Albedo Loss since 2001

[rob...@rtulip.net]

This chart shows the accelerating planetary darkening trend measured by NASA satellite data.

 

Source: Chart made by Robert Tulip from NASA CERES satellite data share by Professor Peter Cox of Exeter University at Climate Chat with Dan Miller 28 July 2025 time stamp 17:37  https://youtu.be/5rsIoJeveOM?t=1057

 

The accelerating trend line helps explain why nothing we do about carbon can make a difference to short term temperature increase.  This measured albedo loss, two watts per square meter over 25 years, with an apparent tipping point of acceleration around 2014, compares to annual increase of radiative forcing due to the greenhouse effect of about 0.038 w/m2. The drivers of this acceleration show no sign of abating, meaning that without direct climate cooling action to mitigate darkening we can expect heating to continue to accelerate.  Further discussion is in the attachment to my recent HPAC email on the melting of Antarctica.  Excel chart is attached.  I produced this by visually copying the data points in the chart shared by Professor Cox.

 

Regards

 

Robert Tulip

 

[Robin Collins]

Related, the unexpected albedo impacts of forest fires on glaciers. In today’s Globe and Mail.  

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[Jan Umsonst]

Hi all, 

just as a contribution - the neat total surface melt event of Greenland in 2012 for some 2 days if I remember correctly had been caused to some extent by soot deposition from Canadian wild fires

Further, highly relevant the soot deposition also will fuel algal growth which could become in a warmer climate the main reason for a darkening on Greenland. Fun fact: its self reinforcing as more algal growth increases surface melt, which then releases more nutrients.

We could have here the next massive underestimation underway...

Never underestimate a microbe, especially if it has supporting friends and family nearby...

All the best

Jan

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[rob...@rtulip.net]

Thanks Dan.  Your work is superb and I listen to Climate Chat avidly.  I don’t get why Hansen insists on using incoming rather than outgoing radiation as the denominator for albedo measurement.  It does not make sense.  Albedo is outgoing radiation, and as the chart below shows, that has fallen by 2% this century, not the 0.5% that Hansen derives from comparing the change to incoming radiation.  The Earth as viewed from space is now 2% darker than 25 years ago, not 0.5% darker as Hansen implies.  The quantum of absorbed radiation is not relevant to how bright the Earth is.  Compare this to a light bulb.  The brightness is how much light it gives off, not how much electricity comes in.

 

Regards,

Robert Tulip

 

From: Dan Miller <d...@rodagroup.com>
Sent: Friday, 5 September 2025 12:28 PM
To: rob...@rtulip.net
Cc: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>; Planetary Restoration <planetary-...@googlegroups.com>
Subject: Re: Albedo Loss since 2001

 

I had Jim Hansen on recently. He talked about this 0.5% loss of albedo over the past 25 years is indicative of a 4.5ºC ECS.  I also interviewed George Tselioudis on how cloud coverage is dropping due to global warming.

 

Leon Simons is also covering this on BlueSky and Twitter.

 

Best,

Dan

 

 

2014 also corresponds to when sulfate aerosols started dropping in China and 2020 is when they dropped dramatically over the oceans.  Since the effect is logarithmic, reducing aerosols over the pristine oceans has a much bigger impact than reducing aerosols over polluted China.

<image002.png>

<Albedo Loss Since 2001.xlsx>

 

[rob de laet]

This is such crucial information to understand the recent temperature hikes in 2023 and 2024. Thank you Robert!

Rob de Laet 

Project Lead Cooling the Climate

Member of the EcoRestoration Alliance

Fellow of Global Evergreening Alliance

Fellow fo the Schumacher Institute

Co-founder of Senang Eco Services

WhatsApp: +55 71 992617846

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[Jan Umsonst]

Hi all, here an important preprint if they are correct -

Decreases in anthropogenic aerosols in the Northern Hemisphere had been canceled out by increases in the Southern Hemisphere with only a marginal net effect

Would make the cloud feedback way worse...

"Negligible Contribution from Aerosols to Recent Trends in Earth’s Energy Imbalance"

During the 21st century, Earth’s energy imbalance (EEI) at the top of the atmosphere has markedly increased, mainly due to an increase in absorbed shortwave (SW) rather than a decrease in outgoing longwave (LW) radiation. While previous studies, based on single-forcing (aerosol-only) experiments, linked reductions in anthropogenic aerosols to this positive SW trend, we find that both aerosol-radiation interactions and aerosol-cloud interactions have had a negligible impact on recent increases in the EEI. We estimate recent trends in effective radiative forcing due to aerosols using observations and reanalysis data. While aerosol concentrations have declined in the Northern Hemisphere (NH), wildfires and volcanic activity in the Southern Hemisphere (SH) have resulted in larger aerosol loading. This contrast effectively cancels out the total aerosol forcing, resulting in a negligible global impact on the EEI trend. Our findings also suggest that model-driven estimates may be overestimated, as they overlook the compensating effects of SH aerosol emissions that balance out NH reductions.

