At a glance - What is the net feedback of clouds?

On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added "At a glance" section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a "bump" for our ask. This week features "What is the net feedback of clouds?". More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.

Fact Myth Cloud

At a glance

What part do clouds play in your life? You might not think about that consciously, but without clouds, Earth's land masses would all be lifeless deserts. Fortunately, the laws of physics prevent such things from being the case. Clouds play that vital role of transporting water from the oceans to land. And there's plenty of them: NASA estimates that around two-thirds of the planet has cloud cover.

Clouds form when water vapour condenses and coalesces around tiny particles called aerosols. Aerosols come in many forms: common examples include dust, smoke and sulphuric acid. At low altitudes, clouds consist of minute water droplets, but high clouds form from ice crystals. Low and high clouds have different roles in regulating Earth's climate. How?

If you've ever been in the position to look down upon low cloud-tops, perhaps from a plane or a mountain-top, you'll have noticed they are a brilliant white. That whiteness is sunlight being reflected off them. In being reflected, that sunlight cannot reach Earth's surface - which is why the temperature falls when clouds roll in to replace blue skies. Under a continuous low cloud-deck, only around 30-60% of the sunlight is getting through. Low clouds literally provide a sunshade.

Not all clouds are such good sunshades. Wispy high clouds are poor reflectors of sunlight but they are very effective traps for heat coming up from below, so their net effect is to aid and abet global warming.

Cloud formation processes often take place on a localised scale. That means their detailed study involves much higher-resolution modelling than the larger-scale global climate models. Fourteen years on, since Ken Gregory of the dubiously-named Big Oil part-funded Canadian group, 'Friends of Science', opined on the matter (see myth box), big advances have been made in such modelling. Today, we far better understand the net effects of clouds in Earth's changing climate system. Confidence is now growing that changes to clouds are likely to amplify, rather than offset, human-caused global warming in the future.

Two important processes have been detected through observation and simulation of cloud behaviour in a warming world. Firstly, just like wildlife, low clouds are migrating polewards as the planet heats up. Why is that bad news? Because the subtropical and tropical regions receive the lion's share of sunshine on Earth. So less cloud in these areas means a lot more energy getting through to the surface. Secondly, we are detecting an increase in the height of the highest cloud-tops at all latitudes. That maintains their efficiency at trapping the heat coming up from below.

There's another effect we need to consider too. Our aerosol emissions have gone up massively since pre-Industrial times. This has caused cloud droplets to become both smaller and more numerous, making them even better reflectors of sunlight. Aerosols released by human activities have therefore had a cooling effect, acting as a counter-balance to a significant portion of the warming caused by greenhouse gas emissions.

But industrial aerosols are also pollutants that adversely affect human health. Having realised this, we are reducing such emissions. That in turn is lowering the reflectivity of low cloud-tops, reducing their cooling effect and therefore amplifying global warming due to rising levels of greenhouse gases.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!


Click for Further details

In case you'd like to explore more of our recently updated rebuttals, here are the links to all of them:

Myths with link to rebuttal Short URLs
Ice age predicted in the 1970s sks.to/1970s
It hasn't warmed since 1998 sks.to/1998
Antarctica is gaining ice sks.to/antarctica
CRU emails suggest conspiracy sks.to/climategate
What evidence is there for the hockey stick sks.to/hockey
CO2 lags temperature sks.to/lag
Climate's changed before sks.to/past
It's the sun sks.to/sun
Temperature records are unreliable sks.to/temp
The greenhouse effect and the 2nd law of thermodynamics sks.to/thermo
We're heading into an ice age sks.to/iceage
Positives and negatives of global warming sks.to/impacts
Global cooling - Is global warming still happening? sks.to/cooling
How reliable are climate models? sks.to/model
Can animals and plants adapt to global warming? sks.to/species
What's the link between cosmic rays and climate change? sks.to/cosmic
Is Al Gore's An Inconvenient Truth accurate? sks.to/gore
Are glaciers growing or retreating? sks.to/glacier
Ocean acidification: global warming's evil twin sks.to/acid
The human fingerprint in global warming sks.to/agw
Empirical evidence that humans are causing global warming sks.to/evidence
How do we know more CO2 is causing warming? sks.to/greenhouse
Explaining how the water vapor greenhouse effect works sks.to/vapor
The tricks employed by the flawed OISM Petition Project to cast doubt on the scientific consensus on climate change sks.to/OISM
Is extreme weather caused by global warming? sks.to/extreme
How substances in trace amounts can cause large effects sks.to/trace
How much is sea level rising? sks.to/sealevel
Is CO2 a pollutant? sks.to/pollutant
Does cold weather disprove global warming? sks.to/cold
Do volcanoes emit more CO2 than humans? sks.to/volcano
How do human CO2 emissions compare to natural CO2 emissions? sks.to/co2
Climate scientists could make more money in other careers sks.to/money
How reliable are CO2 measurements? sks.to/co2data
Do high levels of CO2 in the past contradict the warming effect of CO2? sks.to/pastco2
What is the net feedback of clouds? sks.to/cloud

 

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Posted by John Mason on Tuesday, 24 October, 2023


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