Where the atmosphere is cooler, water vapour condenses into tiny droplets of water known as clouds (fog at ground level) which may coalesce into rain, ice pellets (hail) or snow.
Water vapour represents up to 90 % of greenhouse gas volume in the atmosphere. Water in the form of snow and ice also reflects the sun's radiation back into space while also acting as an insulating blanket to reduce heat loss from the ground, and from water underneath a layer of ice and snow. This permits the Ottawa river (which supplies water to the City of Ottawa, Canada) to flow throughout the winter when daytime temperatures are routinely between minus 10 and minus 20 degrees Celsius (C). (Fresh water freezes at zero degrees C).
The Earth's seas and oceans and atmospheric water vapour, provide the planet with considerable thermal inertia; which is why most of the planet does not freeze over at night.
Clouds act like a blanket to prevent heat from the ground radiating back into space, This also explains temperature variations between night and day, in very dry (cloudless) desert areas, which can be more than 30°C (54°F).Conversely, clouds also act as a sun shield by reflecting up to 90% of solar radiation back into space.
Steve Koonin (Under Secretary for Science at the U.S. Department of Energy from 2009 to 2011) pointed this out in his book, "Unsettled", noting that a 5 percent increase in cloud cover can largely offset a temperature increase caused by doubling atmospheric carbon dioxide (CO2).
He also noted that the Intergovernmental Panel on Climate Change (IPCC) computer models could not explain the past century's climate variations.
John Clauser, a recipient of the 2022 Nobel Prize in Physics, also challenged the accuracy of prevailing climate models, pointing out that they overemphasize the impact of greenhouse gases like carbon dioxide (CO2) while ignoring the fact that clouds reflect up to 90% of solar radiation back into space.(Thick cloud cover can reduce solar panel output by up to 90% compared to full sunlight. Thinner cloud cover causes a less severe reduction).
Satellite images consistently show wide variances in cloud cover, which can cover from five to 95 percent of the Earth's surface.
A photos from NASA's Earth Polychromatic Imaging Camera on the DSCOVR satellite on Sept. 11, 2018.
https://epic.gsfc.nasa.gov/science/products/vis
John Clauser also points out that clouds serve as a natural thermostat that stabilizes the Earth's temperature. As two-thirds of the Earth surface is covered by oceans, minimal clouds increases exposure to solar radiation causing increased evaporation and cloud formation. Conversely, extensive cloud cover reflects more solar radiation back into space. Thereby reducing evaporation and cloud formation.
This thermostat mechanism has a greater influence on Earth's temperature than the effect of greenhouse gases like CO2 or methane. Preliminary calculations suggest that the impact of this cloud-reflectivity thermostat might exceed CO2's influence by more than 100 times.
Clouds tend to have a cooling effect by reflecting solar radiation back into space, while low thick clouds have a warming effect by trapping some of the Earth's outgoing long-wave radiation.
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