NOAA’s latest offering on this topic is here. Of course we’re pitched into the world of ‘greenhouse gas’ theory. But it seems to be a world of considerable uncertainty, if the phrases highlighted (by the Talkshop) are anything to go by. Most attention is given to CO2 in the media, but it’s only a very minor player in the atmosphere (0.04%). There’s no accepted figure for ‘water vapor’ (NOAA uses US spelling) as exact data doesn’t exist, although ballpark estimates from various readings can be found. Why do greenhouse gas believers obsess about CO2 when they don’t know a lot about what’s going on with water vapor, which is on the face of it far more important to their theory?
Water Vapor is the most abundant greenhouse gas in the atmosphere, which is why it is addressed here first. However, changes in its concentration is also considered to be a result of climate feedbacks related to the warming of the atmosphere rather than a direct result of industrialization.
The feedback loop in which water is involved is critically important to projecting future climate change, but as yet is still fairly poorly measured and understood.
As the temperature of the atmosphere rises, more water is evaporated from ground storage (rivers, oceans, reservoirs, soil). Because the air is warmer, the absolute humidity can be higher (in essence, the air is able to ‘hold’ more water when it’s warmer), leading to more water vapor in the atmosphere.
As a greenhouse gas, the higher concentration of water vapor is then able to absorb more thermal IR energy radiated from the Earth, thus further warming the atmosphere. The warmer atmosphere can then hold more water vapor and so on and so on. This is referred to as a ‘positive feedback loop’.
However, huge scientific uncertainty exists in defining the extent and importance of this feedback loop. As water vapor increases in the atmosphere, more of it will eventually also condense into clouds, which are more able to reflect incoming solar radiation (thus allowing less energy to reach the Earth’s surface and heat it up).
The future monitoring of atmospheric processes involving water vapor will be critical to fully understand the feedbacks in the climate system leading to global climate change. As yet, though the basics of the hydrological cycle are fairly well understood, we have very little comprehension of the complexity of the feedback loops.
Also, while we have good atmospheric measurements of other key greenhouse gases such as carbon dioxide and methane, we have poor measurements of global water vapor, so it is not certain by how much atmospheric concentrations have risen in recent decades or centuries, though satellite measurements, combined with balloon data and some in-situ ground measurements indicate generally positive trends in global water vapor.
via Tallbloke’s Talkshop
July 22, 2019 at 12:10PM