Do we see a chicken and egg conundrum when reading that there’s ‘a project to study how low clouds respond to climate change’? Accurate data on clouds in general is sparse, making any assertions about future climate questionable.
– – –
One of the biggest weaknesses in computer climate models – the very models whose predictions underlie proposed political action on human CO2 emissions – is the representation of clouds and their response to global warming.
The deficiencies in computer simulations of clouds are acknowledged even by climate modelers, says Science under attack (via The GWPF).
Yet cloud behavior is key to whether future warming is a serious problem or not.
Uncertainty about clouds is why there’s such a wide range of future global temperatures predicted by computer models, once CO2 reaches twice its 1850 level: from a relatively mild 1.5 degrees Celsius (2.7 degrees Fahrenheit) to an alarming 4.5 degrees Celsius (8.1 degrees Fahrenheit). Current warming, according to NASA, is close to 1 degree Celsius (1.8 degrees Fahrenheit).
Clouds can both cool and warm the planet. Low-level clouds such as cumulus and stratus clouds are thick enough to reflect 30-60% of the sun’s radiation that strikes them back into space, so they act like a parasol and cool the earth’s surface.
High-level clouds such as cirrus clouds, on the other hand, are thinner and allow most of the sun’s radiation to penetrate, but also act as a blanket preventing the escape of reradiated heat to space and thus warm the earth.
Warming can result from either a reduction in low clouds, or an increase in high clouds, or both.
Our inability to model clouds satisfactorily is partly because we just don’t know much about their inner workings either during a cloud’s formation, or when it rains, or when a cloud is absorbing or radiating heat. So a lot of adjustable parameters are needed to describe them.
It’s partly also because actual clouds are much smaller than the minimum grid scale in supercomputers, by as much as several hundred or even a thousand times. For that reason, clouds are represented in computer models by average values of size, altitude, number and geographic location.
Most climate models predict that low cloud cover will decrease as the planet heats up, but this is by no means certain and meaningful observational evidence for clouds is sparse.
To remedy the shortcoming, a researcher at Columbia University’s Earth Institutehas embarked on a project to study how low clouds respond to climate change, especially in the tropics which receive the most sunlight and where low clouds are extensive.
via Tallbloke’s Talkshop
November 4, 2020 at 03:18AM