Sea Level Rise Cut in Half?

Abstract

Sea level is expected to rise 20 cm by mid-century and over a meter by 2100 assuming a 2 °C rise in temperature. Global groundwater depletion (withdrawal greater than recharge) is between 145 and 189 km3/year and is added to the ocean. Groundwater depletion, in fact, contributes approximately 0.8 mm/year or about 25% of the current annual 3.1 mm to the rise; approximately 25% of rise is from melting glaciers and ice caps, and approximately 50% due to thermal expansion. Owing to this rise, much of the Earth's coastal infrastructure will be extensively stressed, potentially forcing relocation of millions of people. As it appears increasingly unlikely that all the nations of the world will coordinate action to reduce the greenhouse emissions responsible for climate change and subsequent sea level rise, one may wish to consider a geoengineering approach. We propose that ASR (aquifer storage and recovery), in which depleted aquifers are recharged by direct engineering intervention, can be used to delay sea level rise. In general, geoengineering seeks to control climate by either removing greenhouse gases from the atmosphere or reducing solar radiation. It may, however, also control specific impacts of climate change such as sea level rise while not addressing the fundamental cause. Such an adaptation strategy may delay some consequences of global climate change, giving governments, industries, and individuals additional time to reduce greenhouse gases and/or construct sea level rise resistant infrastructure. Surface water such as lakes, reservoirs, rivers, soil moisture, and atmosphere are in dynamic equilibrium with short residence times of a few days to weeks. Groundwater, glaciers, and ice caps, the other major freshwater reservoirs, have a much longer residence time of many years, decades, or even centuries and thus, provide opportunities for time-delay management. As globally many of the aquifers contributing to the annual groundwater depletion have been unsustainably developed for decades, there is significant dewatered aquifer volume available for more than annual withdrawals; thus, diverting additional runoff to aquifer storage could reduce the sea level rise to about half of the current value for decades. This time-delay strategy would give coastal communities time to reduce the risk associated with rising sea levels and importantly, provide needed water resources enhancement for many inland areas. Aquifer storage and recovery is a well-established water management technique that is, however, energy intensive owing to water collection, treatment, and transport; thus, engineered recharge is currently used only where the value of water or its impact is sufficiently high to justify the energy costs. If, however, some of the economic benefits of modifying sea level rise could flow to aquifer storage and recovery, then it could become a widespread water management tool while ameliorating sea level rise. For example, a modest tax credit for every cubic meter of water recharged would change the economics of many potential aquifer storage and recovery sites in the United States. One advantage of aquifer storage and recovery for depleted aquifers is that much of the aquifer engineering infrastructure (e.g., wells, piping, pumps, water treatment) already exists. Additionally, the potential aquifer volume is known, and the aquifers are well studied and modeled, thus reducing both capital and operating costs. There are numerous financial models for implementing the process, ranging from full government to full private with variable control of owning, designing, constructing, and operating such facilities. The economic benefits of this type of sea level control mechanism would be spatially distributed, rather than concentrated on coastal inhabitants, thus, making this technique politically more palatable rather than investing solely in ameliorating coastal impacts. The ASR process is site specific and thus allows local decisions and planning, has a minimum of legal, ethical, and security concerns, and can operate with or without sanctions or intervention from a world governing body.