Restoring the Great Barrier Reef

[Sev Clarke]

Colleagues,

Dr. Daniel Harrison’s recent presentation to HPAC, see https://healthyplanetaction.org/guest-speakers/  on how marine cloud brightening (MCB) might save the Great Barrier Reef (GBR) was both excellent and well-received. At the latter part of the discussion that followed, I itemised six of the challenges his proposed method had yet to overcome before it could become practical. These were that:

1. the seawater droplet or sea salt aerosol particle size distribution achieved was still sub-optimal
2. the rate of droplet formation was insufficient (by some two orders of magnitude, 10^^15 not 10^^17/sec)
3. the production was too energy intensive to be used at scale. (Daniel said it had to be reduced some 30-fold)
4. using crewed ships as the delivery platforms is too expensive
5. the method requires such restrictive conditions of humidity, existing cloud cover, and cloud condensation nuclei (CCN) density as to render it of doubtful practical value, and
6. being powered by fossil-fuel, rather than renewable energy, makes it problematic.

Furthermore, it is submitted that if the huge volume of the top few to several metres of ocean water over the GBR is to be cooled sufficiently to bring back the coral, then the cooling and shading of the over-warm water in and entering the Reef is likely to be needed long before and also far upwind and up-current (it flows West at 20°S onto the GBR where it splits N and S) of the Reef itself. Indeed, that ocean cooling by reflective aerosol, cloud or surface water solar reflection would probably need to take place over thousands of kilometres distant, perhaps as far afield as the Melanesian islands of Fiji (3,000km E and 15°S) or New Caledonia (1,700km E and 22°S), and possibly further.  It should be noted that the prevailing winds from Coral Sea+ islands upwind of the GBR typically bring cooling cloud to the GBR. 

Such cooling might be achieved using combinations of my four, proposed, climate restoration methods: Buoyant Flakes, Nanobubbles, Seatomisers and AMRAerostats. 

 

Challenges 1 & 2 are addressed in five ways. The first is by Atmospheric Methane Removal Aerostats which would release 20-50nm (av. ~30nm) diameter iron salt aerosols (ISA) of ferric chloride over the ocean, typically from off-island installations, at altitudes from 500-2,000m. The aerosol particle size distribution should be narrow because they would be condensing from volatilised anhydrous ferric chloride gas of known and modifiable initial atmospheric density (or partial pressure) and temperature. The weight per annum of ISA released in order to provide its part in cooling the GBR water might be estimated from the number of supplementary CCNs required to generate or thicken marine cloud over the area in question, once Seatomiser units had provided their own (second) sea salt aerosol (SSA) CCNs and humidification services, and once the additional (third) CCNs provided by iron-supplemented and phytoplankton-generated dimethyl sulphide (DMS) emissions had been estimated. The fourth method, surfactant-stabilised nanobubbles, involves bubble albedo which can be regarded as the similar, but inverse, of aerosol albedo. Now, the nanobubbles generated by the AnzaiMCS bubble diffusers are known to be of a narrow size range, which is likely to be controllable by varying the spinning rate of my hollow, disc diffusers using the hydrophobic, Anzai diffuser material. The rate of bubble formation is directly a function of the number of dispersal units, their air-pressurisation and rotational disc velocity. There was suggestion that nanobubbles might harm marine life. However, the reverse has been proven by nanobubbles restoring a polluted part of Tokyo Bay and by other demonstrations. A fifth method might be allowed in that the four would also contribute to the lessening of the harmful degree of sunlight intensity on coral that Daniel noted exacerbates the effect of elevated temperature on coral bleaching.

