海角大神

Research from retired NASA Goddard Space Flight Center scientist H. Jay Zwally made headlines this week for finding that 鈥� contrary to popular belief 鈥� Antarctica is gaining more ice than it鈥檚 losing ... for now.

But Dr. Zwally warned in a NASA announcement that, 鈥淚t could take only a few decades for the .鈥�

Zwally didn鈥檛 dispute that sea levels are rising, telling 海角大神 in an interview, it鈥檚 鈥渄efinitive, there鈥檚 no question about that." But they鈥檙e not rising because of ice melt on Antarctica, he says.

In last week鈥檚 paper, Zwally, who is now affiliated with the Earth System Science Interdisciplinary Center at the University of Maryland in College Park, said his satellite and meteorological data analysis showed that overall Antarctic land ice has gained mass. 聽

Much of Zwally鈥檚 latest analysis is based on data collected using a laser tool on a NASA satellite called the Ice, Cloud, and land Elevation Satellite ().

ICESat聽travels in the polar orbit with a laser shooting out pulses of light to measure how long it takes it to hit the Earth鈥檚 surface and bounce back. Over time, depending on how long it takes the light to travel to and from the same locations on Earth, ICESAt can tell how the elevation on land is changing.

But Zwally鈥檚 findings about land ice on the southern continent contradict previous research that has showed that Antarctica has lost ice overall, based on data collected from a NASA mission called Gravity Recovery and Climate Experiment () of a pair of satellites that measure the tiny variations in the Earth鈥檚 gravity field to determine the amount and density of the mass below.

Some scientists, like Ted Scambos, senior researcher at the National Snow and Ice Data Center in Boulder, Colo., say that ICESat data is inaccurate.

鈥淭here鈥檚 no real way to reconcile this paper with the finding of half a dozen labs using the GRACE satellite, which consistently indicate that Antarctica is losing mass overall,鈥� he points out in an e-mail to the Monitor.

Dr. Scambos points to studies that have found problems with ICESat, but says he .

More ice or less ice, here are a few important takeaways from the discussion:

1. Measuring land ice in Antarctica is hard

Scientists agree that none of the data-gathering tools are perfect. What they don鈥檛 agree on is which measurement tool 鈥� GRACE or ICESat 鈥� provides the most accurate data.

鈥淵ou鈥檙e talking about a continental-size area and changes in centimeters and millimeters,鈥� explains Thomas P. Wagner, a NASA climate scientist, in an interview with the Monitor.

鈥淚t鈥檚 very, very difficult to do this from space with a satellite, but one of the only ways to do it is by satellite,鈥� he explains.

But scientists are constantly improving their tools and learning more about the ice sheets. NASA is launching a second-generation ICESat in 2018, with more and better lasers and detectors that will circle the globe and, for the first time, report real-time, continuous data collected over larger swaths of land. NASA also plans to upgrade GRACE. 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽聽

2. Sea levels are rising聽 聽聽

Sea levels are rising at (3.2 millimeters per year) of the 20th century, UN's Intergovernmental Panel on Climate Change (IPCC) says. And it鈥檚 鈥渧irtually certain鈥� that this trend will continue for many centuries.

Up until this century, ice melt on land has made only a small impact on sea level rise. About two-thirds of it has come from thermal expansion, or ocean that鈥檚 heating up from a warmer climate and causing the water to expand, according to Julien P. Nicolas, an atmospheric scientist at Ohio State University.

But, 鈥減olar ice sheet and melting glaciers鈥� contribution is rapidly growing and we expect that in the 21st century might become most important source of sea level rise,鈥� Dr. Nicolas, who was also a contributing author on sea level rise in the 2013 report from the IPCC, told the Monitor in an interview.

3. The globe is still warming

The IPCC, an organization of scientists from around the globe, says and that it is at least 95 percent certain that humans are the main cause. And if temperatures continue to rise unabated, says the group, it is 鈥渧ery likely鈥� we鈥檒l see increase in intensity and quantity of heat waves and extreme precipitation. The ocean, says the IPCC, will continue to warm and acidify, and sea level will continue to rise.