"Negligible Contribution from Aerosols to Recent Trends in Earth’s Energy Imbalance" https://www.researchsquare.com/article/rs-5679586/v1

All the best

Jan

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[rob de laet]

Hi Jan, 

this is understood, but what I don't understand is the overall overemphasis on anthropogenic aerosols, while bioaerosols are much more important. They are produced by ecosystems. The weakening of the Earth's ''cloud factories'' over the oceans and forests are, in my mind, directly related to the decay of the ecosystems that regulate those particles, and are therefore a key factor in the decline of low clouds and the rise in global temperatures. 

The picture below shows this effect very clearly for the Congo and Amazon in 2023, both in record (and connected) drought, while the low cloud levels in the eastern tropical Pacific and Atlantic in this picture are likely caused by the El Nino, causing less upwelling (due to weak tradewinds) and thus less DMS production due to less plankton blooms, caused both by the ENSO cycle and the general decay of ocean biology. 

(PDF) Decline in ocean net primary production coincident with the 2023 heat wave

(PDF) Decline in ocean net primary production coincident with the 2023 h... PDF | Marine primary productivity is pivotal for transferring carbon dioxide from the atmosphere into the ocean....

Rob de Laet 

Project Lead Cooling the Climate

Member of the EcoRestoration Alliance

Fellow of Global Evergreening Alliance

Fellow fo the Schumacher Institute

Co-founder of Senang Eco Services

WhatsApp: +55 71 992617846

https://groups.google.com/d/msgid/healthy-planet-action-coalition/cdf1b4fa-c9be-46d1-9212-bff741c5cd45%40gmail.com

.

[Tom Goreau]

Albedo is defined as the fraction of incoming radiation that is reflected.

 

That’s why Hansen uses IR as the denominator.

 

OR is more variable due to stratospheric dynamics (IR depends on only solar dynamics).

 

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[Tom Goreau]

An author of this important paper gave a HPAC webinar very recently, and HPAC will soon post the link to it:

 

https://www.globalcoral.org/geoengineering-a-bad-idea-whose-time-has-come/

 

They make very clear that artificially increased albedo has a cost, and can only work as a short-term response to buy time to reduce GHG sources, and increase their sinks simultaneously, to reset Earth’s thermostat at safe levels.

 

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[Tom Goreau]

The atmosphere aerosol paper discussed global changes in total aerosols and sulfates, both with anthropogenic and natural sources. The key is that anthropogenic sources dominate in the North and natural ones in the South, due to the very different land/ocean ratios and human populations.

 

Thanks for the 2023 ocean productivity decline paper, Rob! The pattern of decline in productivity in hot ocean waters is very similar to that which affected corals that year:

 

T. J. F. Goreau & R. L. Hayes, 2024, 2023 record marine heat waves: Coral Bleaching HotSpot maps reveal global sea surface temperature extremes, coral mortality, and ocean circulation change, Oxford Open Climate Change, https://academic.oup.com/oocc/article/4/1/kgae005/7666987

 

We saw the same patterns in 2024 as well. I have to make final revisions to our paper on the 2024 global patterns.

 

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance

Chief Scientist, Biorock Technology Inc., Blue Regeneration SL

Technical Advisor, Blue Guardians Programme, SIDS DOCK

37 Pleasant Street, Cambridge, MA 02139

gor...@globalcoral.org
www.globalcoral.org
Phone: (1) 857-523-0807 (leave message)

 

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase

https://www.routledge.com/Geotherapy-Innovative-Methods-of-Soil-Fertility-Restoration-Carbon-Sequestration-and-Reversing-CO2-Increase/Goreau-Larson-Campe/p/book/9781466595392

 

Innovative Methods of Marine Ecosystem Restoration

https://www.taylorfrancis.com/books/oa-edit/10.1201/b14314/innovative-methods-marine-ecosystem-restoration-robert-kent-trench-thomas-goreau

 

On the Nature of Things: The Scientific Photography of Fritz Goro

 

Geotherapy: Regenerating ecosystem services to reverse climate change

 

No one can change the past, everybody can change the future

 

It’s much later than we think, especially if we don’t think

 

Those with their heads in the sand will see the light when global warming and sea level rise wash the beach away

 

“When you run to the rocks, the rocks will be melting, when you run to the sea, the sea will be boiling”, Peter Tosh, Jamaica’s greatest song writer

 

“The Earth is not dying, she is being killed” U. Utah Phillips

 

“It is the responsibility of intellectuals to speak the truth and expose lies” Noam Chomsky

 

 

 

From: 'rob de laet' via Healthy Planet Action Coalition (HPAC) <healthy-planet-...@googlegroups.com>
Date: Friday, September 5, 2025 at 20:30
To: healthy-planet-...@googlegroups.com <healthy-planet-...@googlegroups.com>, Jan Umsonst <j.o.u...@gmail.com>
Subject: Re: [HPAC] Albedo Loss since 2001

To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/954190694.563004.1757118644806%40mail.yahoo.com.

[rob de laet]

Dear Tom, 

thank you. Please keep us appraised of any data you have on 2024 as Peter Bunyard and I are eager to look at those!

Kind regards, 

To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/BY3PR13MB499489AD5AB8F0529B3EC2D5DD02A%40BY3PR13MB4994.namprd13.prod.outlook.com.

