Clouds the Likely Cause of Increased Global Warming in Latest Generation of Climate Models

Sky Clouds

Newly updated climate models in the CMIP6 project show a wider range of responses to carbon dioxide, with some indicating higher sensitivity and potentially greater warming.

New representations of clouds are making models more sensitive to carbon dioxide.

As scientists work to determine why some of the latest climate models suggest the future could be warmer than previously thought, a new study indicates the reason is likely related to challenges simulating the formation and evolution of clouds.

The new research, published in Science Advances, gives an overview of 39 updated models that are part of a major international climate endeavor, the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The models will also be analyzed for the upcoming sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC).

Compared with older models, a subset of these updated models has shown a higher sensitivity to carbon dioxide – that is, more warming for a given concentration of the greenhouse gas –though a few showed lower sensitivity as well.  The end result is a greater range of model responses than any preceding generation of models, dating back to the early 1990s.  If the models on the high end are correct and Earth is truly more sensitive to carbon dioxide than scientists had thought, the future could also be much warmer than previously projected. But it’s also possible that the updates made to the models between the last intercomparison project and this one are causing or exposing errors in their results.

In the new paper, the authors sought to systematically compare the CMIP6 models with previous generations and to catalog the likely reasons for the expanded range of sensitivity.

“Many research groups have already published papers analyzing possible reasons why the climate sensitivity of their models changed when they were updated,” said Gerald Meehl, a senior scientist at the National Center for Atmospheric Research (NCAR) and lead author of the new study. “Our goal was to look for any themes that were emerging, especially with the high-sensitivity models. The thing that came up again and again is that cloud feedbacks in general, and the interaction between clouds and tiny particles called aerosols in particular, seem to be contributing to higher sensitivity.”

The research was funded in part by the National Science Foundation, which is NCAR’s sponsor. Other supporters include the U.S. Department of Energy, the Helmholtz Society, and Deutsches Klima Rechen Zentrum (Germany’s climate computing center).

Evaluating model sensitivity

Researchers have traditionally evaluated climate model sensitivity using two different metrics. The first, which has been in use since the late 1970s, is called equilibrium climate sensitivity (ECS). It measures the temperature increase after atmospheric carbon dioxide is instantaneously doubled from preindustrial levels and the model is allowed to run until the climate stabilizes.

Through the decades, the range of ECS values has stayed remarkably consistent – somewhere around 1.5 to 4.5 degrees Celsius (2.7 to 8.1 degrees Fahrenheit) – even as models have become significantly more complex. For example, the models included in the previous phase of CMIP last decade, known as CMIP5, had ECS values ranging from 2.1 to 4.7°C (3.6 to 8.5°F).

The CMIP6 models, however, have a range from 1.8 to 5.6°C (3.2 to 10°F), widening the spread from CMIP5 on both the low and high ends. The NCAR-based Community Earth System Model, version 2 (CESM2) is one of the higher-sensitivity models, with an ECS value of 5.2°C (9.4°F).

Model developers have been busy picking their models apart during the last year to understand why ECS has changed. For many groups, the answers appear to come down to clouds and aerosols. Cloud processes unfold on very fine scales, which has made them challenging to accurately simulate in global-scale models in the past. In CMIP6, however, many modeling groups added more complex representations of these processes.

The new cloud capabilities in some models have produced better simulations in certain ways. The clouds in CESM2, for example, look more realistic when compared to observations. But clouds have a complicated relationship with climate warming – certain types of clouds in some locations reflect more sunlight, cooling the surface, while others can have the opposite effect, trapping heat.

Aerosols, which can be emitted naturally from volcanoes and other sources as well as by human activity, also reflect sunlight and have a cooling effect. But they interact with clouds too, changing their formation and brightness and, therefore, their ability to heat or cool the surface.

Many modeling groups have determined that adding this new complexity into the latest version of their models is having an impact on ECS. Meehl said this isn’t surprising.

“When you put more detail into the models, there are more degrees of freedom and more possible different outcomes,” he said. “Earth system models today are quite complex, with many components interacting in ways that are sometimes unanticipated. When you run these models, you’re going to get behaviors you wouldn’t see in more simplified models.”

An unmeasurable quantity

ECS is meant to tell scientists something about how Earth will respond to increasing atmospheric carbon dioxide. The result, however, cannot be checked against the real world.

“ECS is an unmeasurable quantity,” Meehl said. “It’s a rudimentary metric, created when models were much simpler. It’s still useful, but it isn’t the only way to understand how much rising greenhouse gases will affect the climate.”

