On Rising Seas: Groundwater Discharge, the Missing Factor

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H. Sterling Burnett

Managing Editor, Environment & Climate News at The Heartland Institute

H. Sterling Burnett, Ph.D. is managing editor of Environment & Climate News and a research fellow for environment and energy policy at The Heartland Institute. Burnett worked at the National Center for Policy Analysis for 18 years, most recently as a senior fellow in charge of NCPA’s environmental policy program. He has held various positions in professional and public policy organizations, including serving as a member of the Environment and Natural Resources Task Force in the Texas Comptroller’s e-Texas commission.

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Jim Steele, author of Landscapes and Cycles, published a new paper on Climate Etc. arguing groundwater discharge into the oceans is contributing to sea level rise. This is a missing factor unaccounted for by climate models. Once properly accounted for, the amount of sea level rise attributable to anthropogenic warming is much less than climate models estimate. The Intergovernmental Panel on Climate Change (IPCC) acknowledges it cannot account for as much as 25 percent of the sea level rise. The IPCC’s 2002 report stated, “the historic rise started too early, has too linear a trend, and is too large.”

Groundwater slowly discharges into the oceans over time, with the rate and amount varying dependent on periodic shifts in ocean currents, rainfall amounts, and rates of aquifer recharge, among other factors. Climate models do not take into account groundwater discharge into the world’s oceans, yet the volume of fresh water stored as groundwater is second only to the amount of water frozen in Antarctica’s icy expanse, and it is three to eight times the amount of water contained in Greenland’s glaciers.

On relatively short time scales, during periods of frequent La Niñas, a greater proportion of precipitation falls on the land globally “and when routed through more slowly discharging aquifers, sea level rise decelerates. During periods of more frequent El Niños, more rain falls back onto the oceans, and sea level rise accelerates. In contrast to La Niña induced shallow-aquifer effects, deep aquifers have been filled with meltwater from the last Ice Age, and that water is slowly and steadily seeping back into the oceans today,” writes Steele.

As Steele explains in detail, deep aquifers are constantly discharging water into oceans, and “primarily regulated by geological pore spaces (in addition to pressure heads), the slow and steady discharge of these older waters affects sea level rise on century and millennial timeframes.” This discharge could account for a large portion of, if not all, unaccounted-for sea level rise.

Until climate models account for the volume of water the world’s shallow and deep aquifers discharge into the oceans, the amount of sea level rise they attribute to human causes should be considered inaccurate.