  

Challenge 3 is also addressed in multiple ways. First, the Aerostat/slurrypump/volatilisation method should require less high-cost fossil fuel energy than by using shipping or aircraft. Second, by using local, commercial wind turbine power to make aerosols or reflective, long-lived nanobubbles in the sea surface microlayer (SSML) intermittently as the wind blows and at the more productive times selected by AI and forecasting, should make best use of available energy. Third, in Buoyant Flake manufacture that increases solar reflection by phytoplankton and transforms much residual insolation into biomass and oxygen, the use of simple baking technology, solar pond heat, and waste that is already finely-divided and stored material is the opposite of energy-intensive intervention. Moreover, as the flake plumes on the sea surface require only annual renewal and bulk dissemination from obsolete shipping, the capital and energy costs of distribution are minimal. Fourth, the energy required to generate a microbubble in seawater several centimetres deep by this nanobubble method is thought to be close to the theoretical minimum - and they should last for months in the SSML, not just days for tropospheric aerosols. Fifth, customised, commercial, Seatomiser nozzles using internally-mixed, wide-aperture, much higher than usual, tri-phasic pressures (air, water and effervescence), with conditioning baffles to remove undesirably large seawater droplets, are likely to be better and more energy-efficient than are fine aperture spray nozzles. 

Challenge 4 Buoyant Flakes only require crewing for manufacture, bulk dissemination and probably some Measurement, Reporting and Verification activities. The other three methods typically require only maintenance and resupply crewing, some of which would be done by local staff from local bases. Such staff might well crew installations of more than one cooling method, thus making best use of their time, facilities and skills. 

Challenge 5 MCB by moving spray vessel, crewed or otherwise, is restricted to a minority of locations by local deficiency of humidity, of existing cloud cover, of weather conditions, and of time getting to and from, and staying in port. Such limitations are far less severe for my four methods. Daniel has suggested that anchored wind turbines would have to be moved out of the way from hurricanes. However, an AI Overview suggests that "Yes, anchored (floating) offshore wind turbines can be designed to withstand hurricane-force conditions. Key engineering and operational strategies are making this possible, including the adoption of specialized control systems, nature-inspired flexible blades, and resilient floating platforms."

Challenge 6 MCB and Buoyant Flake transporting vessels are likely to be powered by fossil fuels for some time yet. However, the other three alternative cooling methods proposed are mainly to be powered by renewable wind energy, possibly some of which might be stored in backup batteries, as locally-generated electrolytic hydrogen, or in graphene supercapacitors, or be used for water desalination.

Your thoughts, please.

Sev Clarke

[Brian Cady]

A side note: Sev, I'm intrigued with gaseous ferric chloride, and see its boiling point is around 315Celsius. As only trace quantities are needed to precipitate into aerosols, and as the gas seems to me to be a workable source to form aerosols of designed size, this seems promising.

OTEC (Ocean Thermal Energy Conversion) plants use slight (+-20C) temperature differences between hot, tropical surface and cold, deep (+1km) worldwide bottom water to drive turbines, capturing usable power typically as electricity.

Carnot's law limits overall OTEC efficiency, mandating enormous water flows to power OTEC plants per power unit put out. On the other hand, as OTEC plants are typically on the ocean surface, the massive cool water flows brought near the surface might cool coral reefs while yielding a little electrical power.

OTEC plants need deep water access. Perhaps they could be operated up-current from coral reefs in deep water, so that:

1. the OTEC plants can get both deep, cold and surface, hot waters,

2. The cooled surface waters can mix with other surface waters as together these approach the coral, to avoid cold water extremes impacting coral severely.

As OTEC plants also need much hot surface water. ship-mounted OTEC plants situated in surface water currents could access a flow of hot surface water.

Some designs avoid metal heat exchangers that are expensive to buy and clean by running an 'open-cycle' design, in which a vacuum is drawn above hot surface water, boiling them - the 'steam/vapor' flows to a chamber within which sprayed cold deep water condences that steam/vapor. This induces a large rapid flow of salty vapor from the first chamber to the second, which might best be tapped through Bernoulli-effect venturi, as a turbine in this salty flow would be quickly encrusted with corrosive salt, versus the vacuum flow to the venturi being clean of salt and such.

The meager power generated could assist electronic reef-building or other efforts.

