major contributor to human-induced climate change.