Cloudy feedback on global warming

October 31, 2016, Lawrence Livermore National Laboratory
Lawrence Livermore scientists studied low-level stratocumulus clouds to identify their effects on global warming. Credit: Lawrence Livermore National Laboratory

Lawrence Livermore National Laboratory researchers have identified a mechanism that causes low clouds - and their influence on Earth's energy balance - to respond differently to global warming depending on their spatial pattern.

The results imply that studies relying solely on recent observed trends are likely to underestimate how much Earth will warm due to increased carbon dioxide. The research appears in the Oct. 31 edition of the journal, Nature Geosciences.

The research focused on clouds, which influence Earth's by reflecting incoming solar radiation and reducing outgoing thermal radiation. As the Earth's surface warms, the net radiative effect of clouds also changes, contributing a feedback to the climate system. If these cloud changes enhance the radiative cooling of the Earth, they act as a negative, dampening feedback on warming. Otherwise, they act as a positive, amplifying feedback on warming. The amount of due to increased carbon dioxide is critically dependent on the sign and magnitude of the cloud feedback, making it an area of intense research.

The researchers showed that the strength of the cloud feedback simulated by a climate model exhibits large fluctuations depending on the time period. Despite having a positive cloud feedback in response to long-term projected global warming, the model exhibits a strong negative cloud feedback over the last 30 years. At the heart of this difference are low-level clouds in the tropics, which strongly cool the planet by reflecting solar radiation to space.

"With a combination of climate model simulations and satellite observations, we found that the trend of low-level cloud cover over the last three decades differs substantially from that under long-term global warming" said Chen Zhou, lead author of the paper.

"The key difference is the spatial pattern of global warming", said Mark Zelinka, LLNL climate scientists and co-author of the study. "Not every degree of global warming is created equal, in terms of its effect on low clouds."

In response to increased , climate models predict a nearly uniform warming of the planet that favors reductions in highly reflective and a positive feedback. In contrast, over the last 30 years, tropical surface temperatures have increased in regions where air ascends and decreased where air descends. "This particular pattern of warming is nearly optimal for enhancing low cloud coverage because it increases low-level atmospheric stability that keeps the lower atmosphere moist and cloudy", said Stephen Klein, the third co-author.

"Most satellite data starts around 1980, so linear trends over the last three decades are often used to make inferences about long-term global warming and to estimate climate sensitivity," said LLNL's Chen Zhou, lead author of the study. "Our results indicate that cloud feedback and climate sensitivity calculated from recently observed trends may be underestimated, since the warming pattern during this period is so unique."

Global temperature has gradually increased over the instrumental record due to increased greenhouse gas concentrations. But superimposed on this warming are large temperature fluctuations due to natural internal variability of the climate system, as well as influences from volcanic eruptions, aerosol pollution and solar variability. Whereas warming due to CO2 tends to be relatively spatially uniform, surface temperature trends due to internal climate variability and aerosol pollution are highly non-uniform, with trends on one side of an ocean basin often opposing those on the other. Trends computed over short time periods are often strongly influenced by factors other than CO2 and can be highly misleading indicators of what to expect under CO2-forced global warming.

The team emphasized that clouds are particularly sensitive to subtle differences in surface warming patterns, and researchers must carefully account for such pattern effects when making inferences about cloud feedback and from observations over short time periods.

Explore further: Warning from the past: Future global warming could be even warmer

More information: Chen Zhou et al, Impact of decadal cloud variations on the Earth's energy budget, Nature Geoscience (2016). DOI: 10.1038/ngeo2828

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8 comments

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aksdad
1.3 / 5 (12) Oct 31, 2016
To sum up:

-real-world measurements contradict what the models are predicting
-the real-world measurements must be wrong
-this is our convoluted explanation why the data must be wrong, supported by our models, because we certainly can't trust real-world measurements

Welcome to state-of-the-art climate science in the 21st century.
aksdad
1.3 / 5 (12) Oct 31, 2016
Whereas warming due to CO2 tends to be relatively spatially uniform