One reason scientists continue to use ECS is because it allows them to compare current models to the earliest climate models. But researchers have come up with other metrics for looking at climate sensitivity along the way, including a model’s transient climate response (TCR). To measure that, modelers increase carbon dioxide by 1% a year, compounded, until carbon dioxide is doubled. While this measure is also idealized, it may give a more realistic view of temperature response, at least on the shorter-term horizon of the next several decades.

In the new paper, Meehl and his colleagues also compared how TCR has changed over time since its first use in the 1990s. The CMIP5 models had a TCR range of 1.1 to 2.5°C (2 to 4.5°F), while the range of the CMIP6 models only increased slightly, from 1.3 to 3.0°C (2.3 to 5.4°F). Overall, the change in average TCR warming was nearly imperceptible, from 1.8 to 2.0°C (3.2 to 3.6°F).

The change in TCR range is more modest than with ECS, which could mean that the CMIP6 models may not perform that differently from CMIP5 models when simulating temperature over the next several decades.

But even with the larger range of ECS, the average value of that metric “did not increase a huge amount,” Meehl said, only rising from 3.2 to 3.7°C (5.8 to 6.7°F).

“The high end is higher but the low end is lower, so the average values haven’t shifted too significantly,” he said.

Meehl also noted that the increased range of ECS could have a positive effect on science by spurring more research into cloud processes and cloud-aerosol interactions, including field campaigns to collect better observations of how these interactions play out in the real world.

“Cloud-aerosol interactions are on the bleeding edge of our comprehension of how the climate system works, and it’s a challenge to model what we don’t understand,” Meehl said. “These modelers are pushing the boundaries of human understanding, and I am hopeful that this uncertainty will motivate new science.”

Reference: “Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system models” by Gerald A. Meehl, Catherine A. Senior, Veronika Eyring, Gregory Flato, Jean-Francois Lamarque, Ronald J. Stouffer, Karl E. Taylor and Manuel Schlund, 24 June 2020, Science Advances.
DOI: 10.1126/sciadv.aba1981

11 Comments on "Clouds the Likely Cause of Increased Global Warming in Latest Generation of Climate Models"

  1. WARNING! WARNING! WAKE UP EVERYBODY! We have a major problem on Earth. And why the hell am I the only one on Earth sounding the alarm? Satellite photos from the 1960’s till now has shown that global warming has been going on since the 1960’s when jet engine airplanes started flying and China started their massive polluting industrial buildup. Take a look at the 1960’s photos and you can see how the weakest part of ice, which is permafrost, was the first thing that started melting in mass around Russia and China area of the planet. There is photo evidence of this warmer melted water from the melting permafrost draining into the area around Russia and China’s coastline. The photos show warmer melted permafrost water over time traveling into the Arctic Sea and the area around Russia’s side of the North Pole where, in the photos, shows how that warmer water has since the 1960’s been melting the ice of the North Pole. In the photos you can see how that warmer melted permafrost water traveled from Russia and over the years till this day has been not only melting the North Pole ice but has resulted in warming the waters of the world through the water circulation systems of the world. This also resulted in the ice and permafrost to be melting around the whole Arctic area. This melting of all the permafrost and ice on the Earth will go on till it is all gone unless we immediately shut down all the ways us humans are warming up the Earth. If we don’t stop it then it should take another 15-20 years for the North Pole’s ice to be completely melted and about 15-25 years for the South pole to be completely free of ice. When all that happens then the Earth will be in a new uncharted era where I’m sad to say not one of you even know what that will be! For then will be the unavoidable, irreversible, frightening, chaotic new world which those still alive will have to face! There is no plan to stop this from happening! There is not even any discussion of this! Trump and the Republicans don’t even believe in global warming and won’t do anything to stop it but will do a lot to make global warming worse! NASA and ALL the scientist of the world don’t talk about any of this. They are interested in taking our money and looking at other planets instead of figuring out how we are to live on Earth!
    So folks, since no one has offered any plan to avert this catastrophe you will face but me let me present it to you and hopefully you will wake up before you all die a horrific death of some kind in the future as the Earth takes it’s last breath of existence as we know it. Folks, we have to entirely change our lifestyles, our way of living. We have to stop flying turbo jet planes of all kinds first! These jets are gigantic vacuum machines that are vacuuming up, heating up and polluting enough air to fill the AstroDome every 2 minutes. There are about 90,000 jet engine plane flights a day worldwide and that doesn’t include military aircraft worldwide. Figuring on the low side that there is about a 3 hour flight for every flight we are flying jet planes that are sucking up, burning up and polluting enough air to fill about 194,400,000 Astrodome size stadiums! And that figure doesn’t even include military flights of any kind from any country worldwide! The heat from these jet planes ranges from 800 to 1200 degrees for passenger planes and 1200 to 2500 degrees for military planes. The Earth’s atmosphere cannot cool itself off or provide enough moisture in the atmosphere to make clouds after an everyday onslaught of more than about 230,000,000 Astrodome size stadiums of hot, polluting air every day attacking it! Now you may look at the sky and think that there is unlimited space up there in the sky for all the heat and pollution to go to every day. But think about this. We have people who climb up to the highest mountains in the world and when the get up to the top of the mountains they are at the area of the Earth where clouds are formed. So if they were to look down after being on top of the mountain they would see that it isn’t that far from the ground to where the clouds form around the Earth. So don’t think that you can heat up the atmosphere without any problem because when you look for the top of that highest mountain you realize that the Earth’s clouds can easily be affected by what we do. So it’s important to save the Earth’s clouds as much as we can in every way we can because clouds are actually the Earth’s umbrella from the Sun. Without clouds the Sun would roast the Earth into being like Mars and Venus which is exactly what will happen in about 20 to 30 years when there is no more ice or snow on Earth to make cold weather and no more clouds because the sun evaporates all moisture from the Earth, be it moisture as water on Earth or water vapors molecules in the sky, which results in there being no more clouds worldwide or too few clouds to make rain which is where we are at in parts of the world. Read my Facebook page of Ron McCune from Chicago, Illinois to get more info on how to avert this problem or else you will ALL die in about 20 to 30 years!

