Spotty coverage: Climate models underestimate cooling effect of daily cloud cycle

Spotty coverage: Climate models underestimate cooling effect of daily cloud cycle
The researchers used both reanalysis data and satellite images from 1986-2005 to calculate the average diurnal cycles of clouds in each season worldwide. The reanalysis (above) shows (left to right) the mean (average), standard deviation (amplitude) and phase (timing) of global cloud coverage by season. The color scale indicates low (blue) to high (red) coverage, amplitude and timing. The majority of models suggest that clouds are thickest over land in the early morning. The Princeton study showed, however, that cloud coverage peaks more frequently in the afternoon. Credit: Jun Yin, Department of Civil and Environmental Engineering

Princeton University researchers have found that the climate models scientists use to project future conditions on our planet underestimate the cooling effect that clouds have on a daily—and even hourly—basis, particularly over land.

The researchers report in the journal Nature Communications Dec. 22 that models tend to factor in too much of the sun's daily heat, which results in warmer, drier conditions than might actually occur. The researchers found that inaccuracies in accounting for the diurnal, or daily, cloud cycle did not seem to invalidate climate projections, but they did increase the margin of error for a crucial tool scientists use to understand how will affect us.

"It's important to get the right result for the right reason," said corresponding author Amilcare Porporato, a professor of civil and and the Princeton Environmental Institute. "These errors can trickle down into other changes, such as projecting fewer and weaker storms. We hope that our results are useful for improving how clouds are modeled, which would improve the calibration of climate models and make the results much more reliable."

Porporato and first author Jun Yin, a postdoctoral research associate in civil and environmental engineering, found that not accurately capturing the daily cloud cycle has the sun bombarding Earth with an extra 1-2 watts of energy per square meter. The increased carbon dioxide in the atmosphere since the start of the Industrial Age is estimated to produce an extra 3.7 watts of energy per square meter. "The error here is half of that, so in that sense it becomes substantial," Porporato said.

Yin and Porporato undertook their study after attending a seminar on cloud coverage and climate sensitivity. "The speaker talked a lot about where the clouds are, but not when," Yin said. "We thought the timing was just as important and we were surprised to find there were fewer studies on that."

Clouds change during the day and from day-to-day. Climate models do a good job of capturing the average cloud coverage, Yin said, but they miss important peaks in actual cloud coverage. These peaks can have a dramatic effect on daily conditions, such as in the early afternoon during the hottest part of the day.

"Climate scientists have the clouds, but they miss the timing," Porporato said. "There's a strong sensitivity between the daily cloud cycle and temperature. It's like a person putting on a blanket at night or using a parasol during the day. If you miss that, it makes a huge difference."

The researchers used satellite images from 1986-2005 to calculate the average diurnal cycles of clouds in each season worldwide. Yin analyzed the cloud coverage at three-hour intervals, looking at more than 6,000 points on the globe measuring 175 miles by 175 miles each.

Yin and Porporato compared the averages they came up with to those from nine climate models used by climate scientists. The majority of models have the thickest coverage occurring in the morning over the land rather than in the early afternoon when clouds shield the Earth from the sun's most intense heat. "A small difference in timing can have a big radiative impact," Yin said.

The researchers plan to explore the effect different types of clouds have on climate-model projections, as well as how cloud cycles influence the year-to-year variation of Earth's temperature, especially in relation to extreme rainfall.

Gabriel Katul, professor of hydrology and micrometeorology at Duke University, said that "the significance is quite high" of accurately modeling the daily cloud cycle. Katul was not involved in the research but is familiar with it.

The cloud cycle can indicate deficiencies in the characterization of surface heating and atmospheric water vapor, both of which are necessary for , he said. Both factors also govern how the lowest portion of Earth's atmosphere—known as the atmospheric boundary layer—interacts with the planet's surface.

"The modeling of boundary-layer growth and collapse is fraught with difficulties because it involves complex processes that must be overly simplified in climate models," Katul said. "So, exploring the timing of cloud formation and cloud thickness is significant at the diurnal scale precisely because those timescales are the most relevant to boundary-layer dynamics and surface-atmosphere heat and water-vapor exchange."

When it comes to clouds, climate models have typically focused on mechanisms, spatial areas and timescales—such as air pollution and microphysics, hundreds of square kilometers, and seasons, respectively—that are larger and more generalized, Katul said. "There are practical reasons why data-model comparisons were conducted in a manner that masked the diurnal variation in clouds," he said. "Diurnal variation was somewhat masked by the fact that much of the climate- performance was reported over longer-term and larger-scale averages."

By capturing the timing and thickness of the daily cloud cycle on a global scale, however, Yin and Porporato have provided scientists with a tool for confirming if models aptly portray cloud formation and the interaction between clouds and the atmosphere.

"The global coverage and emphasis on both 'timing' and 'amount' are notable. As far as I am aware, this is the first study to explore this manifold of models in such a coherent way," Katul said. "I am sure this type of work will offer new perspectives to improve the representation of . I would not be surprised to see this paper highly cited in future IPCC [U.N. Intergovernmental Panel on Climate Change] reports."

The paper, "Diurnal cloud cycle biases in ," was published online Dec. 22 by Nature Communications.


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Journal information: Nature Communications

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Jan 09, 2018
The models keep getting better and more accurate, while computers continue to get more powerful enabling those new and more sophisticated models to be executed on finer and finer grids. It tickles me to see the scientific process continue to hammer at the underlying issues creating continuous improvement and refinement.