[rob...@rtulip.net]

Thanks Tom, this definition of albedo you give is a great example of the disconnect between science and popular thinking. 

 

Hansen speaks about the darkening of the world, describing “a substantial darkening of the planet (decreased albedo) equivalent to a CO2 increase of more than 100 ppm.” (Jan 2024) 

 

That concept of darkening is simple intuitive language that I have been using for some time.  But Hansen then reverts to albedo as a fraction of Incoming Radiation (IR).  This is jargon that makes his point confusing and obscure.  He speaks elsewhere about the frustration he experiences in communicating to the public, and this is a classic example of why his scientific training needs a journalistic edit for simplicity and cut-through.

 

Let me explain.  If you get a 100 lumen light bulb and paint it so it only shines with 98 lumens, then it makes sense to say it has got 2% darker.  We don’t measure its brightness against wattage (incoming electricity) except for measuring efficiency. 

 

Same with the Earth.  Viewed from the Moon, or any external point, the Earth is now 2% darker than 25 years ago, because the planet is emitting 2% less light.  Hansen calculates this darkening at due to loss of clouds (60%), aerosols (30%) loss and ice and snow (10%).  (12 Feb 2025, Fig SM 15 attached).  And as I have noted, since 2015 this darkening of 2 w/m² has produced over five times the extra heat that new emissions have caused (0.36 w/m²).

 

Saying the Earth is only 0.5% darker because albedo is a ratio of incoming wattage makes no intuitive sense. We need a light bulb moment here, applying the simple language of brightness and darkness that Hansen uses but then confuses. 

 

And on your final point, the annual variability of outgoing radiation (OR) is clearly shown in the initial chart, with a very pronounced 2% accelerating darkening trend. 

 

Regards, Robert

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[rob...@rtulip.net]

Hi Michael,

 

Thank you very much for these observations.

 

I don’t believe I, or anyone here, is trying to redefine albedo. My point is that planetary brightening and darkening are the most direct, intuitive ways to communicate the meaning of albedo change, and those concepts make most sense using past brightness as the baseline. Yes, albedo is by definition a ratio. But any ratio can be expressed in different, complementary ways.

 

For example, we can describe albedo loss since 2001 in two equivalent ways:

• In terms of watts: a drop from ~100 to ~98 W/m² of reflected shortwave radiation, i.e. a 2% planetary darkening.
• In terms of ratio: a fall from ~29.3% to ~28.8% of incoming radiation, i.e. about half a percent.

 

My sense is that the watts framing is clearer and more accessible, with the added simplicity that ~100 W/m² reflected can be treated as a practical baseline of “100% brightness.”

 

On your point that “albedo does not speak to absorbed radiation,” I would respectfully disagree. By definition, lower albedo means less reflection, and any energy not reflected must be absorbed. A 2% albedo loss this century is energy that has entered the Earth system as heat instead of being returned to space. Reflection and absorption are two sides of the same coin.

 

This change is enormous in climate terms: the absorbed heat from albedo loss since 2015 exceeds the forcing from new greenhouse gas emissions by a factor of five (~2.0 vs ~0.36 W/m²). That makes it essential to analyse reflection and absorption together, rather than treating them separately.

 

I strongly agree with you that all solutions must be considered. But if increasing reflection can deliver cooling more cheaply, quickly, safely and reliably than reducing emissions and GHG removal, then urgent priority should go to the most effective methods. Tragically, politics still lags far behind the physics.

 

Regards,

Robert Tulip

 

From: Michael Routh <mwr...@gmail.com>
Sent: Sunday, 7 September 2025 1:36 AM
To: Robert Tulip <rob...@rtulip.net>
Cc: Tom Goreau <gor...@globalcoral.org>; rob de laet <robd...@yahoo.com>; Dan Miller <d...@rodagroup.com>; healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>; Planetary Restoration <planetary-...@googlegroups.com>; Soden, Brian J <bso...@miami.edu>
Subject: Re: [HPAC] Albedo Loss since 2001

 

All,

 

While I believe that most on this thread agree that cooling on a global basis must become a more prominent part of the climate restoration conversation, please allow me to comment here regarding the use of the word “albedo."

 

Let’s not spend precious time trying to simplify by re-defining long-established scientific terms, as tempting as it is.  Yes, let’s translate complex concepts into something more easily digested by the broader audience…an admittedly significant challenge.

 

Albedo is simply defined:  the ratio of reflected radiation to incoming radiation.  Albedo does not speak to absorbed and re-emitted radiation.  Trying to combine incoming/reflection and absorption/emission into a single concept is where one needs to be careful not to confound these contributions to earth’s energy imbalance.  The net result of the two produces anomalies that we see today, but the contributions are distinct and different.

 

With earth’s incoming radiation assumed constant for illustration, and at the risk of oversimplifying, the combination of lower reflected light due to many factors (lower albedo), and greater absorption and/or lower re-emitted radiation due to increased atmospheric concentrations of absorbing materials (CO2, CH4, etc.), all contribute to the net energy imbalance and retained heat anomalies that earth is experiencing.  Our collective work to increase albedo (reflectivity), reduce absorption (lower GHG concentrations), and increase outgoing radiation to cool the earth can take many forms and offer different scale/speed/costs, all of which are likely needed to help restore more favorable earth system conditions for humans.

