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By Sherry Listgarten

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About this blog: Climate change, despite its outsized impact on the planet, is still an abstract concept to many of us. That needs to change. My hope is that readers of this blog will develop a better understanding of how our climate is evolving a...  (More)

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Clouds of Uncertainty

Uploaded: Feb 9, 2020
Clouds have a cooling effect on the planet. “Yes, and the sky is blue”, you may be thinking. “Isn’t that obvious, and why should we care?” Strangely, it is not obvious that clouds cool the climate, and it’s also not particularly good news. This post will review some of what we know about the impact of clouds on climate, and explain why understanding them better can save us trillions(!) of dollars. (1)

Clouds over the Americas. Source: NASA

Clouds Are Tricky
Clouds appear over about two-thirds of the Earth. They form when pockets of warm air rise into cooler air, where the water vapor condenses around particles like dust, sea salt, or sulfates into cloud droplets. (2) Other mechanisms, such as cooling at the tops of the clouds, help the clouds stay in place once formed.

Clouds have the potential to both cool and warm the Earth. They can cool the Earth because they reflect sunlight. They can warm the Earth because they trap the heat that’s radiating up.

In general, low-lying white cumulus clouds cool the Earth, while thin, high cirrus clouds warm the Earth. Blankets of low, highly reflective stratocumulus clouds critically cover about 20% of our tropical ocean area. According to one estimate, “the net effect of clouds on the climate today is to cool the surface by about 5°C (9°F).”

Stratocumulus clouds off of Baja. This type of cloud cools the Earth. Source: NASA

But there is a lot of uncertainty around clouds, and in particular how their impact will evolve as the climate warms. A change in cloud cover of just a few percent can have a big impact on temperature. Cloud location and quality also matter. We see that clouds are moving higher and polewards with warming temperatures, which will further warm the planet. But we also see them getting wetter, which has a cooling effect. The factors that affect cloud formation, such as atmospheric and oceanic currents, are themselves affected by climate change. A NASA writeup from about ten years ago emphasizes the predictive difficulty, noting that while our climate models at the time could predict temperatures and winds to within about 5% accuracy, the predictions for clouds and rainfall were only accurate to within about 25-35%. The picture below shows the rainfall predicted, on average, by the end of the century by a set of 38 climate models used in the recent IPCC-5 report. The dotted areas indicate where 90% of the models agree on the sign of the change. You can see there is significant disagreement among models. For large areas of the globe, including most of the United States, it’s not clear if there will be more or less total precipitation. (3)

Average percentage change in total precipitation between 1981-2000 and 2081-2100 for a high-warming scenario, averaged over 38 models. Dots indicate where 90% of those models agree on the sign of the change. Source: CarbonBrief

Understanding cloud behavior is clearly very complicated.

Clouds Are Important
It is also very important. As our climate quickly warms, we need to adapt to changes like flooding, drought, wildfire, sea-level rise, and more. These adaptations are very expensive, costing trillions of dollars in aggregate, and can take one or more decades to build. We want to start them early, but if we don’t know which impacts will occur where, and to what degree, we can waste huge amounts of money and effort. Tapio Schneider, an atmospheric scientist at CalTech, is passionate about this topic. In a recent panel at MIT, he asserted: “We need to know now, and very urgently, what happens in the next few decades”. (4)

Schneider is leading a new modeling effort that is bringing together atmospheric scientists, data processing experts, and machine learning leads to improve the accuracy of our models. As he explains, the behavior of clouds includes very small-scale processes (e.g., droplet formation) as well as much larger-scale interactions, which is too much to compute explicitly. The joint project between CalTech, MIT, the Naval Postgraduate School, and NASA’s Jet Propulsion Laboratory is building adaptive models that focus more on the small-scale processes, with constant improvement from masses of new data being collected by aircraft and satellites. (5) Schneider believes that his team will have much more accurate models in the next 5-10 years, not just “because we have to”, but because it is a “golden age” to make progress. Much more high-quality data is available, machine learning techniques have greatly improved, and processing power is high. Investments in this work can have a big impact because the stakes are so large. “The estimated economic value of reducing uncertainties in climate predictions by half is trillions of US dollars in societal benefit,” he claims.