Brian

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[Sev Clarke]

Brian,

It does indeed seem promising. Furthermore, ultra-fine misting machines run at high pressures can produce seawater droplets of diameter around 12𝜇𝑚. Let us assume this can be brought down to 10𝜇𝑚 by specialist nozzles running at higher pressures. Now, a 10𝜇𝑚 diameter, cloud condensation nucleus (CCN) sphere of seawater weighs ~5.37x10^^-13kg and the 3.5% salt in it that produces a sea salt aerosol CCN would weigh approximately 1.9x10^^-14kg. Whereas a CCN made from a 30nm diameter sphere of ferric chloride (generated by volatilising the ferric chloride salt and letting it condense in air, as my AMRAerostat method suggests) would weigh approximately 4.10x10^^-20kg.

Therefore, some 4.6x10^^5 or 460,000 times more CCNs would be produced by using ferric chloride than the same weight of sodium chloride from seawater - with the added benefits that it would photocatalytically destroy tropospheric methane and ozone more effectively and contribute to generating more phytoplankton and their DMS CCNs. 

I surmise that volatilising enough ferric chloride CCNs to offset their dearth in the Coral Sea, and thus to help save the GBR by MCB and related means, might indeed be a practical, safe and economical solution. 

Regarding OTEC, I am not a proponent of such a solution to save coral reefs for mainly four reasons:

• moving surface ocean heat lower makes the overheating problem much worse for later generations
• due to the low temperature differences between tropical surface water and deep ocean being so low, the power generated is not done efficiently
• slightly-warmed, dense and possibly nutriated water from the deep would probably not spread widely over the warm surface but soon sink back to the depths, thereby reaching few coral reefs
• the capital and maintenance costs of OTEC facilities would be exorbitant

Sev

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[Sev Clarke]

Hi John,

See my comments in bold below.

On 18 May 2026, at 9:10 pm, John Macdonald <ning...@icloud.com> wrote:

Hi Sev 

Some further thoughts to your 6 challenges (in response to Daniel Harrison’s excellent presentation).

Willis Island, an Australian Meteorological base in the Coral sea could also be used for fixed pilot testing of both MCB and ocean whitening, upwind and up-current of the GBR. New Caledonia could certainly offer a ‘long frontage’ of MCB dispersion beyond the reef. Yes, but there are also many other potential sites. The islands could be used for bases, the shallow waters nearby for anchored wind turbines and other infrastructure. Jobs would be available for islanders and spare power from the wind turbines might be made available to villages and local industry.

A hybrid mix of nanobubbles (for longevity) and  microbubbles (for added reflectivity) might deliver optimum results for ocean whitening. Ansai’s MCS bubble diffusers and your spinning discs are very promising. I am also hopeful that my atomising convergent/divergent anti fouling nozzle will delver similar results. Both sizes of bubble are thought to have about the same albedo.

Localised reef cooling could also be delivered by Bright Buoy solar thermal nanobubble generators for ocean whitening and MCB. These low cost, unmanned devices are fully autonomous and moored on sandy sea floors up-current of coral atolls to cool the immediate water surface. Each device could cool up to 1 km2 at optimum solar flux(TBC). In the event of a cyclone, these inflated devices can be deflated to escape wind and wave damage. With demonstrated safety, hopefully GBRMPA will permit. All such local cooling means should be considered

Regional cooling could also be scaled up by retrofitting commercial ships with containerised plant that use the waste heat from ships’ engines to generate CCN for MCB and nanobubbles for ocean whitening. A persuasive business case for shipping operators is nanobubble hull lubrication which reduces fuel consumption - 10-15%

based on trial testing. At any time, hundreds of ships that could deliver regional cooling, traverse the east coast of Australia outside the GBR. In my opinion, this could be the most effective way to cool the GBR.

In addition to your buoyant flakes, biosurfactant concentrate to increase bubble life can be extracted directly from the ocean surface. But why not use it in situ to stabilise Anzai nanobubbles which could then be carried by currents across the Coral Sea to the GBR - no ships or crews required? This process uses a heated separation plate (also using ship surplus heat energy) to collect surface active foams drawn from the upper 200-500mm of the sea surface.

