Climate change may threaten tens of millions more people than previously believed, according to a new study that says previous research used incorrect information about water levels along the world's coastlines.
The new research, published March 4 in the peer-reviewed British journal Nature, found that more than 90% of the existing sea-level studies use a reference sea level that is lower than the actual sea level along the coast. That means alreadydire projections about sea level risemight be underestimating the risk.
"Our calculations show that measured coastal sea levels in many places on Earth are higher than is often assumed in coastal impact studies," said study lead authorKatharina Seeger, of the University of Paduain Italy, in a statement. "Our findings make it necessary to re-evaluate and, in most cases, update the underlying methodology of all existing coastal hazard studies," she added.
What is sea-level rise?
Sea-level rise, one of the clearest signals of human-caused global warming, is driven by warming and expanding ocean water, as well as the melting of mountain glaciers, ice caps and the vast Greenland and Antarctic ice sheets.
Seas have risen nearly 8 inches worldwide since 1880, but unlike water in a bathtub, they don't rise evenly.
In the past 100 years, for example, water has climbed about a foot or more in some U.S. cities because of ocean currents and the natural settling of land.
Scientists said global warming will be the primary cause of sea-level rise. The greatest uncertainty is how quickly the massive West Antarctic ice sheet will melt.
What causes global warming?
Human-caused climate change is caused by the burning of fossil fuels such as gas, coal and oil, which release greenhouse gases such as carbon dioxide (CO2) and methane into the atmosphere. This extra CO2 causes temperatures of the atmosphere and oceans to rise to levels that cannot be explained by natural causes.
Why is sea-level rise important?
Rising seas increase the risk of coastal flooding, putting tens of millions of people in the United States and hundreds of millions worldwide at risk. Around 40% of the world's population lives within 62 miles of a coast. As climate change impacts our world, sea level rise has become a pressing issue for many coastal communities.
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Specifically, in the new study, the authors found that compared with previous estimates a hypothetical 1 meter of sea-level rise could put up to 37% more land below sea level, impacting 77–132 million people across the globe.
What does the new study show?
According to the new study, most previous sea-level studies do not reflect reality because they do not use direct measurements of sea level or combine sea level and land elevation data incorrectly.
Study co-authorPhilip Minderhoud, a hydrogeology professor at Wageningen University & Research in the Netherlands, said, "We seem to be dealing with an interdisciplinary blind spot between sea level science on one hand and continent-based coastal hazard impacts science on the other."
One simple way to understand this is that many studies assume sea levels without waves or currents, when the reality at the water's edge is of oceans constantly roiled by wind, tides, currents, changing temperatures and things like El Niño, Minderhoud and Seegertold the Associated Press.
"We hope that this approach can become a new standard for more accurate assessments of future coastal impacts," conclude the authors in the study.
What regions are most at risk?
These underestimations of sea-level rise were particularly noteworthy in the Global South — specifically in Southeast Asia and the Pacific region.
Underestimates were also observed in Latin America, the west coast of North America, the Caribbean, Africa, the Middle East and the Indo-Pacific.
What do others think of the study?
"I do think the new Nature sea level rise article is significant," saidMichael Mann, of the University of Pennsylvania, who was not part of the study. "It does look as if the entire community has overlooked the key distinction they draw and that this does mean we might be underestimating (by a substantial margin) the potential sea-level rise in many key regions.
"There is still quite a bit of uncertainty because of complications due to changing ocean currents, etc., but this study does seem significant to me," Mann told USA TODAY.
This article originally appeared on USA TODAY:A deadly climate change effect has been underestimated, study finds