  2. Clyde Spencer | June 27, 2020 at 8:14 pm | Reply

    I’ll be lucky if I live another 20 years. And very unlucky if I live another 30!

  3. Reaching hard and coming up with such utter rubbish such as “blame the clouds” is a new level of unacceptable hand waving and religious catastrophism, from a group of hacks who cannot be trusted with anything that might explode.

  4. Stephen Pearcy | June 28, 2020 at 8:42 am | Reply

    The deniers constantly accuse the scientists of manipulating models to make it appear the situation is worse than it actually is. And the deniers will do it again with this story. But how do they explain the fact that the models (for years) had been underestimating the impact?

  5. I wonder some country used a nuke that caused all the dust to come over and left radiation flying through the northern Europe area and maybe in the sand too

  6. Bill Gates needs to stop playing god and the aerosol assaults on our skies needs to stop! Clouds don’t even look the same as they did last year, am I the only one who notices this? We need to reduce carbon emissions and do more work in alternative energy sources.

  7. No problem.BS means bad science. I’m sure it makes crazy people happy to name their phobia.

  8. Oh so now its the clouds fault, despite the fact that much needed rain water comes from clouds. WTF are you people smoking?

  9. Satellite pictures on the 1960s? lol
    We have the best possible experiment in decades just passed: at no time have emissions and industrial output been scales back this much for a handy 90 to 150 day period. And yet Mauna Loa claims carbon dioxide has not changed at all… Whether that’s true or not we had a huge decrease in air traffic and aerosols and it should modulate any accurate model.

  10. When science has 39 models that all predict some range of 1.2 deg C to 3.7 ish deg C increase and the NSIDC data shows arctic sea ice concentration stabilizing since 2012, and the increase in temperatures have not been realized, I think its all incorrect. Too many answers and not enough questions. the models don’t work. How many deg C per part per million by volume does CO2 contribute to warming?

  11. Gerald Lundquist | June 29, 2020 at 12:14 pm | Reply

    Ron McClure has valid points. It is refreshing to read an article written with some thought other than the prescribed predetermined theoretical information fronting CO2 as the reason! I would however argue that it is because of the increased moisture in the atmosphere that Earth is warming.
    I would also like to thank SciTech for being more open-minded than many scientist and allowing opposing views to be presented. I do agree with Ron that if we don’t act soon, it’s going to be catastrophic. Let’s have the discussion – it is not important that I be right – it is important that WE get it right!! Here is my theory – take a shot at it. I would love to have your comments by email [email protected]

    The Furnace Theory and Moisture Mesh Effect
    (please refer to the accompanying CO2 and Moisture references)

    Global Warming can be compared to a natural gas home furnace. In a furnace there is a pilot light whose function is to ignite the full-heat gas. Without a spark or a pilot light, the gas will not light. Once the gas is ignited by the pilot light, the flame can continue on its own without the pilot (similar to a small butane torch). Earth’s atmospheric Green House Gas’ operate in a similar fashion. Now that moisture is dominating, any small change in CO2 has no effect.

    Over millions of years GHG has evolved to a point where today Earth’s temperature is stable enough to support life. CO2 could be compared to the pilot light and water / moisture compared to the full heat gas in a furnace. Because CO2 is a gas a -78C, it retains a minimal amount of solar heat even at very cold temperatures. This thermal retention, aids in the melting of ice and sublimation of ice to moisture. The moisture with its’ superior ability to retain heat, combined with CO2, allows water to remain liquid during the night. Over thousands of years, moisture concentrations have developed to a point where CO2 GHG effect is minimal. Like a pilot light in a furnace, a significant percentage increase in CO2 is only minimal compared to the increase in the main gas availability of moisture. CO2 is effective at very low temperatures but is not dominant at temperatures above freezing, when there is a high amount of the more dominant moisture.

