Question

although the earth’s atmosphere consists mainly of oxygen and nitrogen, neither plays a significant role in enhancing the greenhouse effect because both are essentially transparent to terrestrial radiation. the greenhouse effect is primarily a function of the concentration of water vapor, carbon dioxide, methane, nitrous oxide, and other trace gases in the atmosphere that absorb terrestrial radiation leaving the surface of the earth. changes in the atmospheric concentrations of these greenhouse gases can alter the balance of energy transfers between the space and the earth systems. the graph above illustrates the amounts and trends of these important greenhouse gases.
because of the connection between greenhouse gases and climate change, there has been a concerted effort to reduce greenhouse gas emissions. the decrease in co₂ emissions in 2015 from fossil fuel combustion was a result of multiple factors. which of the following is not a reasonable factor in this decrease?
a a slight decrease in the use of public transportation during the time period where data was collected.
b substitution from coal to natural gas consumption in the electric power sector.
c a slight decrease in electricity demand due to conservation efforts in all sectors.
d warmer winter conditions resulting in a decreased demand for heating fuel in the residential and commercial sectors.

Explanation:

To determine the unreasonable factor, we analyze each option:

• Option A: A decrease in public transport use would likely increase emissions (as private transport is less efficient), so it’s not a reasonable cause for reduced CO₂ emissions.
• Option B: Substituting coal (high - emission) with natural gas (lower - emission) reduces emissions, so this is reasonable.
• Option C: Reduced electricity demand via conservation lowers emissions from power generation, so this is reasonable.
• Option D: Warmer winters reduce heating fuel demand, lowering emissions from residential/commercial sectors, so this is reasonable.

Answer:

A. a slight decrease in the use of public transportation during the time period where data was collected.