Water vapor and carbon dioxide (CO2)
both contribute to the greenhouse effect,
but CO2 has an important influence
on climate change
because CO2 stays in the
atmosphere for a long time.
If we were to magically double
just the amount of water vapor in the atmosphere,
in roughly two weeks
the excess water would rain and snow
back into oceans, ice sheets, rivers,
lakes, and groundwater.
Because water vapor leaves the atmosphere so quickly,
extra vapor doesn’t have
much of a long-term warming effect.
But
if we were to instantly increase
the concentration of CO2,
it would take roughly 100 years
for about half of it to cycle
back into plants and the ocean.
The other half?
Thousands of years.
This is why long-lived greenhouse gases
like carbon dioxide
have an important influence
on Earth’s climate.