Global sea level is projected to rise between 7 and 23 inches by 2100, according to the Intergovernmental Panel on Climate Change (IPCC). Recent melting of the Antarctic ice sheet has prompted geophysicists at the University of Toronto and Oregon State University to warn that global sea level could rise 25 percent beyond the IPCC projections. These catastrophic long-term predictions tend to overshadow the potentially devastating near-term impacts of global sea-level rise that have, in some places, already begun.
“Much of the world’s cropland—especially in the developing world—is close to sea level and near the shore,” writes Joseph Romm, a senior fellow at the Center for American Progress. As sea level rises, salt water seeps into tidal estuaries and groundwater aquifers, dramatically changing the salinity of the water, drying out land, disrupting agriculture, and limiting freshwater availability.
Salt water infiltration into coastal freshwater aquifers, known as “extended salt wedge,” threatens both marine life and terrestrial vegetation. In Bangladesh, extended salt wedge is already causing panic. “It’s already too salty for traditional crops,” farmers told Nature. “This area was all [rice] paddy before. Now, no paddy…The trees look nice, but the coconut trees—there are no coconuts on them.”
Bangladesh’s Sundarbans mangroves, one of the world’s great biodiversity hotspots, are “breeding grounds for fish and shrimp, and a refuge for the last few hundred remaining wild Bengal tigers.” But these mangroves need slightly salty water, so even a modest rise in sea level could harm them. Meanwhile, freshwater fish farms that sustain food stocks for local residents are threatened by salt water contamination that displaces or kills the fish. “If it gets more salty here, this population will not be able to live here. No paddy, no fish,” says Matthew Digbijoy Nath, a farmer near the southwestern coast. “How will people live?”
India is also already feeling the impact of sea-level rise. Mangroves have begun to appear 60 miles further from the delta than where they usually regenerate, suggesting that their usual spot has become too salty. This has severe implications for both inland and coastal residents who are protected by mangroves during severe storm surges. Climate experts have warned that climate change could produce more frequent and severe storms in India, and without mangrove regeneration along the delta, local communities could be devastated.
Meanwhile, salt water contamination in the Ganges, India’s largest river, is threatening freshwater ecosystems. Experts have “already spotted more saline water fish in the river,” says Pranabes Sanyal, the eastern India representative of the National Coastal Zone Management Authority. At the same time, changes in the Ganges’ salinity are “turning vast farmlands barren in the country’s east,” as adjoining groundwater aquifers become too saline and dry out the soil.
“There’s a certain level of climate change impacts that we can’t stop, so we need to start looking at adaptation measures,” says Doug Howell, regional executive director of the National Wildlife Foundation. In developing countries like Bangladesh, it is not the threat of being underwater that worries people—it is food insecurity and their ability to adapt. And in both the developed and developing worlds, adaptation will be key to sustainability and survival.
Figure: Trends in sea level rise from 1870 to 2006. According to coastal and island tide gauges, between 1870 and 2001, sea level rose 1.7mm annually. That rate of change significantly increased between 1993 and 2006 to an average of 3.1 ± .4mm annually. Courtesy of Hugo Ahlenius, UNEP/GRID-Arendal.