John

On 16 May 2026, at 3:43 PM, 'Sev Clarke' via Healthy Planet Action Coalition (HPAC) <healthy-planet-...@googlegroups.com> wrote:

Colleagues,

Dr. Daniel Harrison’s recent presentation to HPAC, see https://healthyplanetaction.org/guest-speakers/  on how marine cloud brightening (MCB) might save the Great Barrier Reef (GBR) was both excellent and well-received. At the latter part of the discussion that followed, I itemised six of the challenges his proposed method had yet to overcome before it could become practical. These were that:

1. the seawater droplet or sea salt aerosol particle size distribution achieved was still sub-optimal
2. the rate of droplet formation was insufficient (by some two orders of magnitude, 10^^15 not 10^^17/sec)
3. the production was too energy intensive to be used at scale. (Daniel said it had to be reduced some 30-fold)
4. using crewed ships as the delivery platforms is too expensive
5. the method requires such restrictive conditions of humidity, existing cloud cover, and cloud condensation nuclei (CCN) density as to render it of doubtful practical value, and
6. being powered by fossil-fuel, rather than renewable energy, makes it problematic.

Furthermore, it is submitted that if the huge volume of the top few to several metres of ocean water over the GBR is to be cooled sufficiently to bring back the coral, then the cooling and shading of the over-warm water in and entering the Reef is likely to be needed long before and also far upwind and up-current (it flows West at 20°S onto the GBR where it splits N and S) of the Reef itself. Indeed, that ocean cooling by reflective aerosol, cloud or surface water solar reflection would probably need to take place over thousands of kilometres distant, perhaps as far afield as the Melanesian islands of Fiji (3,000km E and 15°S) or New Caledonia (1,700km E and 22°S), and possibly further.  It should be noted that the prevailing winds from Coral Sea+ islands upwind of the GBR typically bring cooling cloud to the GBR. 

Such cooling might be achieved using combinations of my four, proposed, climate restoration methods: Buoyant Flakes, Nanobubbles, Seatomisers and AMRAerostats. 

 

Challenges 1 & 2 are addressed in five ways. The first is by Atmospheric Methane Removal Aerostats which would release 20-50nm (av. ~30nm) diameter iron salt aerosols (ISA) of ferric chloride over the ocean, typically from off-island installations, at altitudes from 500-2,000m. The aerosol particle size distribution should be narrow because they would be condensing from volatilised anhydrous ferric chloride gas of known and modifiable initial atmospheric density (or partial pressure) and temperature. The weight per annum of ISA released in order to provide its part in cooling the GBR water might be estimated from the number of supplementary CCNs required to generate or thicken marine cloud over the area in question, once Seatomiser units had provided their own (second) sea salt aerosol (SSA) CCNs and humidification services, and once the additional (third) CCNs provided by iron-supplemented and phytoplankton-generated dimethyl sulphide (DMS) emissions had been estimated. The fourth method, surfactant-stabilised nanobubbles, involves bubble albedo which can be regarded as the similar, but inverse, of aerosol albedo. Now, the nanobubbles generated by the AnzaiMCS bubble diffusers are known to be of a narrow size range, which is likely to be controllable by varying the spinning rate of my hollow, disc diffusers using the hydrophobic, Anzai diffuser material. The rate of bubble formation is directly a function of the number of dispersal units, their air-pressurisation and rotational disc velocity. There was suggestion that nanobubbles might harm marine life. However, the reverse has been proven by nanobubbles restoring a polluted part of Tokyo Bay and by other demonstrations. A fifth method might be allowed in that the four would also contribute to the lessening of the harmful degree of sunlight intensity on coral that Daniel noted exacerbates the effect of elevated temperature on coral bleaching.

