Using a newly available estimate of damages from global warming and a measurement of Earth’s energy imbalance, the economic value of placing solar reflective covers over water reservoirs to cool the planet, reduce evaporation, and reduce maintenance costs has been published. In places where the cost of making a pond white with salt is low and it is usually sunny, the value of the benefits exceeds the cost.
In 2020,Stefania Bonafoni and Aliihsan Sekertekin demonstrated that albedo (solar reflectivity) of surfaces with a minimum dimension of about 40 meters can be determined using data from satellite images. In 2022,Smoliak et al. showed that the potential amount of sunlight that could theoretically be reflected by the surface back to space from any location by a reflector that sends reflections in all upward directions can be estimated using model data. Thus, we can calculate the increased number of megawatts reflected to space by each white salt pan compared to what would otherwise be there averaged over one year -- the number of Reflected Megawatt Years (ReMYs).
In 2023, James E Hansen et al. reported that Earth’s mean energy imbalance was 587 million megawatts. Ideally, we would reflect to space enough solar energy to bring this imbalance to zero and an additional 10% or so beyond achieving balance so the Earth begins to cool, a total of about 650 million megawatts. van der Wijst et al.(2023) estimated that projected additional warming would likely cost the world economy about 0.5% of its gross domestic product in 2025. If, by 2025 we could spend less than 0.5% of annual world GDP and thereby send to space 650 million megawatts, that would be cost-beneficial, considering only the economic benefits without also considering other damages and risks such as biodiversity losses, health, and tipping points.
The World GDP in 2025 is projected to be about 116 trillion US dollars. Thus, reflectivity interventions that reflect650 million megawatts to space would provide an average benefit in 2025 ofUS$780 per Reflected Megawatt Year (ReMY). However, the marginal value of the first tranche of Reflected Megawatt Years (ReMYs) is higher than the average value. As warming goes down and switches to cooling, the marginal benefit of an additional ReMY will go down and the value of the last ReMY will be virtually zero. Assuming that the decline in marginal value is linear, because the last ReMY will have zero value, the first ReMY will have a value double the average and therefore $1560.
Estimated economic value of white salt where in recent times there is dark sand or water
Shallow coasts of oceans and land-locked salty lakes have for millennia been dammed to form shallow lagoons that can be flooded and then shut off from the sea so the water will evaporate and leave behind a white layer of salt. Historically, the purpose is simply to harvest the salt. There are shallow lagoons that were formerly so used but are no longer because it is not presently cost-effective for producing commercially valuable salt. These lagoons are typically left full of shallow water or dark mud.
Dark lagoons that have not been kept white with a layer of salt in recent years can be converted to highly reflective white surfaces at small cost for high reflected megawatt gains. Using satellite data, reflectivity of the lagoon can be verified multiple times each year to generate an accurate annual average of megawatts gained, and the area of each lagoon can be determined by satellite.
If the present solar reflectivity of a no-longer-used salt pond is 7% and it is boosted to 40%, this would gain 33% of the potential reflectivity. Where the potential is 145 watts per square meter, such as the Great Salt Lake, the gain of converting one square kilometer would be 48 megawatts for a value of about (x $1560 =) $75,000 per year. This is far more than the cost to convert the pond to white salt and maintain it. Of course, competing uses such as for wildlife need to be balanced.
Lakes that are salty and drying up can be managed to ensure the exposed beds are covered with highly reflective salt by creating lagoons with mud berms and pumping saltwater into them. Large areas could be so converted from 27% to 47% around the Salton Sea which has a reflectivity potential of 181 watts per square meter. The gain would be 36 megawatts per square kilometer and the salt crust on top should seal in dust so it does not blow in the wind which is a present problem. The shores of the Dead Sea can be converted from a reflectivity of 11% to a reflectivity of 61%, a gain of 50% of 162 watts per square meter for a value of $126,000 per year per square kilometer. The muddy shores of Lake Poopó in Bolivia, with an area of 27,000 square kilometers (10,000 square miles) have a reflectivity potential of 211 watts per square meter. Being mostly dry and dusty, most of these shores have no significant alternative uses.
Desalination plants take in salty sea water, extract fresh water, and discharge a brine of highly concentrated salt water. Instead of discharging salty brine into adjoining seas which causes environmental harm, desalination plants can discharge brine into multiple evaporation ponds, one pond at a time so that most of them are white with dried salt most of the time. The increased number of megawatts reflected to space can be determined to provide a subsidy to encourage creating evaporation ponds for each desalination plant and reduce environmental harm.