Clouds Are Problematic
We have learned over the past few years that clouds are cooling the planet more than we previously thought. This is a “double whammy” of bad news, as Schneider puts it, because it means:

1. The climate is more sensitive to CO2 increase than we have been thinking. That is, the temperature increases faster as CO2 increases, but it’s been masked by the clouds.

2. As warming air disrupts the low cloud cover, there will be a positive feedback that warms the planet even faster.

On the latter point, a recent report from his team indicates that if the CO2 levels triple, cloud cover will essentially disappear. What would have been a 4°C increase in overall temperature, due to the increase in CO2, would instead be a 12°C increase in temperature. Scientists believe this may have happened about 56 million years ago, explaining crocodile bones that were found in the Arctic. That level of CO2 increase is somewhat unlikely, but what happens with clouds and precipitation at more realistic and near-term levels is of paramount interest. Evidence has been building over the past decade that the low (cooling) clouds will dissipate, leading to warmer temperatures, but the size of the effect is still an area of active research.

What About High Clouds?
High clouds (cirrus clouds) tend to warm the planet. They are not very reflective and so provide mostly insulating capability. The interesting thing in this regard is that we are increasing the number of these clouds through our use of aircraft. So-called “contrail cirrus clouds” that are generated behind planes at high altitudes contribute more to the planet’s temperature today than the CO2 emissions from aircraft. While this effect doesn’t last -- if the contrails disappeared, the temperature increase would disappear within days, unlike with CO2 -- the effect is large. Contrails have a particularly big warming effect at night, when there is no sunlight for them to reflect. In areas with many persistent contrails (in the US, that is primarily the midwest, southeast and northeast), nights are relatively warm. One study found contrails reduce the daily temperature range (night vs day) by about 3C. Another study found that, in the days after 9/11 when plane flights were halted, the daily temperature range went up by 1.8C in areas where contrails are most prevalent. (6)

Contrails over San Francisco. Source: NASA

And yet Americans are flying more than ever. A recent study found that the warming effect from aviation will be three times larger in 2050 than in 2006 if we do not make changes. Researchers think that one of the best ways to reduce contrails, short of flying less, is to reduce the soot being emitted from the engines. (Soot particles help the contrails form.) Another option is to adjust flight routes so there will be fewer contrails, or so they will have less effect. Flying in areas with warmer or drier air can weaken the contrails. Flying over darker areas, during the day when the contrails can reflect the sun, can also reduce their warming impact. Changing flight routes can increase cost and emissions, but at least some studies have shown that those impacts can be kept relatively small.

I ran across this topic by accident when I was trying to understand why estimates for aviation emissions differ so much from one another. My reading made me realize that I have been taking clouds for granted, but we cannot do that as we continue to warm the planet. Clouds provide all-important cooling and precipitation that support a diversity of habitats on Earth. Scientists are working to understand how our cloud coverage will be affected by global warming, and what that means for regional climates around the globe. In the meantime, we can all do our part to reduce our own emissions and to encourage aggressive policies that will help protect our clouds and our ecosystems.

Notes and References
1. If you are interested in learning more about clouds and some of the current work on them, Quanta Magazine has a nice overview that includes a paleo perspective. I also like this writeup from NASA. Though not as recent, it has lots of good background and is easy to read while still being thorough. CarbonBrief has a shorter writeup about some of the modeling challenges, Cosmos Magazine reviews some research from Down Under, and this NASA writeup explains how cloud predictions affect models' overall estimate of climate sensitivity.

2. There is a short video here demonstrating that particles are needed to build a cloud.

3. There is more information about rainfall projections here, part of a series by CarbonBrief on climate models.

4. MIT has been hosting a series of climate symposia, and I found this panel on “Frontiers in Climate Science” to be particularly good, though I wish it had been longer.

5. You can read more about the Climate Modeling Alliance here.

6. This summary about the effect of contrails on climate is based on a nice writeup from Yale, as well as a shorter one from Inside Climate News.

