Superfact 133: Water vapor is responsible for roughly half of Earth’s total greenhouse effect, but unlike carbon dioxide or methane, water vapor condenses and falls as precipitation. Water molecules only stay in the atmosphere for about two weeks. We do not directly control global water vapor levels. When carbon dioxide warms the planet the atmosphere holds more water vapor, which amplifies the initial warming. However, water vapor does not drive global warming. Carbon dioxide emissions and to a lesser degree methane emissions drive global warming. Water vapor just amplifies the effect.
On social media you often see the claim that water vapor is a more powerful greenhouse gas than carbon dioxide, and the implicit implication is supposedly that our carbon emissions are not the problem. Alternatively, since water vapor has been around forever and is a more powerful greenhouse gas than carbon dioxide, global warming can’t be caused by greenhouse gases. What is getting lost in these posts is that we are not adding water vapor to the atmosphere like we are adding carbon dioxide (or methane) to the atmosphere. The amount of water vapor in the atmosphere will increase because a warmer atmosphere can hold more water vapor, but that is because of our carbon emissions in the first place. You can read more about that here, and here, and here.
A related fact is that the water cycle is a relatively fast cycle compared to the carbon cycle. A water molecule stays in the atmosphere on average for two weeks according to MIT and nine days according to Wikipedia. Our carbon emissions stay in the atmosphere for several hundred years. In short, water vapor is not the driver of the current rapid global warming. That is chiefly carbon dioxide, but also methane, and deforestation.
It does not matter that water vapor causes a larger percentage of the warming than carbon dioxide. It is not what is causing the increase in the average global temperature. Since so many people have been fooled by the water vapor misdirection, incorrectly thinking that carbon dioxide is unimportant because water vapor is a more important greenhouse gas, this is an important fact that will come as a surprise to many. Therefore, it is a super fact in my opinion.
More on the Water Cycle and the Greenhouse Effect
Below is a more detailed illustration of the water cycle for those who are interested. It should be noted that even though water vapor is not driving the rapid global warming we are witnessing, the very rapid global warming we are experiencing is affecting the water cycle, for example, the precipitation patterns around the world. You can read more about that here.
Another less simplistic argument based on water vapor as a greenhouse gas that tries to claim that carbon dioxide is not behind the rapid global warming we are seeing is that water vapor is such an effective greenhouse gas across all frequences that there is not much room for carbon dioxide to make it worse.
Greenhouse gases absorb infrared radiation and that is what warms the atmosphere like a blanket. However, the different greenhouse gases absorb radiation at different frequencies. As you can see in the figure below water vapor has a pretty impressive spread across most frequencies.
However, if you look carefully, you see that carbon dioxide and water vapor complement each other in the spectra and in addition, as mentioned, we are not increasing water vapor directly, but we are increasing the amount of carbon dioxide directly. It should be noted that, in addition, satellite measurements directly confirm that our emissions are warming the planet. The topic of absorption at different frequencies by carbon dioxide and water vapor is explored in greater detail in the book “The Physics of Climate Change by Lawrence M. Krauss”, which I reviewed here.
Conclusion
Water vapor is a powerful greenhouse gas but unlike carbon dioxide and methane it is not driving the rapid global warming that we are seeing. We are directly increasing water vapor via water vapor emissions, and if we did it would just come raining back down pretty quickly. However, when carbon dioxide warms the planet the atmosphere holds more water vapor, which amplifies the initial warming.
Other super facts related to global warming
- Global Warming is Happening and is Caused by us
- The Hockey Stick Graph is not Wrong
- Scientists Agree that Global Warming is happening and that we are the Cause
- Climate change worsens wildfires in the US
- Without carbon dioxide the Earth would freeze
- IPCC Did Not Backtrack on Global Warming Being Human Caused
- Orbital Cycles are not the Cause of the current Global Warming
- The Sun is not the Cause of the current Global Warming
- Volcanoes emit a tiny fraction of carbon compared to humans
- Climate change worsens wildfires Globally and human Land-Use Changes Reduces them
- Carbon Cycle Emissions Does Not Cause Global Warming
To see the other Super Facts click here
Yes. Thank you.
We are killing life on our planet aggresively. But species extinction is repetitive and old on earth.
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That might be true, but it is not morally right to just accept species extinction as a sad fact of life when said extinction is caused by deliberate human activity.
