Impacts Observed & Projected – Page 115

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16 November 2015, Science Daily, Earth’s climate more sensitive to carbon dioxide than previously thought. Ancient climates on Earth may have been more sensitive to carbon dioxide than was previously thought, according to new research from Binghamton University. A team of Binghamton University researchers including geology PhD student Elliot A. Jagniecki and professors Tim Lowenstein, David Jenkins and Robert Demicco examined nahcolite crystals found in Colorado’s Green River Formation, formed 50 million years old during a hothouse climate. They found that CO₂ levels during this time may have been as low as 680 parts per million (ppm), nearly half the 1,125 ppm predicted by previous experiments. The new data suggests that past predictions significantly underestimate the impact of greenhouse warming and that Earth’s climate may be more sensitive to increased carbon dioxide than was once thought, said Lowenstein. “The significance of this is that CO₂ 50 million years ago may not have been as high as we once thought it was, but the climate back then was significantly warmer than it is today,” said Lowenstein. CO₂ levels in the atmosphere today have reached 400 ppm. According to current projections, doubling the CO₂ will result in a rise in the global average temperature of 3 degrees Centigrade. This new research suggests that the effects of CO₂ on global warming may be underestimated. “Take notice that carbon dioxide 50 million years ago may not have been as high as we once thought it was. We may reach that level in the next century, and so the climate change from that increase could be pretty severe, pretty dramatic. CO₂ and other climate forcings may be more important for global warming than we realized.” The only direct measurement of carbon dioxide is from ice cores, which only go back less than 1 million years. Lowenstein and his team are trying to develop ways to estimate ancient carbon dioxide in the atmosphere using indirect proxies. He said that their approach is different than any ever undertaken. “These are direct chemical measurements that are based on equilibrium thermodynamics,” he said. “These are direct laboratory experiments, so I think they’re really reliable. Read More here

14 November 2015, Climate News Network, Greenland glaciers’ melting speeds up again. The increasing rate at which Greenland’s glaciers are melting this century has confounded polar scientists. A massive Greenland glacier that holds enough water to raise sea levels by half a metre is melting at speed, according to a new study. The Zachariae Isstrom in northeast Greenland has entered a phase of accelerated retreat, and is losing mass at the rate of 5 billion metric tons a year, according to US scientists. They report in the journal Science that a succession of aerial surveys combined with multiple satellite observations has established that the base of the glacier is being eroded rapidly by a mix of warmer ocean water and increasing amounts of meltwater from the surface of the Greenland ice sheet. “North Greenland glaciers are changing rapidly,” said Jeremie Mouginot, an earth system scientist at the University of California, Irvine, who led the study. “The shape and dynamics of the Zachariae Isstrom have changed dramatically over the last few years. The glacier is now breaking up and calving high volumes of icebergs into the ocean, which will result in rising sea levels for decades to come.” Read More here

13 November 2015, Climate News Network, Global warming drains the water of life. Melting snowpack in Turkey’s Lesser Caucasus mountains. New research warns that rising temperatures are reducing the mountain snow on which billions of people in lowland areas depend for their water supply. Up to two billion people who depend on winter snow to deliver their summer water could see shortages by 2060 as upland and mountain snowpacks continue to dwindle. An estimated 300 million people could find, 45 years on, that they simply won’t have enough water for all their needs, according to new research. Climate change driven by rising atmospheric levels of carbon dioxide – in turn, fed by human combustion of fossil fuels – may already be affecting global precipitation. Researchers have consistently found that much of the world’s drylands will increase as global average temperatures rise. But warmer temperatures increasingly also mean the water that once fell as snow, to be preserved until the summer, now falls as winter rain, and runs off directly. The snow that does fall is settling at ever higher altitudes and melting ever earlier. Reliable flow This is bad news for agricultural communities that depend on a reliable flow of meltwater every summer. California is already in the grip of a sustained drought, made worse by lower falls of snow. Great tracts of Asia depend on summer meltwater from the Himalayan massif and the Tibetan plateau. Justin Mankin, an environmental scientist at Columbia University’s Earth Institute in the US, and colleagues report in Environmental Research Letters journal that they studied 421 drainage basins across the northern hemisphere. Read More here

10 November 2015, Science Daily, Geophysics could slow Antarctic ice retreat. Gravitational effects, variations in Earth structure could damp rise in global sea levels. The anticipated melting of the massive West Antarctic Ice Sheet could be slowed by two big factors that are largely overlooked in current computer models, according to a new study. The findings, published online in Nature Communications, suggest that the impact on global sea levels from the retreating ice sheet could be less drastic — or at least more gradual — than recent computer simulations have indicated. Over the past year, numerous studies have warned that parts of the West Antarctic Ice Sheet are on the verge of a runaway retreat. Just last week a high-profile research paper forecast that this could lead eventually to a rise in global sea levels of as much as three metres. The authors of the new Nature Communications paper, however, focus on two geophysical elements that they say aren’t adequately reflected in computer simulations for this region: the surprisingly powerful gravitational pull of the immense ice sheet on surrounding water, and the unusually fluid nature of the mantle beneath the bedrock that the ice sits on. “The fate of the polar ice sheets in a warming world is a major concern for policy makers — and attention is rightly focused on the importance of restraining CO₂ emissions and preparing for rising sea levels,” says lead author Natalya Gomez, an assistant professor of Earth and Planetary Sciences at McGill University in Montreal. “But our study shows that for Antarctica, in particular, computer models also need to take into account how gravitational effects and variations in Earth structure could affect the pace of future ice-sheet loss.” Read More here

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