Can sea level rise be slowed? A new project called Sea Level Investigation and Management (SLIM), made possible by a generous gift from Cornelius “Neil” Prior Jr. LLB ’62, aims to find out.

More than 250 million people currently live within two meters of sea level, and the risk of coastal flooding is increasing as sea level rises by an average of more than three millimeters a year. Most of this rise is a consequence of anthropogenic greenhouse gas emission, where global warming causes the volume of the ocean to thermally expand and ice to melt and run off into the ocean.

About 10 percent of sea level rise, however, is caused by another set of human activities: overpumping of aquifers. Peter Huybers, chair of the Department of Earth and Planetary Sciences and the leader of SLIM, will investigate if flipping the balance between aquifer recharge and withdrawal to instead sequester water on land could slow sea level rise significantly.

“There may be a win-win here where we can help to stabilize and recharge aquifers and help to globally mitigate risks of coastal flooding,” said Huybers.

Another indication that sea level can be slowed by retaining more water on land comes from the fact that sea level declined in 2011 when La Niña in the Equatorial Pacific caused increased rainfall over land areas such as the interior of Australia, where there is an extended period of time for water to flow back into the ocean.

SLIM will convene a group of scientists and engineers to explore whether geotechnical approaches (mitigating “wedges”) can be deployed to slow sea level rise.

One well-recognized sea level wedge is to reduce greenhouse gas emissions. However, the rate of sea level rise over the coming decades is largely insensitive to different emissions pathways. The central estimates of rates of sea level rise to 2050 only change by one millimeter per year between the lowest and highest emissions scenarios considered by the Intergovernmental Panel on Climate Change in their most recent report.

Another potential sea level wedge is to reduce overpumping of aquifers by, for example, improving the efficiency of agricultural irrigation systems. The complement of limiting overpumping is to increase aquifer recharge. Recharge can be increased through capturing runoff and allowing for infiltration, as well as by direct injection of water into aquifer systems. Stabilizing aquifers is also relevant for averting compaction of aquifer systems that, in the case of coastal areas, can lead to heightened rates of local sea level rise.

Another wedge may come from filling surface depressions. For example, various inland seas are shrinking—including the Aral, Caspian, and Dead Seas—suggesting an opportunity to pump seawater into these regions to stabilize and replenish their levels. Another notion is to fill dry basins, such as the Qattara Depression, a project that was considered by Egypt in the 1970s for purposes of hydropower production and farming.

These concepts are technically challenging due to the massive volumes of water involved. Also complex are the societal trade-offs.

“It has to be considered from the outset that modifying surface and subsurface reservoirs for the purposes of abating coastal flooding might involve difficult trade-offs,” says Huybers, a professor of earth and planetary sciences and of environmental science and engineering.

SLIM will involve experts in policy and ethics in their research, recognizing that this is but a first step in the fuller consideration of the feasibility of deploying any sea level management approach.

Several years ago, donor Neil Prior became concerned that rising sea levels caused by climate change in places like Venice, Miami, and Bangladesh were being neglected compared to the enormous political and financial resources focused on fossil fuels. Prior said, “I created a small nonprofit organization to engage science and research in finding cost-effective solutions. After several false starts, I was introduced to Professor Huybers, who shared my interest in and concern for the problem.”

Prior connected with Huybers through the Harvard University Center for the Environment, a center of the Salata Institute, and presented a challenge: to consider how one millimeter of sea level rise could be averted annually through sequestering water on land.

“At first, I was skeptical that anything useful could be done with respect to actively managing sea level rise,” said Huybers. “But after studying the problem for a while, I think sea level management merits serious consideration.”

Prior said, "My hope is that Professor Huybers’ findings will be broadly applicable and, by raising awareness, lead to solutions for the problem of rising sea level.”

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