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Paul Wellman

New Study Predicts
Greater Sea-Level Rise

Higher Tide


Record summer heat waves, melting glaciers, and droughts offer compelling evidence that rapid climate change is happening, and media attention on the subject of global warming has been extensive for the past couple of years, from Al Gore’s Oscar-winning documentary An Inconvenient Truth to the report published by the UN Intergovernmental Panel on Climate Change (IPCC) this spring. However, a group of six American scientists-including UCSB paleoclimatology professor David Lea(pictured above, left, with NASA’s James Hansen) -recently published a paper stating that the IPCC’s sea-level rise estimate of approximately 16 inches during the next century is too conservative.

The group-led by James Hansen, of the NASA Goddard Institute for Space Studies-predicts a sea rise of about 20 feet by 2100. The paper-which references nearly 100 scientific articles, publications, and statistical reports-unequivocally states that “recent greenhouse gas emissions place Earth perilously close to dramatic climate change that could run out of control, with great dangers for humans and other creatures.”

The 29-page paper was published in the July 15 issue of Philosophical Transactions of the Royal Society of London, Series A-the oldest English-language scientific publication in existence. This is the second paper Lea and Hansen have collaborated on together. The first paper focused more on global temperature change, while this one scrutinizes sea-level rise specifically-a pertinent issue in coastal communities like Santa Barbara.

Lea’s specialty being paleoclimatology, he used his knowledge of climatic conditions from the past to formulate a model for present and future conditions. He said that the team’s purpose is to incorporate his paleoclimatic data with recent climate data to create more accurate projections about global temperature rise. Lea maintains that the key point in this issue is how sensitive the Earth’s climate is to carbon dioxide (CO ) levels. “That sensitivity will determine how this will play out over the next century. We know how much CO we’re pumping out; the unknown is how the climate will shift to compensate,” he commented.

CO is particularly important in the issue of global warming, as it is the most abundant human-produced greenhouse gas (GHG). Other GHGs include methane (CH ), ozone (O ), nitrous oxide (N O), and black carbon, or “black soot.” GHGs, while allowing heat from the sun to enter Earth’s atmosphere, effectively block heat that would ordinarily be reflected out into space. The result is an increase in atmospheric temperature, causing ice sheets to melt and expose darker patches of earth, which absorb heat and increase ground temperature. According to the study Lea worked on, this process-called “positive feedback”-accelerates the melting of ice and the rise in global temperatures. The paper in the Royal Society states, “Only intense simultaneous efforts to slow CO emissions and reduce non-CO forcings can keep climate within or near the range of the past million years.”

The group obtained the same temperature rise estimate-three degrees Celsius-for the next century found by the IPCC, but concluded that the IPCC’s sea-rise projection was inconsistent with paleoclimatic data and observations of the current rate of ice sheet melt. According to Lea, paleoclimatic records point to a more dramatic increase of global temperatures at the poles, leading to accelerated melting of the ice sheets. This is why his group’s sea-level rise estimate is so much higher than that of the IPCC.

Susan Solomon of the U.S. National Oceanic and Atmospheric Administration was the co-chair of the IPCC’s Working Group I. She said she viewed this new estimate not as a refutation of the IPCC’s, but as a broadening of the information available on the topic of global warming. “There are a lot of views on this topic,” she said. “This is an incredibly complex subject, and I think it’s great that people continue to work on it. The jury’s still out on it-we don’t have all the answers yet.” Tapio Schneider, a professor of environmental science and engineering at Caltech, said he viewed the study somewhat more critically. “The conclusions of Hansen, et al., that the West Antarctic and/or Greenland ice sheets may disintegrate more rapidly than commonly thought are highly speculative,” he said. Schneider added, however, that current levels of GHG emissions would make it unlikely for the ice sheets to exist at their present size.

Lea first became interested in the subject of global warming 20 years ago, while pursuing his PhD at the Massachusetts Institute of Technology. At that time, the first records from ice cores at Antarctica’s Vostok Station were published, indicating that CO levels in the atmosphere are directly related to global temperature. Scientists took samples of the air bubbles trapped deep in the ice to determine CO levels in the atmosphere. The depth of the ice correlates to the time period being studied.

Lea took this principle to tropical climes, where he examined the shells of sea surface microorganisms embedded in deep-sea sediments to create a record of past CO and temperature levels. By examining the shells, he found that temperatures in equatorial regions don’t fluctuate as widely as those at the poles. His research also showed that the Western Pacific and Indian oceans have a major impact on global temperatures. He states, “[The Western Pacific] is a major source of heat for the world’s oceans and for the global atmosphere.” Furthermore, his research indicates that the Western Equatorial Pacific and Indian oceans are as warm as or warmer than they have been at any time during the past 12,000 years. It was this research that first caught the attention of James Hansen and his group.

As a resident of Santa Barbara for the past 18 years, Lea feels that this area will certainly be affected by global climate change. “The general prediction is that the Southwest will experience a drying out, but Santa Barbara is tough to predict, since it’s in a coastal area,” he said. “I think water will be a huge issue, as precipitation will decrease.”

Lea said he feels that Santa Barbara is headed in the right direction, particularly in light of public outreach and progressive environmental policies in place here. “[Climate change] is a difficult problem to solve, especially when we get 85 percent of our energy from fossil fuel,” he said. “Mayor Blum is very progressive,” he added, pointing out the city’s use of more hybrid vehicles in its fleet and improvement of the bicycle infrastructure. “Santa Barbara has always been progressive on environmental issues.”

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