Question

methane (ch₄) gas has a five - year global warming potential that is 72 times greater than that of carbon dioxide. the graph shows the changes in global methane concentrations over the past five years.
what can be inferred from the data shown in this graph?
any global warming caused by methane concentrations would be offset by cooling caused by increased carbon dioxide levels.
methane concentrations in the atmosphere have increased by almost 40 ppb, contributing to measurable warming of the atmosphere.
seasonal fluctuations in methane concentrations in the atmosphere indicate that methane has no net effect on global warming.
seasonal fluctuations in the monthly mean methane concentrations are mostly below the adjusted average, contributing to measurable cooling of the atmosphere.

Explanation:

• Analyze each option:
• Option 1: The graph only shows methane data, not carbon dioxide - related cooling, so this is incorrect.
• Option 2: The graph shows an upward trend in methane concentration. If we assume the initial value (around 2012) is about 1800 ppb and the final value (around 2017) is about 1840 ppb, there is an increase of about 40 ppb. And since methane has a high global - warming potential, this increase would contribute to warming.
• Option 3: The fact that there are seasonal fluctuations does not mean methane has no net effect. The overall upward trend (the adjusted average line) shows a net increase which would contribute to warming.
• Option 4: The seasonal fluctuations are around the adjusted average, and the adjusted average is increasing, so it does not contribute to cooling.

Answer:

Methane concentrations in the atmosphere have increased by almost 40 ppb, contributing to measurable warming of the atmosphere.