How to Stop Sea Level Rise

A Jonathan Swift take on geoengineering of the planet

Oct 19, 2023

A paper just out by some of my colleagues at the University of Colorado explores the possibilities for “converting atmospheric water vapor to deposited ice over Antarctica” with the goal of reducing sea level rise. That paper reminded me of a draft of a short paper I wrote back in 2015 on a similar topic, but which I abandoned in the turmoil associated with being investigated by Congress when I decided to take a hiatus from climate work.1

I recall that when I wrote the paper that I never actually decided if I was advancing a serious proposal or was instead poking some fun at geoengineering proposals, in a kind of Jonathan Swift manner. The new paper out this week suggests that some are taking the idea seriously, at least scientifically.

Regardless, here it is, fresh from the 2015 archives!

How to Stop Sea Level Rise

Introduction

One of the consequences of the accumulation of carbon dioxide in the atmosphere is an inexorable rise in sea levels. The Intergovernmental Panel on Climate Change AR5 projected that the worlds coasts could experience sea level rise of 30 to 80 cm by 2100, and higher values cannot be ruled out.[1] The U.S. Environmental Protection Agency projects global sea level rise of about 150 cm by 2100, which could be limited to 89 cm with aggressive reductions in greenhouse gas emissions.[2]

The costs of sea level rise have been projected to be as much as 9.3% of annual GDP in 2100 if no adaptive actions are taken, totaling hundreds of trillions of dollars (2005). If adaptive actions are taken then these annual costs are estimated to be between $12 and $71 billion, with an additional ~$10 to ~$80 billion in residual flood costs.[3]

Even under scenarios of aggressive greenhouse gas mitigation and/or adaptation, the global costs of sea level rise are expected to total tens to hundreds of billion dollars per year to 2100. This paper offers an idealized assessment of a simple approach to geoengineering sea level rise to a preferred level. The purpose of this discussion is to enlarge discussion over options for dealing with seal level rise and the costs and benefits of various response options.

Stopping Sea Level Rise Quantified

The surface area of the world’s oceans is 361,900,000 square kilometers (km²). Thus, every millimeter of rise in sea level equates to an increase in the volume of the world’s oceans of 361.9 km³.[4] This equates to a cube of water 7.1 km on a side. Since the early 1990s, global sea level has increased at an average annual rate of about 3.4 mm per year.[5]

Stopping sea level would thus require removing from the world’s oceans a volume of water equivalent to the annual volumetric increase in global oceans. How might this be done and where would the water be stored?

The option considered here is to convert sea water to ice at a location where oceans meet ice sheets and temperatures are cold enough to keep the ice frozen for a very long period of time. There are several locations that meet such a description around the world; however for purposes of this idealized discussion, I will consider Greenland as a repository for frozen sea water. What would it take in terms of area, energy and costs to reduce global ocean levels by one millimeter?

What to Do with 360 km³ of Sea Water?

Technologies to convert water into ice are widely used to create artificial snow for recreational skiing. To identify realistic estimates of the performance and costs of existing, off-the-shelf, snowmaking technologies I contacted TechnoAlpin, Inc., a global snowmaking company, who provided me with the information used in the calculations below.[6]

The cost to produce one acre-foot of snow (one foot of snow over one acre) ranges from about $500 to over $2,000, depending on location and input costs. To generate skiable snow requires between about 135,000 gallons of water to more than 300,000. Because skiable snow is not of concern in this paper, I will assume that 325,000 gallons of water (that is, one acre-foot of water) can be used to generate one acre-foot of ice/snow (hereafter just “snow”).[7]

Thus, at $500 per acre-foot, this equates to a cost of $400,000 to produce one meter depth of snow over one square kilometer.[8] This cost represents energy, labor, repairs and maintenance. Colder temperatures are associated with significantly greater efficiency.

