A new study finds that it is possible to greatly slow the rate of sea level rise, which is one of the biggest threats global warming poses, by cutting so-called 'short-lived climate pollutants', which warm the climate on timescales of a few weeks to a decade, in combination with reductions in long-lived greenhouse gases such as carbon dioxide.
The study, published in the journal Nature Climate Change, found that reducing emissions of these short-lived climate pollutants, including soot and methane, by 30 to 60 per cent by 2050 would slow the annual rate of sea level rise by about 18 per cent by 2050. Combining reductions in short-lived pollutants with decreasing CO2 emissions could cut the rate of sea level rise in half by 2100, from 0.82 inches to 0.43 inches per year, while reducing the total sea level rise by 31 per cent during the same period.
Related research by Climate Central scientists shows that the emissions reductions would potentially benefit more than two million Americans by 2100, who might otherwise be living below sea level at that point.
In addition, the study found that, compared to just cutting CO2 emissions, reducing the release of short-lived climate pollutants would do more to slow sea level rise before 2050, but that lowering CO2 emissions would be required to limit warming and warming-related impacts beyond that point.
“We need an all-of-the-above approach to controlling greenhouse gases. Clearly we need to cut CO2 emissions, but we also need to take advantage of the very substantial short term gains that can be achieved by cutting emissions of non-CO2 climate pollutants,” said Claudia Tebaldi, a research scientist at Climate Central and a co-author of the study.
As ocean waters warm and land-based ice sheets melt in response to manmade global warming, global sea levels have been rising by about 1.2 inches per decade, and recent studies project up to 1 metre of global sea level rise by the end of this century. This would imperil some of the world’s largest coastal population centers, including New York, Miami, and Mumbai. In the US, Florida has the greatest population at risk from sea level rise, with 2.1 million people projected to live below sea level in that state by 2100 if greenhouse gas emissions are not reduced.
Sea level rise will vary in different regions of the world due to ocean currents and movement of land masses, but this study examined global average sea level rise.
Already, sea level rise has made storm surge events more damaging than they otherwise would have been. In New York, for example, seas have risen by about one foot during the past century, which helped heighten the storm surge from Hurricane Sandy when the storm struck in October 2012. That storm killed more than 40 people in New York City itself, flooded all of the subway tunnels that connect Manhattan to Brooklyn and Queens, and cut power to lower Manhattan for days.
Carbon Dioxide Reductions Crucial For Addressing Long-Term Climate Change
Carbon dioxide emissions remain in the atmosphere for centuries, which makes it the most important greenhouse gas to reduce in order to limit long term climate change, but for the first time, this new study showed that cutting short-lived pollutants can also ease some impacts during the next few decades.
Previous work has examined the overall warming influence of short-lived pollutants and found that cutting the four key pollutants – black carbon (soot), methane, tropospheric ozone, and hydrofluorocarbons, also known as HFCs – can offset warming temperatures by up to 50 per cent by 2050. These pollutants are emitted from a variety of sources, from biomass-burning cookstoves and forest fires to natural gas pipeline leaks.
This new study used computer models to estimate how the oceans would respond to global warming, and also used estimates of future emissions of heat-trapping gases. The study acknowledges the wide range of projections of future sea-level rise, owing in part to a lack of understanding of how the massive land-based ice sheets such as Greenland and Antarctica will respond to global warming.
Instead of trying to arrive at a particular projection of sea level rise, as other researchers have done, the study focused on how pollution reductions would change the course of sea level rise.
Benjamin Horton, a professor at the University of Pennsylvania who studies sea level rise and was not involved in the study, said this approach was “simple,” and yet provides for a convincing case that tackling short-lived pollutants is important for slowing climate change in the next few decades. “They tackled the problem of sea level [rise] very simply and I think appropriately for this question,” he said in an interview.
Veerabhadran Ramanathan, the lead author of the study and a scientist at the Scripps Institution of Oceanography, told Climate Central that there is a need to address both short-lived pollutants and CO2 in order to avoid the worst near and long-term impacts from global warming.
“We cannot do it with CO2 alone,” he said. “By not taking actions about two decades ago, we have lost the luxury of doing one thing at a time. We have to reduce both CO2 and short-lived climate pollutants.”
In addition to slowing sea level rise, research has shown that reducing short-lived climate pollutants such as black carbon (which is largely generated from wood and dung-burning cook stoves in developing countries) would also have major public health benefits, saving up to 4.7 million lives worldwide per year.
Soot emissions can be reduced through the use of cleaner-burning cookstoves that don’t rely on burning biomass for fuel, as well as cutting the use of dirty forms of diesel fuel. Methane emissions can be reduced by controlling leaks from natural gas pipelines, and using different agricultural practices.
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