 

But please, let’s not object to, or try to redefine, these basic definitions.  Instead let’s put our energy into effectively articulating and developing our solutions in the context of how we envision attacking each of these anomalies in positive, scalable, fast, cost-effective ways.

 

Best regards,

 

Michael W. Routh, Ph.D.

 

.
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<Hansen Clouds Snow Ice Aerosol Albedo Loss.png>

 

[Robert Chris]

I'd like emphatically to endorse what RobertT has said below.

The mistake that Michael makes is evident from this sentence:

Our collective work to increase albedo (reflectivity), reduce absorption (lower GHG concentrations), and increase outgoing radiation to cool the earth can take many forms.

This makes it appear as if there are three independent processes at play.  But there are only two, and as Robert points out, they are interdependent.  What is not reflected must be absorbed.  That's a binary that is valid!  

But here's the error, reducing absorption (other than by reducing incoming sunlight) and increasing outgoing radiation are synonymous, they are not two different processes.  Outgoing radiation is only increased (relative to incoming radiation) by lowering atmospheric GHGs and thereby reducing the atmosphere's opacity to long wave radiation.

Reducing emissions and CDR/GGR reduce the atmosphere's opacity to longwave radiation, and SRM increases the amount of reflected sunlight.  There are only two processes at work, and the laws of physics bind them inseparably.

Regards

Robert

---

From: planetary-...@googlegroups.com <planetary-...@googlegroups.com> on behalf of rob...@rtulip.net <rob...@rtulip.net>
Sent: Sunday, September 07, 2025 11:11
To: 'Michael Routh' <mwr...@gmail.com>

Cc: 'Tom Goreau' <gor...@globalcoral.org>; 'rob de laet' <robd...@yahoo.com>; 'Dan Miller' <d...@rodagroup.com>; 'healthy-planet-action-coalition' <healthy-planet-...@googlegroups.com>; 'Planetary Restoration' <planetary-...@googlegroups.com>

Subject: [prag] RE: [HPAC] Albedo Loss since 2001

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[Michael MacCracken]

Dear Robert C--Let me offer just one nuance to consider, and that is that infrared emissions to space (outside of the CO2 bands) will depend on the layer of the atmosphere from which the infrared emissions are, on average, being emitted. This is the basis for the cirrus thinning approach to climate intervention in that if there are cirrus (can depend on cirrus thickness, etc.) at least a good share of the emission is from the very cold upper troposphere whereas if there is no (or little) cirrus, the emission to space could be coming mainly from the much lower and warmer marine stratus clouds, the water vapor that is concentrated in the lowest kilometer or two, or even the surface if there is a low amount of atmospheric water vapor.

I'd also note that in the visible, cirrus are poor reflectors of solar whereas marine stratus are good reflectors, and then solar is only an issue when the sun is up, whereas the role of clouds in the IR is going on day and night.

So, with regard to you definitive statement, clouds do matter, etc.

Best, Mike

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[Robert Chris]

Hi Mike

I'm a little confused by this.  I didn't mention clouds.  I recognise that they play an important (and complex) role in both reflecting shortwave and absorbing longwave radiation.

Are you refining my remark that 'Outgoing radiation is only increased (relative to incoming radiation) by lowering atmospheric GHGs and thereby reducing the atmosphere's opacity to long wave radiation.' by observing that by thinning cirrus clouds their warming from reflecting less energy to space than they reradiate to Earth would be reduced, allowing more longwave radiation to escape from lower altitudes?   I accept that this is an example of outgoing radiation being increased other than by lowering atmospheric GHGs.  Thanks for the note.

I must acknowledge that CCT is not something I've spent much time on.  In the grand scheme of things, is it likely to be significant when set against the cooling potential of increasing albedo or reducing atmospheric GHGs?  If it isn't, I suggest it's probably better ignored in the interests of not over-complicating the story for the wider public and policymakers. 

Regards

Robert

---

From: Michael MacCracken <mmac...@comcast.net>
Sent: Monday, September 08, 2025 18:47
To: Robert Chris <robert...@gmail.com>; rob...@rtulip.net <rob...@rtulip.net>; 'Michael Routh' <mwr...@gmail.com>

Cc: 'Tom Goreau' <gor...@globalcoral.org>; 'rob de laet' <robd...@yahoo.com>; 'Dan Miller' <d...@rodagroup.com>; 'healthy-planet-action-coalition' <healthy-planet-...@googlegroups.com>; 'Planetary Restoration' <planetary-...@googlegroups.com>

Subject: Re: [prag] RE: [HPAC] Albedo Loss since 2001

[Michael MacCracken]

Hi Robert--Yes, as I said it was a nuance on your remark.

And in the subtropics where the marine stratus are disappearing, it is unlikely that there would be cirrus due to the dryness of the air. So, yes, clouds can likely be ignored.

This time, here is a URL describing IOC plans on sulfur emissions from shipping: 
https://www.imo.org/en/mediacentre/hottopics/pages/sulphur-2020.aspx

It seems we will have to recover albedo without then--or having to reverse their plans.

