An article from an authoritative website, not a scientific paper.
Quote:clouds aren’t just poetic; they’re pivotal in helping to regulate Earth’s temperature. And their influence on the climate is evolving in ways we’re only beginning to understand.
How exactly cloud cover will shift in a warming world is anyone’s guess; it’s one of the largest sources of uncertainty in climate science. But it should also be everyone’s concern. What happens to our clouds as the planet warms is so important that we need a renaissance in the study of clouds.
Clouds are classified by their altitude and appearance — whether they look like solid clumps, diffuse layers or wispy streaks. You might remember some of their names from high school:
(diagrams of the different cloud types/elevations)
Quote:These clouds don’t just look different from one another; they also have very different effects on temperatures at the surface of the land or water below. These differences have to do with how much of the sun’s heat they allow through and how much of Earth’s heat they trap in.
Diagrams and text shown.
Quote:Low clouds such as . . . puffy cumulus typically have a cooling effect, as do the clumpy layers known as stratocumulus and the smooth layers known as stratus.
Much of the sun’s rays are reflected off their white tops back up into space. And they are dense enough to cast shadows, cooling the surface below — the natural parasol effect you feel on a beach when one drifts overhead.
Since their water droplets are warmer, they’re as good at radiating Earth’s heat up into space as they are at absorbing it from below. This means they don’t have a pronounced effect of trapping in the warmth below.
Cirrus
High clouds like cirrus and cirrocumulus do the opposite, warming Earth’s surface. Counterintuitively, this is because the ice crystals in these clouds are cold.
These high clouds are often not as dense, and so they can let in more of the sun’s rays.
But since they are cold, they don’t radiate as much of Earth’s heat into space — more like blankets than umbrellas, resulting in a net warming effect.
Getting to the nitty gritty:
Quote:The mix of cloud types over our planet ensures they have an overall cooling effect because the shade from the low clouds outweighs the warming effect of the high ones.
But it’s unclear how clouds will change in a warming climate. With an atmosphere as vast as ours, there is scant empirical data. For now, climate scientists can only make informed guesses, based on ever more sophisticated computer models.
As global temperatures rise, scientists believe we may see fewer of the low, cooling clouds but not of the high, warming ones. It would be a classic feedback loop that accelerates the very warming that triggered it.
In a
paper published in June in Geophysical Research Letters, scientists analyzed 24 years of satellite data on global cloud coverage and how much of the sun’s energy clouds reflect away. It reports a troubling decrease in highly reflective clouds in the regions of our planet where such clouds mostly form: the stormy mid-latitude zones of the Northern and Southern Hemispheres and the tropical stormy regions around the Equator. Cloud cover in these regions appears to be shrinking by about 0.9 percent to 1.3 percent per decade.
In a recent paper in the journal
Science, reduced low cloud cover contributed about 0.2 degrees Celsius, or 0.32 degrees Fahrenheit, to 2023’s record-breaking average global temperatures. In other words, the reduction in Earth’s low clouds helped explain some of the extreme heat that year.
As low cloud cover decreased in recent years, Earth absorbed more heat from the sun [Bold text in article]
Cloud cover decreased because warming allows the atmosphere to carry more moisture but it does not contain as much moisture as it can carry so condensation requires more cooling than before.
Quote:The Intergovernmental Panel on Climate Change has identified climate feedback loops brought on by clouds as one of the largest unknowns in projections of warming. This uncertainty means we can’t say whether the changes we are beginning to observe in clouds are temporary or systemic shifts caused by human-driven climate change. This is why we urgently need greater investment in the study of clouds.
One thing we can do to avoid exacerbating the effect of high clouds is to stop adding to them with aircraft condensation trails, or contrails. When aircrafts fly through humid, cold air at cruising altitude — especially near weather fronts — their exhaust can seed the formation of ice-crystal clouds. When the air at cruising altitude is cool enough and moist enough, these contrails spread into high, thin layers that contribute to atmospheric warming.
It’s entirely possible for airlines to avoid flying at altitudes where the air is conducive to forming contrails. A 2020 study found that adjusting the cruising altitude of just 2 percent of flights could reduce contrail warming by nearly 60 percent, without using much more fuel.
Geoengineering bad:
cont’d
Forum
Pages: 1
Clouds, clouds and global temperature etc (Read 38 times)
