By Alex Laplaza
Looking back to Earth's climatic past depicts a bleak future for coastlines worldwide. Two major climate studies published late March do just that. The first, published by an influential group of scientists led by former NASA scientist James Hansen, suggests the impacts of greenhouse gas emissions will be quicker and far more catastrophic than originally envisioned. The second, published in acclaimed journal Nature, nearly doubles current projections of sea level rise by 2100 due to rapid disintegration of Antarctic ice sheets.
Although the studies differ in scope and subject, parallels between the two are evident. Both suggest we have vastly underestimated both the short-term and long-term impacts of sea level rise. Drawing on evidence from both ancient climate change, or “paleo-climatology” and sophisticated computer models, the two studies suggest sea levels could likely drown the world’s coastlines within the next 50 to 100 years – an increase previously estimated to take multiple centuries at the very least. Although differing in exact metrics, the two studies’ estimates of short-term (next century) sea level rise roughly double the plausible worst-case scenario of the United Nation’s Intergovernmental Panel on Climate Change (IPCC)
The first study, produced by nineteen highly influential climate scientists, applies evidence from previous climatic shifts, modern observation, and sophisticated computer models. Although the study’s title indicates rather passively that “2°C global warming could be dangerous,” its findings suggest a far more catastrophic scenario. The study’s main premise is that heat-trapping greenhouse gas emissions will provoke a much more abrupt climate shift than previously predicted. This shift would bring exponentially increasing disintegration of polar ice sheets. This is illustrated most clearly by the description of the immense and rapid melting of Antarctica and Greenland – a scenario that has grave consequences beyond merely raising sea levels.
One such consequence is known as “polar ocean stratification.” When cold, fresh meltwater runs off melting land ice and pours into the oceans, thermodynamics trap the cold water atop a warmer ocean layer. The warmer ocean water reaches the base of ice sheets that sit below sea level, melting them from below. This temperature division, or “stratification,” sets off a dangerous feedback loop that could continuously promote the rapid disintegration of Greenland and Antarctica’s massive ice sheets described above.
This, in turn, causes cooling of the North Atlantic Ocean, even as overall planetary warming creates a warmer equatorial region. Such a North-South divide could drive more intense cyclones and harsh oceanic waves capable of severely eroding coastlines and cripple entire coastal cities.
The second study, produced by Robert DeConto of the University of Massachusetts - Amherst, and David Pollard of the Pennsylvania State University, focuses on Antarctic melting’s contribution to sea level rise. The study, like the first, is based on an improved understanding of previous warm eras in Earth’s history that featured much higher seas. Highly advanced computer models of Antarctica’s historical ice melt allowed the researchers to project near and long-term sea level rise.
The results were that a very high-carbon emissions scenario, such as the one we’re currently in, would cause nearly 4 feet of sea level rise by 2100 from melting Antarctic ice alone. The same model projects over a 50 feet rise by 2500. A moderate emissions scenario would cause Antarctica to contribute nearly two feet by 2100 and close to 20 by 2500. According to the study’s authors, this projection nearly doubles prior estimates of sea level rise, which had relied on a minimal contribution from Antarctica.
These grim projections are particularly bad news for U.S. coasts. Gravity normally pulls ocean waters toward Antarctica’s large mass. When the continent rapidly loses significant mass, the seas surge back toward the opposite end of the world. The consequence is that sea level rise is felt unevenly across Earth’s coastlines. Northeast U.S. coastlines will see much of this sea surge. Low-lying cities such as New York and Boston are likely to suffer severely as a result.
The two studies share a bleak view of the future of our coastlines, however, equally notable is their fear of the past. Both studies draw from ancient climatic evidence of the last interglacial period of Earth’s climate history, the Eemian period. This period, between 115,000 and 130,000 years ago, was only slightly warmer than today, but featured a sea level estimated to be nearly 20 to 30 feet higher than current levels. An improved understanding of this period reveals particularly dire ideas about polar melting, rising seas, the shutdown of ocean circulations, and increased incidence and severity of storms. The fear is that we may be creating our own Eemian period.
In other words, by overlaying the past and the present, the two studies provoke troubling questions and forecasts of the future.
For more information, contact Alex Laplaza at firstname.lastname@example.org.