Lasting coastal hazards from past greenhouse gas emissions

The emission of greenhouse gases into Earth’s atmosphere is a by-product of modern marvels such as the production of vast amounts of energy, heating and cooling inhospitable environments to be amenable to human existence, and traveling great distances faster than our saddle-sore ancestors ever dreamed possible. However, these luxuries come at a price: climate changes in the form of severe droughts, extreme precipitation and temperatures, increased frequency of flooding in coastal cities, global warming, and sea-level rise (1, 2). Rising seas pose a severe risk to coastal areas across the globe, with billions of US dollars in assets at risk and about 10% of the world’s population living within 10 m of sea level (3⇓–5). The price of our emissions is not felt immediately throughout the entire climate system, however, because processes such as ice sheet melt and the expansion of warming ocean water act over the course of centuries. Thus, even if all greenhouse gas emissions immediately ceased, our past emissions have already “locked in” some amount of continued global warming and sea-level rise. In PNAS, Nauels et al. (6) examine how greenhouse gas emissions since 1750, and anticipated future emissions, contribute to global sea-level rise. They find that emissions from 1750 to 1991 have committed us to about 60 cm of additional sea-level rise by the year 2300, relative to the mean from 1986 to 2005, with another 24 cm stemming from greenhouse gases emitted between 1991 and 2016. So, through our emissions thus far in modern human history, we have committed to a total sea-level rise of about 84 cm over the next couple of centuries. This is the price we pay for the luxury of about 200 y of relatively unchecked greenhouse gas emissions. To be clear, past emissions have already been … [↵][1]1Email: aewsma{at}rit.edu. [1]: #xref-corresp-1-1