Huge private sector investment puts Paris climate target in reach
Are they going to abate water vapour too?
It's Water Vapor, Not the CO²
ACS Climate Science Toolkit | Narratives
Remark: "The Earth has certainly been warming since we have added so much
CO2 to the atmosphere from fossil fuel burning."
Reply: "Forget the CO2. Water vapor is the most important greenhouse gas.
It controls the Earth's temperature."
It's true, that water vapor is the largest contributor to the Earth's
greenhouse effect. On average, it probably accounts for about 60% of the
warming effect. However, water vapor does not control the Earth's
temperature, but it, is instead, controlled by the temperature. This is
because the temperature of the surrounding atmosphere limits the maximum
amount of water vapor the atmosphere can contain. If a volume of air
contains its maximum amount of water vapor and the temperature is
decreased, some of the water vapor will condense to form liquid water.
This is why clouds form as warm air containing water vapor rises and cools
at higher altitudes where the water condenses to the tiny droplets that
make up clouds.
The greenhouse effect that has maintained the Earth's temperature at a
level warm enough for human civilization to develop over the past several
millennia is controlled by non-condensable gases, mainly carbon dioxide,
CO2, with smaller contributions from methane, CH4, nitrous oxide, N2O, and
ozone, O3. Since the middle of the 20th century, small amounts of man-made
gases, mostly chlorine- and fluorine-containing solvents and refrigerants,
have been added to the mix. Because these gases are not condensable at
atmospheric temperatures and pressures, the atmosphere can pack in much
more of these gases . Thus, CO2 (as well as CH4, N2O, and O3) has been
building up in the atmosphere since the Industrial Revolution when we
began burning large amounts of fossil fuel.
If there had been no increase in the amounts of non-condensable greenhouse
gases, the amount of water vapor in the atmosphere would not have changed
with all other variables remaining the same. The addition of the non-
condensable gases causes the temperature to increase and this leads to an
increase in water vapor that further increases the temperature. This is an
example of a positive feedback effect. The warming due to increasing non-
condensable gases causes more water vapor to enter the atmosphere, which
adds to the effect of the non-condensables.
There is also a possibility that adding more water vapor to the atmosphere
could produce a negative feedback effect. This could happen if more water
vapor leads to more cloud formation. Clouds reflect sunlight and reduce
the amount of energy that reaches the Earth's surface to warm it. If the
amount of solar warming decreases, then the temperature of the Earth would
decrease. In that case, the effect of adding more water vapor would be
cooling rather than warming. But cloud cover does mean more condensed
water in the atmosphere, making for a stronger greenhouse effect than non-
condensed water vapor alone - it is warmer on a cloudy winter day than on
a clear one. Thus the possible positive and negative feedbacks associated
with increased water vapor and cloud formation can cancel one another out
and complicate matters. The actual balance between them is an active area
of climate science research.