Best, Mike

[Clive Elsworth]

Hi Robert C

 

You prompted me to ask the question below about the threat of thickening cirrus clouds.

 

Once again, cooling the oceans seems to provide a strong solution, by reducing both atmospheric water vapour and soot from wildfires.

 

Clive

 

Q. Are cirrus clouds thickening, e.g. from booming air travel? What other threats might cause further global warming by increasing the warming influence of cirrus clouds?

 

A. Yes, the evidence strongly suggests that cirrus clouds are thickening and expanding due to air travel, and this is contributing to global warming. Furthermore, other threats like increased atmospheric moisture and soot from wildfires could further amplify this warming effect.

Let's break down the science behind this.

 

1. The Direct Threat: Air Travel and Contrail Cirrus

When an aircraft flies through a cold, humid layer of the atmosphere, its engines release exhaust rich in water vapor and soot particles. This exhaust instantly freezes into millions of tiny ice crystals, forming a condensation trail (contrail).

• Short-Lived Contrails: Some contrails dissipate quickly if the air is dry.
• Persistent Spreading Contrails: If the air is sufficiently humid (in Ice-Supersaturated Regions), the contrail persists and spreads outward, often for hours. It morphs from a thin line into a vast, thin layer of cirrus cloud. This human-made cloud is called Contrail Cirrus.

 

The Warming Influence:
Natural cirrus clouds have a dual effect:

• Cooling Effect (Albedo): They reflect a small amount of incoming solar radiation (shortwave) back to space. This cools the Earth.
• Warming Effect (Greenhouse): They are very effective at trapping outgoing heat radiation (longwave infrared) emitted by the Earth's surface. This warms the Earth.

 

For the thin, high-altitude cirrus clouds formed by contrails, the warming effect overwhelmingly dominates the cooling effect. They act as insulating blankets in the sky.

Is it a significant problem? Absolutely.

Pre-pandemic, the net warming effect from contrail cirrus was estimated to be even greater than the warming from the entire aviation sector's cumulative CO₂ emissions. While CO₂ lasts for centuries, contrail cirrus only lasts for hours, but we are constantly creating new ones, making their instantaneous radiative forcing very strong.

 

2. Other Threats That Could Increase Cirrus Warming

Beyond direct air travel, other changes in the atmosphere could alter natural cirrus clouds to make them more warming.

 

a) Increased Atmospheric Water Vapor

Warmer air can hold more moisture. As global temperatures rise (primarily from CO₂ and other greenhouse gases), the atmosphere becomes more humid, even at high altitudes.

• Threat: More available water vapor means that any ice crystals that form in the upper troposphere can grow larger, potentially leading to thicker, more widespread, and longer-lasting cirrus clouds. This would enhance their heat-trapping (warming) effect.

 

b) More and Better Ice Nuclei

Ice clouds need a seed—a tiny particle—for the ice to form on. These are called Ice Nucleating Particles (INPs). The type and amount of INPs can dramatically influence cirrus cloud properties.

• Soot from Wildfires and Combustion: As wildfires become more frequent and intense due to climate change, they inject massive amounts of soot (black carbon) high into the atmosphere. Aircraft engines also produce soot. Soot particles are very effective INPs. More soot can lead to:
• More Clouds: More seeds mean more ice crystals can form.
• Smaller Crystals: With a fixed amount of water vapor, more seeds lead to more, but smaller, ice crystals. Clouds with smaller crystals have a larger surface area, which generally makes them more efficient at trapping heat.
• Dust from Desertification: Land use changes and drought can increase dust storms. Mineral dust is also a very effective INP and could have a similar effect to soot.

 

c) Changes in Atmospheric Circulation

Climate change is altering large-scale wind patterns (e.g., the jet stream). This could change where and how frequently Ice-Supersaturated Regions—the "flight corridors" where contrails form and persist—occur. If these regions become more common, the potential for contrail cirrus formation increases.

 

Summary Table

Threat	Mechanism	Impact on Cirrus Clouds
Air Travel (Contrails)	Soot and water vapor from exhaust provide nuclei and moisture for ice crystal formation in humid regions.	Creates entirely new, persistent Contrail Cirrus clouds that have a net strong warming effect.
Increased Water Vapor	A warmer atmosphere holds more moisture, even at high altitudes.	Provides more "fuel" for existing and new cirrus clouds to form, potentially making them thicker and more widespread, enhancing their warming effect.
More Soot (Wildfires, etc.)	Provides more effective seeds (Ice Nucleating Particles) for ice crystals to form on.	Could lead to more numerous, smaller ice crystals, creating denser cirrus clouds that are better at trapping heat.

 

Conclusion and The Path Forward

The thickening of cirrus clouds, both from air travel and other climate feedbacks, is a genuine and significant amplifier of global warming. It represents a classic climate feedback loop:

1. CO₂ warms the planet.
2. The warmer planet has more water vapor and possibly more wildfires.
3. This leads to more and thicker cirrus clouds.
4. These clouds trap more heat, causing further warming (positive feedback).