Current Climate Data (December 2019 / January 2020)
Global impacts, US impacts, CO2 metric, Climate dashboard (updated annually)

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Posted by 800,000 years ago..., a resident of Charleston Meadows,
on Feb 10, 2020 at 5:14 pm

from your Climate Dashboard: Web Link

"The global average atmospheric carbon dioxide in 2018 was 407.4 parts per million (ppm for short), with a range of uncertainty of plus or minus 0.1 ppm. Carbon dioxide levels today are higher than at any point in at least the past 800,000 years."

....... the past 800,000 years.

Posted by Anon, a resident of Another Palo Alto neighborhood,
on Feb 11, 2020 at 5:56 pm

>> What would have been a 4°C increase in overall temperature, due to the increase in CO2, would instead be a 12°C increase in temperature. Scientists believe this may have happened about 56 million years ago, explaining crocodile bones that were found in the Arctic. That level of CO2 increase is somewhat unlikely

Unfortunately I'm not so sure. The question is, what CO2 concentration is required? According to some research, that previous level was only around 1000 ppm. Web Link

Posted by CrescentParkAnon., a resident of Crescent Park,
on Feb 11, 2020 at 10:27 pm

I just feel that if we as a species survive this it will only be by sheerest luck. I can only hope that I will be gone before the major issues we read about and others we may not have imagined hit us. This is the age of idiocy, almost everything that we are proud about is something that is doing lots of damage to the planet and each other - and preventing changes that we need to have to preserve our environment and bring justice and support to all the people of our planet.

What is required is a social order of cooperation, but human behavior since we have stopped being hunter-gatherers has been based on war and deceit. There is not even the language or a way to talk about what needs to happen to bridge the gap between two type of societies, one which we do not even know what it would be like, or have any idea how to get there.

I wish us all the best of luck, and wish everyone would start soon to slow down and consider stop living in an artificial world of bad ideas sold to us against our better interests by leveraging our worst characteristics against us, slow down stop participating in what is really a virtual war on each other and the planet. That means we have to stop respecting and mimicking the people who we raise up today and be mindful to support and repeat human values and behavior when we see it, and defend them when they are attacked.

Posted by Sherry Listgarten, a blogger,
on Feb 12, 2020 at 8:31 am

Sherry Listgarten is a registered user.

@CPA: Thank you, that was heartfelt! FWIW, I am more optimistic. If you think about it, the academics are doing their job. The scientists are doing their job. The entrepreneurs and bankers are starting to do their jobs. The journalists are doing their jobs. More and more city and state governments are doing their jobs. Peoples' attitudes are changing. And a few countries are nailing it. What is sorely missing is strong national leadership on climate from the US, and Republicans that care about this speaking up and finding common ground. With that, I think a lot would change. Everything else is primed.

BTW, I think this is a really interesting point you make: "There is not even the language or a way to talk about what needs to happen to bridge the gap between two type of societies, one which we do not even know what it would be like, or have any idea how to get there." The clearer our vision is of where we are going, the easier it is to get there. And the language we use to talk about this matters, but there are big gaps. I'll try to dig into this more at some point. Great observation.

Posted by I've Looked At Clouds From Both Sides Now, a resident of Barron Park,
on Feb 13, 2020 at 2:54 pm

Decades ago, there was a big deal made about 'acid rain' & its adverse effect on foliage.

Nothing happened of significant note.

"The sky is falling" said Chicken Little.

Posted by Sherry Listgarten, a blogger,
on Feb 13, 2020 at 4:15 pm

Sherry Listgarten is a registered user.

Thanks for bringing this up -- it's interesting and useful to look at the history of issues like this.

Can you clarify what you are saying? Are you saying there is/was no such thing as acid rain? Or that acid rain is/was real, but has no impact? Or that it had impact, but not on forests? Or that its impact is/was overstated? Or that it was an issue but we addressed it, for example via the 1990 Clean Air Act? Or ...? I'd love a reference or two as well, since I've always considered this to be something of a success story, in which Bush's environmental policy made a clear and measurable improvement.

Posted by Acid Rain Is Now China's Problem, a resident of Stanford,
on Feb 13, 2020 at 4:27 pm

Acid rain was mainly caused by emissions of sulphur dioxide to the atmosphere from coal-fired power stations, and by emissions of oxides of nitrogen from various sources. These gases, combined with water in the atmosphere to form sulphuric and nitric acids. The acids fell to earth as acid rain and studies purported to show acid rain damaged trees, polluted streams, lakes and rivers and damaged wildlife and buildings.

