4 ms·

Is water vapor some kind of greenhouse gas? How does its' infrared absorption measure up to carbon dioxides'?

atoav 3y ago
Afaik it is a strong greenhouse gas, but under normal circumstances the amount of water vapor in the global air is more or less the same so it won't matter that much. Now we don't live in normal circumstances, but in a society that hasn't given economic value to an environment that is essential to it's survival. And so it happens like in France where nuclear energy couldn't be used anymore because there wasn't enough water in the rivers for the process anymore, during a particularly hot summer. Essentially water vapor is one of the runaway feedback loops for cilmate change, more vapor means more greenhouse effect, means warmer, means more vapor, etc. This works until the air is saturated. Climate is driven by a bunch of those complex feedback loops and includes tipping points (e.g. particular big ice structures melting) so predicting how exactly it will pan out isn't trivial. A side effect of more water vapor is also that storms get stronger and rain falls worse.
- shakow 3y ago
  > nuclear energy couldn't be used anymore because there wasn't enough water in the rivers for the process anymore That's a deformation; production had to be reduced (not stopped), not because there was not any water anymore, but because the exhaust water temperature would have been over the threshold for ecosystem stability. The plants could have been run at full power if we were OK with toasting the shellfishes.
perihelions 3y ago
Yes. But there's ten trillion tons of water vapor in the troposphere, so, normally this wouldn't be a relevant amount. It's key that the volcano eruption lifted the water vapor completely outside the weather layer, into the stratosphere. A marginal unit of water in the stratosphere is a lot more potent as a greenhouse gas, than the same unit in the troposphere. (I don't know the quantified values).
KaiserPro 3y ago
It absorbs a lot of the spectrum, both UV and IR. https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water#/media/File:Absorption_spectrum_of_liquid_water.png https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_... However clouds reflect. So high humidity will absorb ir, but thick cloud will reflect. So its a bit more complex.
aeroman 3y ago
Water vapour is a very strong infrared absorber, so much so that it is more important for the greenhouse effect than CO2. However, it is usually very difficult to change the amount of water vapour in the atmosphere as a whole (it just rains out). The stratosphere cycles through much slower than the troposphere (there are very few clouds, for example). That means that if you put water there, it can stay there for a lot longer, increasing the total amount of water in the atmosphere and warming the climate. I'll also say that we expect water vapour to increase as temperature increases, which is a positive feedback in the climate system,increasing the warming beyond that of CO2.this is known as the water vapour feedback.
- perihelions 3y ago
  - "That means that if you put water there, it can stay there for a lot longer" There's more to it than that. Large parts of the water bands in the troposphere are already saturated: adding more and more of the same absorbing material doesn't have a linear effect, but diminishing returns. But the stratosphere is completely dry. The marginal effect of a water unit is a lot greater.
taylodl 3y ago
Water vapor is an extremely powerful greenhouse gas - however, it's presence in the atmosphere is extremely variable and so it's very difficult to measure long-term trends versus just what the weather is doing today. That's why we use CO2 as our climate change marker. CO2 is nowhere near as powerful of a greenhouse gas, but it's stable in the atmosphere for centuries. That makes it easy to track trends, versus today's weather, and you're also tracking a variable that has long-term consequences. For the record, methane is another strong greenhouse gas but like CO2, it's concentration in the atmosphere is highly variable, so we don't tend to track it.

Afaik it is a strong greenhouse gas, but under normal circumstances the amount of water vapor in the global air is more or less the same so it won't matter that much. Now we don't live in normal circumstances, but in a society that hasn't given economic value to an environment that is essential to it's survival. And so it happens like in France where nuclear energy couldn't be used anymore because there wasn't enough water in the rivers for the process anymore, during a particularly hot summer. Essentially water vapor is one of the runaway feedback loops for cilmate change, more vapor means more greenhouse effect, means warmer, means more vapor, etc. This works until the air is saturated. Climate is driven by a bunch of those complex feedback loops and includes tipping points (e.g. particular big ice structures melting) so predicting how exactly it will pan out isn't trivial. A side effect of more water vapor is also that storms get stronger and rain falls worse.

shakow 3y ago
> nuclear energy couldn't be used anymore because there wasn't enough water in the rivers for the process anymore That's a deformation; production had to be reduced (not stopped), not because there was not any water anymore, but because the exhaust water temperature would have been over the threshold for ecosystem stability. The plants could have been run at full power if we were OK with toasting the shellfishes.

perihelions 3y ago

Yes. But there's ten trillion tons of water vapor in the troposphere, so, normally this wouldn't be a relevant amount. It's key that the volcano eruption lifted the water vapor completely outside the weather layer, into the stratosphere. A marginal unit of water in the stratosphere is a lot more potent as a greenhouse gas, than the same unit in the troposphere. (I don't know the quantified values).

KaiserPro 3y ago

It absorbs a lot of the spectrum, both UV and IR. https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water#/media/File:Absorption_spectrum_of_liquid_water.png https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_... However clouds reflect. So high humidity will absorb ir, but thick cloud will reflect. So its a bit more complex.

aeroman 3y ago

Water vapour is a very strong infrared absorber, so much so that it is more important for the greenhouse effect than CO2. However, it is usually very difficult to change the amount of water vapour in the atmosphere as a whole (it just rains out). The stratosphere cycles through much slower than the troposphere (there are very few clouds, for example). That means that if you put water there, it can stay there for a lot longer, increasing the total amount of water in the atmosphere and warming the climate. I'll also say that we expect water vapour to increase as temperature increases, which is a positive feedback in the climate system,increasing the warming beyond that of CO2.this is known as the water vapour feedback.

perihelions 3y ago
- "That means that if you put water there, it can stay there for a lot longer" There's more to it than that. Large parts of the water bands in the troposphere are already saturated: adding more and more of the same absorbing material doesn't have a linear effect, but diminishing returns. But the stratosphere is completely dry. The marginal effect of a water unit is a lot greater.

taylodl 3y ago

Water vapor is an extremely powerful greenhouse gas - however, it's presence in the atmosphere is extremely variable and so it's very difficult to measure long-term trends versus just what the weather is doing today. That's why we use CO2 as our climate change marker. CO2 is nowhere near as powerful of a greenhouse gas, but it's stable in the atmosphere for centuries. That makes it easy to track trends, versus today's weather, and you're also tracking a variable that has long-term consequences. For the record, methane is another strong greenhouse gas but like CO2, it's concentration in the atmosphere is highly variable, so we don't tend to track it.