  

Challenge 3 is also addressed in multiple ways. First, the Aerostat/slurrypump/volatilisation method should require less high-cost fossil fuel energy than by using shipping or aircraft. Second, by using local, commercial wind turbine power to make aerosols or reflective, long-lived nanobubbles in the sea surface microlayer (SSML) intermittently as the wind blows and at the more productive times selected by AI and forecasting, should make best use of available energy. Third, in Buoyant Flake manufacture that increases solar reflection by phytoplankton and transforms much residual insolation into biomass and oxygen, the use of simple baking technology, solar pond heat, and waste that is already finely-divided and stored material is the opposite of energy-intensive intervention. Moreover, as the flake plumes on the sea surface require only annual renewal and bulk dissemination from obsolete shipping, the capital and energy costs of distribution are minimal. Fourth, the energy required to generate a microbubble in seawater several centimetres deep by this nanobubble method is thought to be close to the theoretical minimum - and they should last for months in the SSML, not just days for tropospheric aerosols. Fifth, customised, commercial, Seatomiser nozzles using internally-mixed, wide-aperture, much higher than usual, tri-phasic pressures (air, water and effervescence), with conditioning baffles to remove undesirably large seawater droplets, are likely to be better and more energy-efficient than are fine aperture spray nozzles. 

Challenge 4 Buoyant Flakes only require crewing for manufacture, bulk dissemination and probably some Measurement, Reporting and Verification activities. The other three methods typically require only maintenance and resupply crewing, some of which would be done by local staff from local bases. Such staff might well crew installations of more than one cooling method, thus making best use of their time, facilities and skills. biosurfactants directly from the ocean surface

[Sev Clarke]

Thanks, Dan, for this paper. I see that much good work has already been done.

Regarding the ISA volatilisation method, would any of your team be prepared to measure how close to optimal is the particle size distribution that could be achieved in the lab? Also, would your team’s modelling capabilities extend to modelling a year long near-sufficiency of tropospheric CCNs in the Coral Sea to their cooling effect on the SST of the GBR, as this might well be achievable in practice? Field testing might be compassed analogous to photographing a cloudy ship track using an island-based volatiliser.

Do you have any questions or doubts concerning any of the intervention methods I propose which I might attempt to answer?

Sev

On 19 May 2026, at 12:45 pm, Daniel Harrison <Daniel....@scu.edu.au> wrote:

Hi Sev, 

Actual numerical modelling regarding the relationship between net radiative flux change and the resulting adjustments in SST are presented in Harrison et al. ( 2019). 

https://gbrrestoration.org/wp-content/uploads/2020/09/T14-Environmental-Modelling-of-Large-Scale-SRM_v3.03-3.pdf

Dan

Daniel P Harrison

Associate Professor

Reefs and Oceans Research Cluster

National Marine Science Centre

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Honorary Associate  | School of Geosciences | University of Sydney       

Senior Research Fellow  | Sydney Institute of Marine Science

 

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[Paul Klinkman]

Dear Action Committee,

I approach the barrier reef cooling challenges with somewhat similar hardware but with a radical philosophy. As designed, your mister buoy arrays are likely to blunder like an elephant right through my philosophy, with unexpected consequences for your prototypes. You'd better hear me out.

The tropical ocean is going to have days of dry, descending air and other days of pop-up rain showers. My low-powered solar panel driven mister buoys aren't going to produce salt particles with small nuclei, but they will produce fog droplets that evaporate some of their water, which cools that fog droplet, and then the rest of the cooled water droplet descends back into the ocean and cools that tiny section of ocean next to the mister buoy. The area specifically downwind 100 meters from the mister buoy is covered with fog all day. This loss of sunlight and the swamp cooling effect cools that refuge for corals and related species to survive a bleaching event, and then the corals can start to repopulate the nearby bleached areas. Isn't creating small refuges a target?

I see three major impacts of H2O in the atmosphere. First, H2O is a greenhouse gas. Second, H2O creates cloud cover. Third, H2O often creates a vast vertical transfer of thermal heat. The vertical transfer of thermal heat above the majority of earth's greenhouse layer is king.