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Yes Alex, you are right of course. Mass extinctions have happened on average every 100 million years. Humans have been around 200,000 years and civilization 10,000 years and modern industrial civilization 150-200 years. Those latter time periods are just tiny blips. Being a tiny blip that causes a mass exctinction is not something to be proud of.
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Yes you are right. The extinction rate is thousands of times faster than normal but mass extinctions have happened before, about every 100 million years. A mass exctinction is defined as when more than 75% of all species die out within two million years, and it looked like we were way ahead of the curve for a while, to put it that way. However, it seems like we have been doing better lately. Maybe we won’t cause the fastest mass excinction in earth’s history after all. The current rapid climate change / global warming could cause a lot of problems though.
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Charles Koch, one of the wealthiest men and a staunch conservative in the United States, spends millions of dollars to fund climate change denialism, and to make sure the federal government doesn’t fund any scientific research on the effects of human activity on the planet’s climate.
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Yes I am aware of this Alex. It is sad. The Koch brother’s have caused immense damage to our children and grand children.
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I hadn’t heard that climate change deniers blame water. Anything except the main cause I guess. Maggie
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I think “Anything except the main cause..” is a great way to put it. I should add that the water vapor argument also comes in form of “greenhouse gases can’t be the problem since water vapor has been around for ever”. I should clarify that. But in any case, the argument leaves out the most important truth regarding water vapor as a greenhouse gas, and that is that it is not directly added to the atmosphere by us. Anyway, I’ve never seen this argument in my native country Sweden, but I see and hear it here in Texas where I live now, and I see it on social media. I think it depends on where you live and who you hang around, but I’ve seen it many times.
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I love the charts and your amazing knowledge on the subject, Thomas! You always share amazing posts to learn from Thomas! There is so much science here to confirm your findings and we have to get to the corporations that create more hazards and do our part. Great post! xx
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Thank you so much for your very kind words Cindy. I really appreciate it.
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You’re so welcome, Thomas! They’re so deserved!!! 💕🙏💕
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Thank you so much Cindy
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-:) xx
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Thank you for another good post exploring the science behind global warming. Indeed, it’s important to understand the reason there’s more water in the atmosphere now than in the past. As my graduate advisor used to say, the most important question a scientist can ask is “why?”
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Thank you so much for your kind words David. And your graduate advisor sounds wise.
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An excellent post, Thomas. I did like those diagrams, and I definitely remember the first one, the simple water cycle. I am sure I drew it in geography when I was at school!
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Thank you so much Chris and it is very cool that you drew the water cycle in geography. That is a great one to remember.
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Hi Thomas, to be honest the deliberate manipulation of information to mislead the masses about climate change is completely depressing. Humanity should be uniting to fight this huge and fast approaching train wreck. Instead the officials we elect to lead us in the right direction mislead for personal gain. Most are old men who will not live to reap what they are sowing. The complete disregard for all life, including human life, on this planet is incomprehensible to me.
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Yes the deliberate manipulation of information to mislead the masses about climate change is depressing. The fossil fuel industry put billions of dollars into it and even though they mostly stopped now, politicians are doing it all the time. It lives on. If we all could just be a little bit less gullible. Well I am speaking to myself here too, because I was bamboozled too. It was my own fault. I was only reading right-wing news, not trying to understand it. When I did, it all changed. On the other hand this problem with misinformation gives me a lot of opportunities for super facts. I can surprise a lot of people with facts they’ve misunderstood. Well it is a pretty small silver lining.
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Hi Thomas, these super facts posts are great and you are reaching people. The posts are out there and get hits by interested people. I do this with my animal posts. It’s something.
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Lulu: “… and boy howdy has the atmosphere been returning that extra water vapor to us in spades lately!”
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Yes it does that in some places. You are right Lulu. When the atmosphere holds more water vapor you tend to get more rain. It especially happens with hurricanes that get rainier with more floods. But not here in north Texas though. 95 degrees today and no rain for a really long time. But we may get some soon.
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I like how you organize these posts with the superfact stated first and a conclusion at the end so that if I don’t have time to read the whole post, I can get the gist of it.
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Thank you so much JoAnna. Yes that is exactly the idea. A short summary in bold, and that is all you need to know, unless you want to dispute it, then you should read the whole thing.
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