According to the IPCC's AR5, what is the global warming potential of methane (CH4) over a century?

The global warming potential (GWP) is a measure used to compare the ability of different greenhouse gases to trap heat in the atmosphere over a specified time period, usually 100 years. According to the Intergovernmental Panel on Climate Change's Fifth Assessment Report (AR5), methane (CH4) has a GWP of 28. This means that over a century, one ton of methane has the same warming effect as 28 tons of carbon dioxide (CO2).

This value is significant because methane is a potent greenhouse gas that, despite being less abundant in the atmosphere than CO2, has a much stronger short-term warming effect. The higher GWP of methane emphasizes the importance of addressing its emissions in efforts to combat climate change. By understanding its impact, policymakers and environmental organizations can develop more effective strategies to reduce methane emissions, thereby contributing to climate mitigation efforts.

The other values provided do not accurately reflect the GWP of methane as stated in the IPCC's AR5, making the correct answer clear in the context of climate science and greenhouse gas emissions.