The amount of water in the air is almost impossible to change because the evaporation and condensation keep the balance "constant". It actually depends on the average temperature and other factors so it's not a real "constant", but unless it's possible to cover all the seas it's impossible to reduce it.

The amount of CO2 changes more slowly, plants and cyanobacteria and some minerals absorb it, but it's a slow process. Natural decomposition, fires and fossil fuel power plants release it, but it's a slow process.

So it's easy to modify the CO2 amount in either direction. Burning fossil fuel to produce energy makes a lot of money. Carbon capture requires a lot of money. So you can guess which one is wining now.

Water vapour is a greenhouse gas but, confusingly, clouds can have either cooling or warming effects. The interactions are pretty complex.

> clouds can have either cooling or warming effects

Just in case anyone is wondering... one of the simplest interactions has to do with daytime and nighttime cloud cover.

Daytime cloud cover causes shade, which _can_ lower temps below the clouds. At night, heat from the ground radiates up and clouds can block the radiated heat. This is why cloudless nights during winter are colder, and cloudy summer nights can be stifling.

The greenhouse coefficient of water vapour is, pound-for-pound, about one hundredth that of CO2.

There's also no meaningful amount of water that can be sequestered, given there's about 10^18 tonnes of it in the world's oceans.

My understanding is it is the other way around, that in equal concentrations water vapor has a much stronger greenhouse effect than carbon dioxide. However for physics reasons the atmosphere does not hold much water vapor.

In fact if I understand correctly this is the mechanism for a runaway greenhouse, that is, something like what happened to venus. Warmer temps allow for more water vapor in the atmosphere, due to it being such a good greenhouse gas, temps then build out of control as more and more water is vaporized.

https://en.wikipedia.org/wiki/Greenhouse_gas#Role_of_water_v...

> However for physics reasons the atmosphere does not hold much water vapor.

The atmosphere is currently ~422 ppm of CO2, and an average of ~5,000 ppm of H2O, with humid tropical areas having up to ~50,000 ppm of H2O.

Water vapour makes up ~half of the greenhouse effect. It's not a 'good' greenhouse gas, it's just that there's a lot of it in the parts of the world that get a lot of sun - the tropics.

I am definitely not an expert on the subject. But doing some basic web searches and I note how much more of the infrared spectra is absorbed by water vs the relatively narrow band that co2 absorbs. As a infrared emission blocking gas water vapor is several times more effective than co2. this is fine, we don't want earth to be a freezing ice cube. but add the excessive amounts of co2 and you start to get an alarming condition.

It may be still more efficient to pump water underground. Isolating CO2 is very energy intensive, for the same amount of energy we may isolate 100x more H2O. Sometimes it even condenses spontaneously!

There is also huge amount of natural CO2, single vulcano eruption... It is about reducing green house gas emissions generated by humans. And there are many artificial lakes, fields and forests that generate huge footprint on water vapour..

Clippy: It looks like you’re trying to turn Earth into Arrakis. Would you like some help with that?

More seriously though, as the effects of climate change intensify, I think it’s all but inevitable we’ll have to seriously look at manipulating whatever environmental factors we can in order to counteract the worst of them. Maybe we can’t do much about the sea level rise, but maybe it would be possible to moderate storm and drought/flooding intensities. As you pointed out, water vapor levels may be one of the easier things we could manipulate, as least on a local or regional scale.

Ignoring all the other problems with that, there is also nearly 100x more water in the atmosphere than carbon dioxide, and roughly 10000x more water in the oceans than the atmosphere. Do you expect sequestering H2O to have a significant impact on the amount in the atmosphere before you dry up the oceans, whence it is evaporating?