You’ve got questions, and we have answers. No question is too simple or complex for our panel of science advisors who stand ready to field your questions about climate change.
Nadir Jeevanjee, a climate scientist in Princeton University’s Program in Atmospheric and Oceanic Sciences, joins us to answer the following question. Nadir has a background in theoretical physics and currently studies clouds and radiation in the climate system. He is active in communicating climate science to non-specialists and to the public, both through his own talks as well as through the outreach group Climate Up Close. He now works for NOAA’S Geophysical Fluid Dynamics Laboratory, a major US climate modeling center.
Read other Q&A here, and don’t be shy about asking your questions here.
Q: Assuming (big assumption!) we will crack the code to economical green hydrogen production, and with awareness that water vapor does retain heat, wouldn’t the H20 vapor or evaporative by-product of its use in engines and fuel cells still cause global warming? If not, would it contribute to more atmospheric H2O, leading to even more intense precipitation events?
“White” hydrogen (also called natural hydrogen) is mined gas. That would add “new” water, correct? Does that also bear on the questions above?
A: While it is most certainly true that water vapor is a greenhouse gas, unlike CO2 it is very difficult for human activity to alter the amount of water vapor in the atmosphere.
The amount of water vapor (or humidity) at any point in the atmosphere is determined by a competition between processes that moisten the atmosphere, such as evaporation off the ocean surface, and processes that dry the atmosphere, such as the formation and subsequent fallout of raindrops in a thunderstorm.
Humid air, such as the surface air near the U.S. Gulf Coast, for example, has just been moistened by evaporation offshore. Dry air at high altitudes (think about a dry mountaintop) has lost its water through condensation and precipitation as the air made its way to altitude, likely through a thunderstorm or other weather event. Dry air at the surface (such as over the Sahara Desert) is really dry air from on high that has sunk back down to the surface and hasn’t yet been exposed to a moist surface.
So, it is the internal dynamics of the atmosphere (coupled to the ocean surface) that determine atmospheric humidity. Note that the depth of the ocean, or the total amount of water on Earth, doesn’t really play a role in these dynamics, so adding “new” water wouldn’t have much of an effect. If we artificially add water to the atmosphere by burning mined hydrogen, it would temporarily make the atmosphere more humid, but only until the processes that dry the atmosphere bring the humidity back to its original state. The new water would then simply replace water that would otherwise have evaporated off the ocean surface. This would have the effect of very slightly raising sea level, but there would otherwise be no long-term effect on water vapor in the atmosphere or the greenhouse effect.
For further reading, this study quantifies the magnitude of the short-term impacts of such “water-vapor emissions.”