 

What can be done?
For aviation, the solution isn't to stop flying but to innovate. Strategies include:

• Sustainable Aviation Fuels (SAFs): These can reduce soot emissions by 50-70%, dramatically reducing the ice nuclei available for contrail formation.
• Flight Path Optimization: Using weather forecasting to allow planes to slightly alter their altitude to avoid ice-supersaturated regions, preventing persistent contrails from forming in the first place. This is a very promising near-term solution.

 

Understanding and mitigating the impact of cirrus clouds is a crucial frontier in the effort to combat climate change.

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[Michael Routh]

Hi Robert and Robert,

Thanks for your comments.

Re-reading my sentence that Robert C quoted, I realize I inserted a comma in the wrong place and probably oversimplified the statement, and that one might read that I was suggesting addressing  3 independent processes.  My intent was to point out that albedo and absorption/re-emission are distinctly different processes, albeit related as Robert T pointed out. 

A comment on “darkening” and “brightening”.  We should be mindful that it depends on whether you are viewing from space or from the earth’s surface.  For us scientists thinking about albedo and earth's reflectivity, the view is from space…putting aerosols in the stratosphere (SAI) will cause the earth to reflect more solar radiation and “brightens” the earth from that viewpoint…makes perfect sense.  But I suspect (from accounts written by the non-scientific press) that ordinary citizens are fearful that anything that blocks sunlight is a bad thing, i.e. SAI “darkens” the sun from their point of view on the ground…never mind that 1-2% won’t be discernible. While use of “brightening” and “darkening” may be useful from a scientific perspective, we might look for an easier way to articulate this to the fearful public.

That opinion stated, I believe most of us on this thread agree that solutions to increase reflectivity (SRM from TOA to surface) may provide the best payback in terms of time, scale, cost, and effectiveness, to cool the earth. Articulating that simply, demonstrating that practically, overcoming psychological fear of interfering with natural systems, and swaying political will, remain considerable challenges.

As others have said, reducing excess concentrations of legacy GHG’s…the impediment to outgoing IR radiation…is an equally important factor in restoring climatic conditions optimal for human life, even if it might take longer.  Some on this email distribution have expressed skepticism that solutions with sufficient scale, timing and cost-effectiveness to capture and sequester meaningful quantities of CO2 and CH4 are possible. That is a challenge that some of us are attempting to address, i.e. to amplify carbon capture and sequestration to remove many 10’s of GTs, with the expectation that when excess GHG concentrations are mostly removed, SRM can be retired, and earth system conditions will be much more favorable to humans.

Regards,

Michael

[Michael Routh]

All,

While I believe that most on this thread agree that cooling on a global basis must become a more prominent part of the climate restoration conversation, please allow me to comment here regarding the use of the word “albedo."

Let’s not spend precious time trying to simplify by re-defining long-established scientific terms, as tempting as it is.  Yes, let’s translate complex concepts into something more easily digested by the broader audience…an admittedly significant challenge.

Albedo is simply defined:  the ratio of reflected radiation to incoming radiation.  Albedo does not speak to absorbed and re-emitted radiation.  Trying to combine incoming/reflection and absorption/emission into a single concept is where one needs to be careful not to confound these contributions to earth’s energy imbalance.  The net result of the two produces anomalies that we see today, but the contributions are distinct and different.

With earth’s incoming radiation assumed constant for illustration, and at the risk of oversimplifying, the combination of lower reflected light due to many factors (lower albedo), and greater absorption and/or lower re-emitted radiation due to increased atmospheric concentrations of absorbing materials (CO2, CH4, etc.), all contribute to the net energy imbalance and retained heat anomalies that earth is experiencing.  Our collective work to increase albedo (reflectivity), reduce absorption (lower GHG concentrations), and increase outgoing radiation to cool the earth can take many forms and offer different scale/speed/costs, all of which are likely needed to help restore more favorable earth system conditions for humans.

But please, let’s not object to, or try to redefine, these basic definitions.  Instead let’s put our energy into effectively articulating and developing our solutions in the context of how we envision attacking each of these anomalies in positive, scalable, fast, cost-effective ways.

Best regards,

Michael W. Routh, Ph.D.

On Sep 6, 2025, at 8:55 AM, rob...@rtulip.net wrote:

[Tom Goreau]

Thanks, Clive, the threat of warming from increasing airplane condensation trails is very real!

 

A few years ago I was on a plane that flew over the Arctic to Guangdong in South China on route back to growing Indonesian coral reefs, the plane flew over barren Siberian tundra, the Gobi Desert, and then across the mostly densely populated part of East Central China. The atmospheric conditions were exceptionally favourable for the preservation of condensation trails: the air was supersaturated with moisture and there were no winds, so the condensation trails just stayed where they were, very slowly expanding but without drifting sideways, and each jet leaving a new sharper trail superimposed over earlier fuzzy ones.

 

Under these conditions the entire sky was crisscrossed with persistent condensation trails, hundreds of them in all directions, impossible to count out of an airplane window, there was more white condensation trails visible across the entire horizon than blue sky! Alas, I had no camera with me, but these are the ideal conditions for enhanced cirrus warming, and with the great increase in plane travel in China and India in recent years, we are bound to start affecting surface air temperatures from above too!