In a category 5 hurricane this third effect can be incredibly destructive. Therefore, watch the forecasts and turn the misters off at critical times so that you're not feeding the hurricane with extra water vapor. Rather, you're cooling the ocean on 90% of the days.

Know exactly how moist air from the sea's surface turns into updrafts that can be gobbled up by rain showers. This turns showers into larger thunderclouds. Given any standard temperature and pressure, moist air rises. Dry air descends and then slides in below to take the moist air's place. The mass of a mole of H2O molecules is less than the mass of a mole of N2 and O2 molecules, says your chemistry teacher. Heavier air drops. Lighter air rises. You could in theory put extra moisture into a hot air balloon for slightly better lift.

One potential problem is having near-100% humidity right next to the ocean in a flat layer and then less humidity with altitude. No big updraft of humid air gets going. As an updraft starter, I could see one or more buoys that put solar heat into an underwater tank of hotter water. Whenever this hotter water is sprayed into the air, a volume of super-moist heated air is created. This rises and breaks the plane. All of the surrounding moist sea-level air is pulled upward with the initial updraft.

If this updraft reaches two thresholds, we have a rain shower. First, we need condensation, a cloud on top. Second, when raindrops start to fall they create negative ions and negative ions cause cloud fog particles to be attracted to each other, which creates more rain. The second threshold is easily solved by spraying electrons near or into the super-moist air column. This puts a useful charge in the atmospheric air.

If a thundercloud gets going, it makes its own weather. Surface winds often blow in the direction of the thundercloud. As they blow, they gather extra moisture off of the sea surface, and then they take that moisture in the continuous updraft that feeds the thundershower. Rain causes lightning and lightning causes cloud fog particles to be attracted to each other.

So, my way to launch a thundercloud or to enhance an existing shower above the Great Barrier Reef is first to deploy an array of mister buoys that humidify the near-earth atmosphere. Second, pre-heat water to be sprayed, to create an artificial updraft in the middle of the moistened surface air that creates an updraft or that enhances an existing updraft. Third, add electrons to charge the local atmosphere.

Clouds and updrafts move with the trade winds. Get the array of mister buoys and hot mist buoys lined up for the next day's trade winds. Pick an existing cloud or cloud line to feed as it goes by, or pick a specific cloud launch time. At that time, expend the hot mist out of the central hot mist buoys.

The result is more cloud cover, more sea-cooling surface winds beneath the thundershowers and more heat transfer straight up, with cold rain or even hail in more temperate zones coming back down to the surface.

I could see ten meter high sails deployed on buoys to the left and right of the buoys as seen in the trade wind direction. The relatively dry surface trade winds are pushed by the sails toward converging underneath the moist air, artificially goosing the moist updraft.

My cooling philosophy doesn't need microscopic salty droplets and it uses locally available wind and solar. My energy system then feeds itself on the sea's natural solar-driven heat for a multiplier effect after a thundercloud is started or fed.

I'm an open-source public interest inventor. A sketch of my inexpensive mister buoy can be found on my self-named website at https://klinkmansolar.com/knightfog.htm#U4d

Yours in Hope,

Paul Klinkman

[Tom Goreau]

Great ideas, Paul, I hope you get the funding to test them!

 

Best wishes,

Tom

 

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[Sev Clarke]

Dan,

Following up on this discussion, presumably you are aware of the benefits that might be derived from making CCNs smaller than those derived by spraying seawater. Now, a kilogram/second of ferric chloride, vaporized by such as my AMRAerostat method, when/if condensed into 30nm diameter nanoparticulates each of approximately 4.1x10^^-20kg weight, would form one of 2.4x10^^19 CCNs, which is 240 times the 10^^17 CCN/sec that you say is required to be a useful contribution to cooling the GBR. Furthermore, a single Aerostat should be capable of having pumped to it a kg/sec of FeCl3 salt in bio-oil slurry. 

What is now desirable is to test the cloud formation capabilities of such an ISA plume in the environs of first the lab and then the Coral Sea.

Sev

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