    Here are the easy to comprehend reasons the atmosphere is warming:
    • The world’s population has grown from 1.7 to 7.5 billion since 1900 and people’s personal demands have increased significantly.
    • Infrastructure (roads, buildings) has increased significantly, replacing vegetation and increasing solar heat intensity and retention. The countries where the greatest infrastructure exists (USA, China, India) are in or near the tropics where solar intensity and population are the greatest.
    • Atmospheric moisture is the most dominant GHG and has increased in concentration in conjunction with the warming provided by infrastructure. The moisture molecule is 4 times as heat absorbent as CO2. In most tropical countries atmospheric moisture is between 10,000 and 25,000 ppm while CO2 is relatively consistent at approx. 400 ppm.
    • Particulate (soot) has increased. Combined with moisture it is a super effective GHG. Canada has stringent emissions standards reducing particulate. Many countries in or near the tropics don’t!
    • Sewage in many countries, especially along the tropics, is emitted untreated into the oceans adding thermal heat and particulate. Sewage in tropical countries often runs on the surface or just under the surface, increasing its’ thermal pollution.
    • Garbage is dumped directly into the oceans converting solar light to heat.
    Standing in a parking lot on a hot summer’s day it should be easy to comprehend how the above would easily contribute to a 1.5 degree Celsius increase in atmospheric temperature.

    Moisture Mesh Effect (MME)
    It would be better to focus on atmospheric moisture and solar intensity than to continue the flogging of CO2. Call it the Moisture Mesh Effect (MME). The Moisture Mesh, if draped around the world, would be a heavy fabric at the tropics blending to a light crochet at the poles. Heat escapes much easier near the poles. This is important when considering atmospheric heat retention.

    Take a look at a globe (as opposed to the exploded northern view on a computer screen) and understand that the greatest solar intensity is between the tropics, with significant solar intensity as far as 40 degrees latitude north and south. This is also the area of greatest atmospheric moisture. Moisture both absorbs solar short wave energy as heat, and absorbs outbound long wave radiation from Earth. The simple fact is that the sun warms the Earth and moisture provides the insulation to maintain that heat over a longer timeframe.

    The atmospheric moisture and solar intensity is greatest the closer you get to the equator and the tropics. In the northern regions there is little solar intensity and minimal atmospheric moisture, except during the summer. Less solar heat is created and there is less moisture insulation, allowing for heat loss through the troposphere and into the stratosphere.

    The second law of thermal dynamics states that heat always flows from the warmest to the coolest regions. With limited MME in the northern Canadian region, and distant from the ocean, it makes sense to produce in Alberta and Saskatchewan as opposed to regions in the tropics. I realize this is not complicated which leaves people wondering how the Green House Effect could have come to be. Nobody believes that bright people who claim to be scientists could dismiss such a simply analogy like the MME. It appears that Scientists have been lost in the calculations, and nobody dares to question. Five years ago, I believed in the GHE until someone actually posed the question to me. That led me on the search for the explanation.

    The IPCC state that GHG’s are effective because they reflect long wave radiation back at earth. The term they use is “forcing”. According to the second law of thermal dynamics forcing is not possible.

    Scientists have excellent communication skills and are great with presentations. The can write lengthy reports citing each-others work, stating the same story over and over but never do they first identify:
    1. How do they come to calculate CO2 as 25% of the global warming factor?
    2. How can they calculate the CO2 GW factor relevant to moisture concentrations when moisture concentrations and solar intensity varies so significantly in different regions and during different seasons?
    3. Where have they include the above mentioned “easy to comprehend” GW factors in their climate models? Scientist are always quick to shuffle moisture out of the equation.
    4. If CO2 absorbs heat, how long does it retain heat – for micro-seconds? That fact is not disclosed. (It is obvious that moisture holds heat, but how long does CO2 retain heat?)
    5. Climate scientists never explain how “forcing” can defy the second lay of thermal dynamics!

    Modern scientist, many of them employed in the “industry” claim that CO2 is a major Climate Change factor. They claim “it’s complicated” indicating it takes extreme brilliance to understand. Many others don’t agree that CO2 has a significant effect. In Canada, and other small northern European countries the CO2 myth has momentum. In other parts of the tropical world, where global warming should be a concern, it is disregarded. Are we really that smart or are we simply misinformed. Before forcing more industry from Canada we need to have an open debate on CO2 as a global warming factor and review climate change in general.

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