WATER - Interactive: Short-Lived Pollutants and Sea Level Rise

By Climate Central

The article, "Mitigation of short-lived climate pollutants slows sea level rise", by Hu et al., is a collaboration between scientists at the National Center for Atmospheric Research (NCAR), Scripps Institution of Oceanography, and Climate Central, and examines how much the rate and amount of global sea level rise can be reduced by cutting emissions of carbon dioxide (CO2) and four short-lived climate pollutants (SLCP) - methane, tropospheric ozone, hydrofluorocarbons, and black carbon - by mid-century (2050) and in the long term (2100). These results are compared to a "Business As Usual" scenario and to mitigating CO2 only.

Population Benefitting From Action
State	SLCP-Only	CO2-Only	Combined
U.S. FL LA VA NY CA NJ TX SC NC MD MA GA DE WA MS CT AL RI ME OR NH PA D.C.	1,780,280 1,389,946 80,051 56,173 55,695 50,886 39,600 24,657 20,914 19,347 10,438 10,079 5,505 3,900 2,949 2,866 2,578 1,186 943 926 859 386 249 150	559,798 396,902 31,758 19,203 22,668 16,563 20,082 17,088 7,442 7,929 4,579 4,549 2,353 2,562 1,407 1,498 1,179 533 439 387 355 166 98 58	2,014,042 1,476,910 112,835 67319 76,717 90,071 53,664 27,973 24,349 26,574 14,308 13,389 7,655 4,737 3,845 3,409 3,947 1,543 1,294 1,258 1,174 559 306 205

The most important findings of the study are as follows:

• Immediate mitigation of SLCPs can reduce the rate of sea level rise by about 18 percent "with negligible effect from CO2 reduction before 2050." By 2100, cutting SLCPs can cut the annual rate of sea level rise by 24 percent, with CO2 providing an additional 24 percent reduction.
  
• Combined SLCP and CO2 reductions can cut the rate of sea level rise by 18 percent by 2050 and nearly 50 percent (from 2.1 to 1.1 cm per year) by the end of the century, while reducing actual sea level rise by 31 percent. SLCPs account for more than 70 percent of this reduction.
  
• SLCP mitigation acts faster than CO2 mitigation on a time scale of decades to a century, but mitigating CO2 remains critical to limiting the ultimate level of warming and its impacts beyond those time scales.
  
• Delaying SLCP mitigation until 2040 (25 years) will decrease the impact of CO2 and SLCP mitigation on sea level rise by a third (~30 percent), and will make it difficult if not impossible to keep warming under 2°C (3.6°F) by end of the century.

To estimate the state-level impact of these projected reductions in sea level rise, we took the central estimates of global sea level rise from the four scenarios - with the caveats that these have large uncertainties surrounding them - and applied them along the U.S. coastal topography to determine the risk of submersion under these four different futures. We then computed differences in population at risk based on the results.

By focusing on the differences under pairs of scenarios, one being business as usual, the other being one of the mitigation options, we highlight benefits of the different choices; curbing CO2 only, SLCP only, or both.

Florida has by far the greatest population at risk from sea level rise, and thus derives most of the benefit of any action to slow it. The estimates reflect only the population at risk from ambient sea level rise; they do not take into account storm surges that in the future would launch from higher seas.

These numbers should be taken as an index of gain/benefits rather than at face value. As the paper discusses, the sea level rise values are projections, subject to uncertainties. Additionally, the actual computations along the U.S. coast rely on estimates of people or assets at risk that carry errors themselves. And perhaps most significantly, these numbers represent current demographics, not the future. Projections of future population growth all show an intensification of development and an increase in the population living along the U.S. coasts.

http://www.climatecentral.org/news/interactive-short-lived-pollutants-