Theoretically, yes. Also, theoretically, according to physics, warming due to CO2 should be much less than what the models predict. They arrive at those much higher values by applying arbitrary estimates of "forcings" and "feedbacks" that inflate warming. For example (theoretically), warming causes glaciers to melt which reduces radiation reflected back to space which further amplifies warming. But measured temperatures show the models overestimate warming. See here, from IPCC AR5:

https://www.ipcc....S-14.jpg

Instead of revising the models because their forcings and feedbacks are wrong, climate scientists try to dismiss the validity of the temperature data. A real scientist examines the results of experiments and modifies the theory if they don't agree. Real scientists or witch doctors. I report, you decide.
howhot3
5 / 5 (5) Oct 31, 2016
From the article:
Trends computed over short time periods are often strongly influenced by factors other than CO2 and can be highly misleading indicators of what to expect under CO2-forced global warming.
Thus you lame-O deniers toss a snowball around in the Senate while it's 80 degrees outside and claim, "There is your proof that climate change is non-sense".

Here is the bottom line for the denier goon squad: If it smells like a rotting fish, looks like a rotting fish, who cares what it is, it's something rotting, throw it out. In other words, the climate deniers just need to accept the fact they are wrong, it's not an us vs them issue, its just events beyond them and their cause to control.


Jayded
5 / 5 (7) Nov 01, 2016
@askdad - yeah, knew I was hallucinating all the direct visible effects of increases in energy in the system. must be a hoax am i right? those glaciers are self destructing due to depression.
HeloMenelo
3 / 5 (4) Nov 01, 2016
To sum up:

-real-world measurements contradict what the models are predicting
-the real-world measurements must be wrong
-this is our convoluted explanation why the data must be wrong, supported by our models, because we certainly can't trust real-world measurements

Welcome to state-of-the-art climate science in the 21st century.

To sum it up:

-You are an antigoracle/obama socks/waterprophet/cantdrive/shootist puppet sock goon.

-The evidence provided for global climate change is not only too much for you to read, but your inability to understand it's obvious meaning continues to make you and your puppets look beyond ludicrous every day In turn sinking your losing battle even further by the day.

Welcome to antigoracle he,him and himself posting gobbledygook 24/7 on physorg, mommy never get's him away from his pc in the basement.

HeloMenelo
3.7 / 5 (3) Nov 01, 2016
Whereas warming due to CO2 tends to be relatively spatially uniform

Theoretically, yes. Also, theoretically, according to physics, warming due to CO2 should be much less than what the models predict. They arrive at those much higher values by applying arbitrary estimates of "forcings" and "feedbacks" that inflate warming. For example (theoretically), warming causes glaciers to melt which reduces radiation reflected back to space which further amplifies warming. But measured temperatures show the models overestimate warming. See here, from IPCC AR5:

Instead of revising the models because their forcings and feedbacks are wrong, climate scientists try to dismiss the validity of the temperature data. A real scientist examines the results of experiments and modifies the...


did you understand what you just wrote ? rather go ask daddy to explain again ;)
HeloMenelo
4 / 5 (4) Nov 01, 2016
@askdad - yeah, knew I was hallucinating all the direct visible effects of increases in energy in the system. must be a hoax am i right? those glaciers are self destructing due to depression.


Lol Good one Jay, he always fails to ask his daddy why the climate is so strange and to try let his daddy explain what the science really proved.I'd bet he'd even go on to say that if we give the glaciers an asprin, it would feel better. :D
humy
3.7 / 5 (3) Nov 01, 2016
To sum up:

-real-world measurements contradict what the models are predicting
-the real-world measurements must be wrong

That is an obvious lie by anyone with half a brain who bothers to read what this link actually says. This link clearly does NOT say/imply "the real-world measurements must be wrong". I challenge you to point out exactly WHERE the link does that!!! With which quote in what context?

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