North America has a total of more than 150,000 skiable acres.[9] Conservatively, about one third of this area, or about 200 km², is under snowmaking. To remove one millimeter of sea level requires making the equivalent of one meter of snow applied over 361,900 km² or 1,800 times the total area currently under snow making in North America. One the one hand, this is a huge area, on the other it would afford economies of scale that would all but certainly drive down the unit costs of snowmaking at an industrial scale. At the same time, the infrastructure and labor costs are likely to be higher in a remote region near the poles. Readers are free to utilize alternative cost assumptions to those presented here; the last section of this paper provides a wide range of cost alternatives.

Thus, at $500 per acre-foot the cost to remove one millimeter of sea level equates to about $150 billion dollars. If the costs of snow making at an industrial scale are cut by a factor of ten (a drop in price of 90%), then the cost of removing one millimeter of sea level rise would be $15 billion. For comparison, utility-scale solar energy dropped in cost by almost 75% (as compared to the cost of residential solar) for the decade ending in 2013.[10]

So is $15 Billion or $150 Billion a Lot to Reduce Sea level by 1 mm?

The answer to this question is that it depends. We can evaluate the magnitude of estimated costs to reduce sea level by one millimeter against several quantities.

In California, annual irrigation consumes about 35 cubic kilometers of water each year (>33 million acre-feet) over more than 32 km² of irrigated agricultural land.[11] This represents five times the volume of water required to reduce sea level by 1 mm. Put another way, reducing sea level by 5 mm requires moving the amount of water equivalent to the annual usage of water in California’s agricultural system. California’s irrigated land equals about 32,000 km². It would require more than 11 meters of artificially-produced snow over the equivalent area of Greenland (about 1.9% of the total area of the Greenland ice sheet) to reduce sea levels by 1 millimeter.[12]

On the one hand, producing 11 meters of snow over the areal extent of irrigated agriculture in California appears to be a huge task. At the same time, the California irrigation infrastructure exists and represents just a small fraction of the total infrastructure for irrigation globally, suggesting that the creation of such an infrastructure at such a scale is (obviously) well within possibility.

In addition, the reality of sea level implies the creation of a vast infrastructure along coasts around the world to protect against rising seas. These costs are estimated to be approximately $15 billion annually today, rising to more than $65 billion in 2100.[13] In addition, even with this vast infrastructure, annual flood costs due to sea level rise are estimated to be less than $10 billion today, potentially rising to more than $80 billion in 2100.[14] Thus, over the next 85 years the annual costs of sea level rise could range from about $25 billion today to more than $145 billion in 2100. If sea level rise is stopped, these costs would be avoided and thus would be a benefit.

Costs of eliminating SLR (billions USD) for various assumptions of snow-making costs and SLR rates. Pick your favorites.

Depending on the rate of sea level rise and the cost to remove sea water from the ocean, the benefits may or may not exceed costs of stopping sea level rise. The table above shows the annual costs of stopping sea level rise at $500, $50 and $5 per acre-foot of sea water. At $500 the annual costs far exceeds the benefits, at $50 the costs and benefits are very close to each other, and at $5 the benefits far outweigh the costs.

Some costs are not considered here, most notably initial infrastructure costs, which would necessarily include some source of energy supply. However, given that the cumulative costs over the next 85 years total is in the tens or hundreds trillions of dollars, for this simple analysis these costs can be assumed to be trivial in comparison. A more detailed rendering of the details of a Greenland snowmaking enterprise is unlikely to alter these first order results.

Conclusions

This idealized analysis presents a highly simplified way to look at the stopping of sea level rise by converting sea water into snow. Off-the-shelf technologies provide a starting point for analysis. The idealized analysis presented here finds that stopping sea level rise would require an effort comparable in scope to California’s agricultural irrigation infrastructure. Total costs are highly sensitive to the ability of an industrial-scale snowmaking infrastructure to realize economies of scale. This potential is of course unknown. However, at significant economies of scale stopping sea level rise by converting sea water to permanent ice sees benefits far exceed costs.

Whether geoengineering of this type is worth further exploring or even desirable in practice, if ultimately feasible, goes beyond the scope of this exploratory analysis. The analysis does provide an opportunity to open up discussion of sea level rise, its projected evolution, its impacts and alternative approaches to dealing with its consequences.

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