Casting a Dry Spell

The relative lifetimes of CO2 and aerosol in the atmosphere result in the expectation that reducing fossil fuel use will accelerate warming. A CO2 molecule has a lifetime of about 100 years in the atmosphere, while an aerosol particle has an average life expectancy of only about 10 days. Therefore, if we instantaneously ceased using combustion engines, the (cooling) fossil fuel-related aerosols would be cleaned out of the atmosphere within weeks, while the (warming) CO2 would remain much longer, leaving a net positive forcing from the reduction in emissions for a century or more.

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