 

Michael MacCracken is old enough to remember when supersonic commercial jets were opposed because they could cause stratospheric clouds that would affect climate. Fortunately that threat did not develop, for economic reasons rather than technical ones, and the fact that the military did not see it as a potent weapon they had to have.

[Michael MacCracken]

Hi Clive--I want to suggest a bit of care on the more atmospheric water vapor argument. What more atmospheric water vapor will presumably mean is stronger convection as more energy/heat is released to power it (and more water vapor drawn in). Might it be that stronger convection will go higher and thereby wring out more of the water vapor so that air spreading out into the upper troposphere is actually drier and so might conditions become a bit less conducive to cirrus?

Just wondering.

Mike MacCracken

[Clive Elsworth]

Hi Mike

 

> Might it be that stronger convection will go higher and thereby wring out more of the water vapor..

I’m not qualified to answer that. This time (FWIW) I asked Grok:

 

Q. As global temperatures rise is there any reason why upper tropospheric air might become drier, leading to thinner cirrus clouds?

 

A. Yes, there is a proposed reason based on the "iris hypothesis," first put forward by climate scientist Richard Lindzen and colleagues in 2001. According to this idea, as global temperatures rise—particularly sea surface temperatures in the tropics—deep convective storms become more efficient at precipitating out moisture. This means more water vapor condenses and falls as rain lower in the atmosphere rather than being transported (or "detrained") upward into the upper troposphere as ice crystals or vapor. The result would be less moisture available in the upper troposphere, making it drier and thereby reducing the formation, extent, or thickness of high-altitude cirrus clouds, which are composed of ice crystals and form in that region. Thinner or fewer cirrus clouds would allow more outgoing longwave (infrared) radiation to escape to space, potentially acting as a negative feedback to limit further warming.

 

However, this hypothesis remains controversial and has not been widely supported by subsequent research. Numerous observational and modeling studies have found little to no evidence for a significant "iris effect," with some suggesting that any changes in cirrus clouds might instead produce a weak positive feedback that amplifies warming, or that the effect is overestimated or absent altogether. For instance, analyses of satellite data have shown inconsistencies with the predicted reduction in cloud cover, and the overall body of evidence points toward the upper troposphere generally becoming moister—not drier—with global warming, due to increased evaporation and atmospheric capacity for water vapor in a warmer climate.

 

Clive

 

P.S. It listed 34 references! Here are the first five:

 

How Atmospheric Water Vapor Amplifies Earth's Greenhouse Effect

Because warmer air holds more moisture, its concentration of water vapor increases. Specifically, this happens because water vapor does not ...

science.nasa.gov

 

Global warming at near-constant tropospheric relative humidity is ...

The AR6 was even more cautious, stating only that (it is likely that) human influence has contributed to moistening in the upper troposphere ...

nature.com

 

Response of upper tropospheric water vapor to global warming and ...

The results indicate that global warming and ENSO are the primary factors contributing to water vapor variations in the upper troposphere.

pmc.ncbi.nlm.nih.gov

 

Water vapor in the upper atmosphere amplifies global warming

A new study shows that water vapor high overhead and the temperature at the Earth's surface are linked in a climate feedback loop.

csl.noaa.gov

 

Upper-tropospheric moistening in response to anthropogenic warming

Water vapor in the upper troposphere strongly regulates the strength of water-vapor feedback, which is the primary process for amplifying ...

pnas.org

[Michael MacCracken]

Hi Clive--the really controversial aspect of the Lindzen hypothesis had to do with changes in cloud cover and, as I recall, the notion that there was no way for ocean surface temperature to exceed something like 30 C. I don't recall if there was questioning of the upper troposphere getting drier. References do seem to indicate tendency is for upper tropospheric moistening. There is, however, a real challenge for models in simulating the vertical moisture loading given that its mixing ratio changes by something like 4 orders of magnitude as one goes up through the troposphere, so a real challenge for the numerical representation of the changes

Mike

[Jan Umsonst]

Hi all, there exist a science cluster on upper tropospheric warming - if I remember right it's warming faster than the surface which increases atmospheric stability which is the reason for deep convection needing more energy in the tropics. 

This then leads to higher SST needed for deeper convection. On the other side convection is clustering more. Should be one reason for ITCZ contracting. 

The net effect is more water vapor in the upper tropical troposphere which is the main reason for the faster warming of the upper tropical troposphere. Do not know if more water vapor in the upper troposphere is a global trend - but do not think so but maybe wrong - but overshooting convection is now also increasingly observed in the mid latitudes and starting in higher latitudes - so maybe a signal evolving - hot spot regions like western boundary currents frontal system that intensify - more stronger lows.

Further, the massive marine heatwave will likely now start to induce a massive storm signal - upper water column accumulates fast heat in this region - so maybe a signal emerging 

Here one recent paper:  

Resolving the 21st century temperature trends of the upper troposphere–lower stratosphere with satellite observations

https://www.nature.com/articles/s41598-023-28222-x

Mistakes possible but should be correct...

All the best

Jan

P.s. grok is maybe the worst llm - musk nazified it!

