The global sea level this summer is a quarter of an inch lower than last summer, according to NASA scientists, in sharp contrast to the gradual rise the ocean has experienced in recent years.
The change stems from two strong weather cycles over the Pacific Ocean — El Niño and La Niña — which shifted precipitation patterns, according to scientists at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. The two cycles brought heavy rains to Brazil and Amazon, along with drought to the southern United States.
Researchers monitored the ocean’s width, height, temperature and salinity through satellites and robot-operated floats, and presented their findings Aug. 8 and 9 at the annual Gravity Recovery and Climate Experiment (GRACE) Science Team Meeting in Austin, Tex.
“This year the continents got an extra dose of rain, so much so that global sea levels actually fell over most of the last year,” said Carmen Boening, an oceanographer and climate scientist at the lab, in a statement.
Climate scientist Josh Willis, who also works at NASA’s Jet Propulsion Laboratory, warned that this water will eventually return to the ocean, and the long-term trend of rising sea levels will continue.
“What this show is the impact La Niña and El Niño can have on global rainfall,” he said in an interview, adding scientists need to get a better sense of ice sheet dynamics before they can offer a more precise estimate of future sea level rise. “We really have a lot left to understand before we can do better.”
According to computer climate models, sea levels are expected to rise because water expands as it warms, and the melting of glaciers and ice sheets in Greenland and Antarctica will contribute to global sea levels. The U.N. Intergovernmental Panel on Climate Change gave what it called a conservative estimate in 2007 that the ocean could rise between 7 and 23 inches by 2100. Recent research suggests it could rise by as much as 2.5 to 6.5 feet during this period.
The question of how much the ocean could rise due to warming is a topic of intense debate. In the past two decades global sea levels increased at a rate of roughly 0.12 inches a year, compared to 0.07 inches from 1961 to 2003, according to satellite data. A recent tide gauge study of sea levels in Australia and New Zealand, published in the Journal of Coastal Research, provided readings that suggested the rate of ocean rise has declined in the past decade.
Patrick J. Michaels, a senior fellow at the libertarian Cato Institute, noted that recent satellite data shows a slight decline in the rate of sea-level rise, which casts doubt on whether the ocean will expand as some predict by the end of the century.
“I suspect it would have to start rising pretty rapidly in order to fulfill those projections,” Michaels said in an interview.
The findings came as the Government Accountability Office released a report Thursday examining proposed technological methods aimed at manipulating the climate, known as ”geoengineering.”
The GAO report, commissioned by former House Science Committee chairman Bart Gordon (D-Tenn.), concluded that “climate engineering technologies are not now an option for addressing global climate change” given their cost, potential effectiveness and possible consequences. But the report said that the majority of experts the GAO surveyed “supported starting significant climate engineering now” in case humans faced drastic climate change in future decades.
The report identified capturing carbon dioxide from the air and then storing it as the most promising climate engineering technique right now.
Carnegie Institution scientist Ken Caldeira, an expert on climate engineering, wrote in an e-mail that he welcomed the fact that the GAO made a distinction between carbon-capture technologies and ones aimed at deflecting solar radiation. But he questioned why the analysts focused on the need for coordinating geoengineering research, rather than a broader response to the problems climate change poses.
“We need broad coordination of activities to reduce climate risk,” Caldeira wrote. “I don’t think we need coordination only among the narrower, yet very heterogeneous set of activities commonly labeled as ‘geoengineering.’ ”