One of the most concerning aspects of global warming is the potential for rising seas to damage infrastructure and property and displace a large proportion of our planet’s population. Since 1993, sea level has increased an average of 3.4 millimeters per year—more than twice as fast as the rate over the first 9 decades of the 20th century.
When projecting future sea levels, scientists have traditionally relied upon physical models and expert assessments to project the polar ice sheets’ response to various emission scenarios. These approaches, however, haven’t taken into account some physical processes that can quickly increase ice sheet discharge, such as the collapse of terminal ice cliffs and the breakup of floating ice shelves caused by a process known as hydrofracturing.
Now Kopp et al. have integrated both of these processes into a probability-based modeling framework to explore how they could affect future projections of global and local sea level changes. The results indicate that these mechanisms could significantly raise sea level forecasts for high-emission scenarios, including nearly doubling the median projections of 21st century global mean sea level rise by 2100.
Moreover, these mechanisms don’t fully kick in until the second half of the century, meaning that a global scenario leading to 50 centimeters of sea level rise over a century and one leading to 2 meters of rise won’t be distinguishable from continental-scale observations for decades to come. Reducing uncertainty will require developing a better, fine-scale understanding of ocean–ice sheet interactions. However, cutting emissions significantly affects the role these processes play: Sea level rise projections for a low-emissions scenario, consistent with the goals of the Paris Agreement, are close to unchanged by the inclusion of these mechanisms.
Because the researchers have not yet incorporated other important physical processes that could affect sea level into this model, such as the capacity of firn to buffer meltwater, they caution that this study does not provide unique statistical probabilities of future sea levels. Rather, it both offers a tool for exploring the sea level implications of polar ice sheets’ complex physical responses to global warming and highlights the deep uncertainty that characterizes sea level change in a high-emissions future. (Earth’s Future, https://doi.org/10.1002/2017EF000663, 2017)
—Terri Cook, Freelance Writer