‘Climate scientists dodge the subject of water vapor’–No, they really don’t
(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: Climate scientists never talk about water vapor — the strongest greenhouse gas — because it undermines their CO2 theory.
Answer: Not a single climate model or climate textbook fails to discuss the role water vapor plays in the greenhouse effect. It is the strongest greenhouse gas, contributing 36% to 66% to the overall effect for vapor alone, 66% to 85% when you include clouds. It is however, not considered a climate “forcing,” because the amount of H2O in the air basically varies as a function of temperature.
If you artificially increase the level of H2O in the air, it rains out immediately (in terms of climate response times). Similarly, due to the abundance of ocean on the earth’s surface, if you somehow removed all the water from the air, it would quickly be replaced through evaporation.
This has the interesting consequence that if you could somehow instantly remove all CO2 from the atmosphere, the temperature would begin to drop, causing precipitation to remove H2O from the air, causing even further drops, in a feedback effect that would not end until no liquid water was left, only ice sheets and frozen oceans.
CO2 put into the air by burning fossil fuels, on the other hand, stays in the atmosphere for centuries before natural sinks finish absorbing the excess. This is plenty of time to have substantial and long-lasting effects on the climate system. As the climate warms in response to CO2, humidity rises and increased H2O concentration acts as a significant amplifier of CO2-driven warming, basically doubling or tripling its effect.
An article from RealClimate — “Water vapor: feedback or forcing?” — has a good discussion of this subject.
More stories in this series:
(Part of the How to Talk to a Climate Skeptic guide) Objection: Despite what the computer models tell us, there is actually no evidence of significant global warming. Answer: Global warming is not an output of computer models; it is …
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: CO2 levels are recorded on top of Mauna Loa … a volcano! No wonder the levels are so high. (image courtesty of Global Warming Art)
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: The apparent rise of global average temperatures is actually an illusion due to the urbanization of land around weather stations, the Urban Heat Island effect.
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: One hundred and some years of global surface temperatures is not long enough to draw any conclusions from or worry about anyway. Answer: The reliable instrumental record …
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