Acid rain was dealt with in the 1980s and 1990s. By switching from coal to gas and installing "scrubbers" to clean up power station and factory emissions, huge reductions were made in acid rain pollution in Europe. Catalytic convertors on car exhausts reduced nitrogen oxide emissions. The US Clean Air Act Amendments, designed in part to control sulphur dioxide emissions, were passed in 1990.

Emissions of sulphur dioxide and nitrogen oxides are now under control in Europe and America generally, but emissions from shipping still cause acid rain in coastal areas. Some experts warn that increasing acidity of the oceans could destroy all coral by 2065. Also, acid rain persists in China, which now burns half of all coal burned in the world annually.

Posted by 800,000 years ago..., a resident of Charleston Meadows,
on Feb 13, 2020 at 5:48 pm

"Nothing happened of significant note."

Sherry - God bless you, but why do you humor the hit-and-run posters who speak in AM talk radio bumpersticker-speak?

Like climate deniers, they live in their own reality where history, science and fact are irrelevant. You are admiringly polite, to those who have no interest in education, enlightenment or even engagement.

Seriously: "Nothing happened of significant note."



Posted by Anon, a resident of Another Palo Alto neighborhood,
on Feb 13, 2020 at 6:01 pm

Posted by I've Looked At Clouds From Both Sides Now, a resident of Barron Park,

>> Decades ago, there was a big deal made about 'acid rain' & its adverse effect on foliage.

>> Nothing happened of significant note.

Actually, governments and industries spent billions of dollars developing and installing equipment that would scrub SO2 from smelter and power plant exhaust. I recall seeing one installed in the mid-60's, as it happened. So, to say "nothing happened" is a misleading perspective, since the reason "nothing happened" is because "something else happened". It might interest you to know that the UK government/public/press became involved ca. 1930, and installations of a form of scrubbers began in 1930's (interrupted by the war). Web Link I found this history of Flue Gas Desulfurization online, dated 1977. It begins in 1850.

Web Link

>> "The sky is falling" said Chicken Little.

So, every time a disaster is averted, you like to repeat this? What do you say when the disaster is not averted?

Posted by Acid Rain Revisited, a resident of Barron Park,
on Feb 14, 2020 at 9:30 am

@ Acid Rain Is Now China's Problem
"Also, acid rain persists in China, which now burns half of all coal burned in the world annually."

^^This is on a positive note as acid rain is now China's problem because they are very non-environmentally conscious in their extensive manufacturing operations.

As long as the winds don't blow acid rain clouds into the USA, I could care less what goes on over there.

Posted by Sherry Listgarten, a blogger,
on Feb 14, 2020 at 2:40 pm

Sherry Listgarten is a registered user.

Just so people know, several of these posts are from the same person trying to clarify their position.

Many of the assertions made above are accurate. However, some are not. The point about ocean acidification is misleading since the primary source of that is absorption of CO2, not acid rain. And the "purported" terminology is also misleading because the attribution was shown in a variety of ways, such as using isotopic tracers in the smokestack emissions.

@Anon -- thank you for the information and references.

@800 -- I ask because I try to understand where the person is coming from and I often learn something. In this instance, it's a little harder because the person posts under several different names and cities, so it's not clear they are posting in good faith. They also do not provide references and they incorporate some misleading statements. Comments can be a weird place, but it's important to talk about these things, so for now I feel like the pros outweigh the cons.

Posted by musical, a resident of Palo Verde,
on Feb 15, 2020 at 11:59 am

^ Okay then, I'm curious, though off-topic, whether TERMS OF USE apply here.

"You agree not to post comments under multiple names. Postings within a single topic from the same IP address made under different names will be deleted."

Posted by Sherry Listgarten, a blogger,
on Feb 15, 2020 at 7:16 pm

Sherry Listgarten is a registered user.

@musical, yes, I expect those terms apply. But sometimes I think it's more interesting to leave the comments up. What can we learn from seeing who is choosing to amplify their own voice, and how, and then think about why that might be the case. And then think about how much of that goes on that we don't even detect.

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