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[Tom Goreau]

Lindzen claimed that the ocean surface could never get warmer than 30C because higher temperatures would induce a strong negative cloud cooling feedback.

 

He concluded there was no need to worry about global warming from GHG increases, because they would correct themselves.

 

In fact we are seeing ocean surface temperatures get well above this, with no signs of self-control cooling……

 

It’s just another fairy story from a simple minded model extrapolated beyond its limits, and in fact no one took his suggestion seriously apart from oil companies and right-wingnuts.

[Jan Umsonst]

Hi all, 

just checked the newest paper on tropospheric water vapor - El Ninos increase it La Ninas decrease it with a mean increasing trend that diminishes poleward.

The graphs are from this study:

"Response of upper tropospheric water vapor to global warming and ENSO"; https://www.nature.com/articles/s41598-024-56639-5#Fig8

 

And here the NOAA table of precititable water - what is interesting that the signal since 2023/24 El Nino is not really receding - somewhat but not too much: https://psl.noaa.gov/cgi-bin/data/timeseries/timeseries.pl?ntype=1&var=Precipitable%20Water&level=2000&lat1=90&lat2=-90&lon1=0&lon2=360&iseas=0&mon1=0&mon2=0&iarea=1&typeout=1&Submit=Create%20Timeseries

All the best

Jan

[Robert Chris]

Dan's short note has provoked me into writing a little explainer.  I hope it clarifies the relationship between albedo, brightness, and incident and reflected light.

Some high school maths to lay to rest this discussion about how changes in albedo should be expressed.  But first some definitions.

Luminance refers to the amount of light that is reflected by a surface. Illuminance refers to the total amount of light falling on a surface. It indicates how much light is available for reflection.  Luminosity is a measure of the total energy output of a light source.  Brightness is a subjective measure of the light emanating from a surface, including both reflected light and light generated at the surface.  Brightness is inversely proportional to the square of the distance between the observer and the source.  Albedo is the ratio of luminance to illuminance.  Formally, albedo is a measure of reflectance, not of brightness.

Albedo is expressed either as a ratio or a percentage.   Only light energy is accounted for by albedo.  Heat energy radiated from a surface is not included.

Let us suppose, to keep the maths simple, that a body receives 100 units of light and reflects 30 of them, i.e. illuminance of 100 and luminance of 30.  This body has an albedo of 0.3 or 30%.

The question is how the albedo and brightness change if either the illuminance or luminance changes.  In the example above, if the incoming light (illuminance) increases to, say, 150 units but the reflected light (luminance) remains at 30 units, then the albedo falls to 0.2 or 20% (30/150).  In this case, the brightness of the surface has not changed because seen from the same distance, it will be emitting the same amount of light.  But its albedo is reduced by a third.

If the albedo remains the same, the reflected light (luminance) would be 45 units (30% of 150) and it would appear to our distant observer to be one and a half times brighter than before because it was reflecting one and half times as much light.  Despite the albedo not changing, the effect of increasing the incident light (illuminance) causes the luminance also to increase, and the brightness correspondingly.

Now let’s suppose that the amount of incoming light (illuminance) remains the same but the amount reflected (luminance) falls from 30 to 15 units.  The albedo falls to 0.15 or 15% (15/100).  The albedo has halved.  In this case, the light reflected (luminance) and the brightness of the surface have also halved because half the amount of light has been reflected.

Referring this to Earth and recent changes in its albedo. Illuminance is, for all practical purposes, a constant 340 Wm-2.  In 2000 its luminance was ~100 Wm-2. Since then its luminance has fallen by ~1.7 Wm-2.  This represents a reduction of 0.5% in Earth’s albedo (1.7/340).  However, it represents a reduction of ~1.7% (1.7/100) in its luminance and a corresponding decrease in its brightness.

In conclusion, it is important to remember that albedo is a measure of reflectivity, not of brightness.  Reflectivity is a feature of the surface and is independent of the amount of incident light (illuminance) – if illuminance increases and the surface reflectivity (albedo) remains unchanged, its luminance will increase so as to maintain an unchanged albedo.  On the other hand, if the surface properties change and it reflects a lower proportion of the incident light, the albedo will decrease.  Whether its luminance and brightness also change depends on whether incident light (illuminance) also changes, something which does not apply in the case of Earth as its illuminance is constant.

I hope this helps.

Regards

RobertC

---

From: planetary-...@googlegroups.com <planetary-...@googlegroups.com> on behalf of Dan Miller <d...@rodagroup.com>
Sent: 06 September 2025 01:07
To: rob...@rtulip.net <rob...@rtulip.net>

Cc: healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>; Planetary Restoration <planetary-...@googlegroups.com>

Subject: [prag] Re: Albedo Loss since 2001

 

Albedo is how much energy Earth reflects away, not how much radiation it emits. Most of the energy the Earth emits is due to black body radiation (which is proportional to the fourth power of temperature) and that has nothing to do with albedo.  Albedo is how “bright” the Earth is and tells us how much of incoming solar radiation is reflected back to space before it has a chance to increase the temperature of the Earth.  

So albedo is not like a light bulb.  It’s how reflective a surface is.

Dan

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