Jan 09, 2018
Looking forward to denialists just reading the headline and making their idiocy more obvious.

Jan 10, 2018
Odd PTTG, I was looking forward to what the warmists would say, since all their current climate models have just been invalidated.

""The error here is half of that (estimated CO2 caused increased wattage), so in that sense it becomes substantial," Porporato said.


Jan 10, 2018
Tyrant
since all their current climate models have just been invalidated
Why would you say that? This from the article
The researchers found that inaccuracies in accounting for the diurnal, or daily, cloud cycle did not seem to invalidate climate projections

Jan 10, 2018
'Looking forward to denialists just reading the headline and making their idiocy more obvious.'
Along game Tyrant, right on cue...

Jan 10, 2018
First of all kudos to the researchers for discovering something of real importance.

I have been claiming for years that the models did not reflect cloud cover and water vapor properly. There are still more feedback loops that will be discovered and climate models will not be of mch real use until they are.

Jan 10, 2018
The researchers found that inaccuracies in accounting for the diurnal, or daily, cloud cycle did not seem to invalidate climate projections,
'Nuff said. The #climatedeniers will of course make the usual claims backed with cherry-picked evidence.

Jan 10, 2018
First of all kudos to the researchers for discovering something of real importance.

I have been claiming for years that the models did not reflect cloud cover and water vapor properly. There are still more feedback loops that will be discovered and climate models will not be of mch real use until they are.


The researchers found that inaccuracies in accounting for the diurnal, or daily, cloud cycle did not seem to invalidate climate projections,
'Nuff said. The #climatedeniers will of course make the usual claims backed with cherry-picked evidence.


Yeah, never mind that the current models accurately predicted the real-world impacts we're seeing right now. This will show they were all wrong!

Or, you know, not.

As they said, this is not about model projections but about refining them to more accurately reflect the climate system.

Jan 10, 2018
Good God they were 50% off on the amount of energy reaching the earth yet they claim the models are correct. What they have just proven is that anything predicted by the models that resembles today's climate is purely coincidental!

Jan 10, 2018
"The researchers found that inaccuracies in accounting for the diurnal, or daily, cloud cycle did not seem to invalidate climate projections"

Of course not, no huge error, mistake, or oversight ever invalidates this pseudoscience fantasy.

Jan 10, 2018
"Thanks to the limited responses of DCC (diurnal cloud cycle) to global warming, such biases do not seem to invalidate future climate projection; however, they may induce an overestimation of cloud-feedback strength and distort the patters of land–ocean–atmosphere interaction. Improving resolution and parameterizations of atmospheric convection may help reduce the reliance of model tuning and provide more accurate climate projections."

I did not read all of the paper but, those line above, are the concluding lines of the paper. https://www.natur...-02369-4
So fuck you deniers.

Jan 11, 2018
Good God they were 50% off on the amount of energy reaching the earth
No they were not. They were 50% off in the amount of EXTRA energy reaching the earth. Now put that into context. About 1,000 watts per Meter squared hits the earth at the equator. A lot of that energy is reflected back into space.That amount has been altered by about 3.7 watts according to this article - but that number may be 1 - 2 watts - based on this new research. But clouds only go up to about 20,000 feet (5 miles). The atmosphere is about 300 miles thick. So MR of course thinks he can do the math on the back of a napkin - in terms of how that affects the big picture of the climate. A lot of the energy is reflected back into space - and maybe the extra cloud cover also traps some more of that heat. So there is pluses and minuses. Supreme arrogance on the deniers part.

Jan 11, 2018
Snow falls in the Sahara three years in a row after not doing so for decades. That's called global warming... The Chicken Littles are delusional.

Jan 11, 2018
Some folk who have no appreciable education in science are unaware of how global warming is not just gradual warming, but means more extreme weather as the process gets more energy from evaporating water.

Did can'tdrive see what is happening to the roads in Australia? They are MELTING!

Jan 11, 2018
Did George see the Earth's magnetic field is weakening? Of course this couldn't have any affect on weather or climate...

Jan 11, 2018
Snow falls in the Sahara three years in a row after not doing so for decades. That's called global warming... The Chicken Littles are delusional.
@cd the idiot pseudoscience eu cultist

if you are literate, you can read one of the many links I've sent to you showing you where Francis and Vavrus actually spell it out in monosyllabic explanations easily understood by cults and children alike

or go directly to the study here:
http://iopscience...1/014036

If that is too hard to understand, you can watch the video that explains it here:
https://www.youtu...m9JAdfcs

if that is too hard, I can link some of the other threads where Thermodynamics and runrig explain, in detail, the studies (validated) and why we see cold snaps in global warming


Jan 11, 2018
"Did George see the Earth's magnetic field is weakening? Of course this couldn't have any affect on weather or climate..."

Wow, . . I have to admit I had no idea the weakening of Earth's magnetic field could melt roads in Australia!

Thanks for the education in conservative science, cantdrive85.

Jan 11, 2018
Who'da thunk a weaker magnetic field could allow more energy into the Earth's atmosphere. How could more energy in the system possibly affect weather and climate? Is it any wonder why the Chicken Littles deserve such derision and contempt directed toward them?

Jan 11, 2018
The science is settled.

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