Which of the following gases currently contributes the maximum overall effect to the phenomenon of global warming among the options given?

Introduction / Context:
Global warming refers to the long term increase in the average temperature of the Earth atmosphere due to enhanced Green House Effect. Several greenhouse gases trap outgoing infrared radiation, but their contributions differ depending on both their warming potential and their concentration in the atmosphere. This question asks which gas among the given options contributes the maximum overall effect to global warming under present conditions.

Given Data / Assumptions:

• The options are methane, chlorofluorocarbon (CFC), nitrogen dioxide, and carbon dioxide.
• We consider both radiative forcing potential and the actual atmospheric concentration of these gases.
• The question is framed at typical examination level that identifies carbon dioxide as the main contributor.

Concept / Approach:
Although some gases like CFCs and methane have a higher global warming potential per molecule than carbon dioxide, their atmospheric concentrations are much lower. Carbon dioxide, on the other hand, is present in much larger quantities and is continuously added by human activities such as burning fossil fuels and deforestation. As a result, carbon dioxide is responsible for the highest overall radiative forcing among greenhouse gases, making it the main driver of anthropogenic global warming in standard exam explanations.

Step-by-Step Solution:
Step 1: Recognise that methane is a strong greenhouse gas with a higher warming potential per molecule than carbon dioxide, but its concentration in the atmosphere is significantly lower. Step 2: CFCs are also very powerful greenhouse gases and contribute to ozone layer depletion, yet their concentrations are controlled by international agreements and are comparatively small. Step 3: Nitrogen dioxide is mainly discussed in the context of air pollution and acid rain rather than as the dominant greenhouse gas. Step 4: Carbon dioxide is produced in huge quantities by combustion of coal, oil, and natural gas, as well as by deforestation, and it accumulates in the atmosphere over long periods. Step 5: Therefore, carbon dioxide is recognised as the gas that contributes the maximum overall effect to global warming among the listed gases.

Verification / Alternative check:
Reports on climate science and standard environmental textbooks emphasise that most of the increase in radiative forcing over the last century is due to rising carbon dioxide levels. Graphs of greenhouse gas contributions consistently show carbon dioxide as the largest component of human induced forcing, with methane and other gases providing smaller but still important shares. This repeated emphasis confirms that, in examination contexts, carbon dioxide is considered the leading gas responsible for global warming.

Why Other Options Are Wrong:

• Methane: Has a higher warming potential per molecule, but its lower concentration means its total effect is less than that of carbon dioxide in most standard assessments.
• Chlorofluorocarbon (CFC): Very strong greenhouse gases, but present at low concentrations and mainly discussed in relation to ozone depletion.
• Nitrogen dioxide: Important for smog formation and acid rain but is not identified as the main driver of global warming.

Common Pitfalls:
One common pitfall is focusing only on global warming potential values without considering atmospheric abundance. This leads some learners to choose methane or CFCs. Another mistake is to confuse gases most responsible for ozone layer depletion with those that drive global warming. To avoid these errors, remember that carbon dioxide is both abundant and long lived, making it the principal greenhouse gas behind current climate change in typical exam contexts.

Final Answer:
The gas that contributes the maximum overall effect to global warming among the options listed is carbon dioxide.