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The Rising Tide: Global Warming And World Sea Levels

The Rising Tide: Global Warming And World Sea Levels

by Lynne Edgerton

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The Rising Tide is the first analysis of global warming and world sea level rise. It outlines state, national, and international actions to respond to the effects of global warming on coastal communities and ecosystems.


The Rising Tide is the first analysis of global warming and world sea level rise. It outlines state, national, and international actions to respond to the effects of global warming on coastal communities and ecosystems.

Editorial Reviews

Library Journal
The warming of the global atmosphere caused by the greenhouse effect has resulted in a rise in the sea level, changed ocean circulation patterns, and more frequent and intense coastal storms. Scientific studies predict a further 0.7 meter rise by the year 2050, with significant effects on coastal areas: beaches and barrier island will be eroded and inundated; estuaries will become more salty; there will be saltwater intrusion into groundwater supplies; and commercially important fisheries will be affected. The author, an attorney with the Natural Resources Defense Council, outlines current methods for dealing with this problem and urges the implementation of retreat and relocation plans, the only strategies endorsed by planners and scientists. This volume, which includes appendixes of relevant state, federal, and international documents, is suitable for concerned general readers as well as elected officials and planners, and should be available in academic and public libraries in both inland and coastal regions. --Judith B. Barnett, Pell Marine Science Lib., Univ. of Rhode Island, Narragansett
Edgerton analyzes the world sea level rise related to global warming, and outlines state, national, and international actions to respond and adapt to the effects of global warming on coastal communities and ecosystems. Annotation c. Book News, Inc., Portland, OR (booknews.com)

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The Rising Tide

Global Warming and World Sea Levels

By Lynne T. Edgerton


Copyright © 1991 Natural Resources Defense Council
All rights reserved.
ISBN: 978-1-61091-471-0



In recent years, activities such as burning fossil fuels, leveling forests, and producing synthetic chemicals such as chlorofluorocarbons (CFCs) have unleashed into the atmosphere large quantities of carbon dioxide (CO2 and other "greenhouse" gases. These gases are warming the earth at an unprecedented rate. If current trends continue, they are expected to raise the earth's average surface temperature by at least 1.5° to 4.5° C, or more, in the next century—with warming at the poles perhaps two to three times as large as warming at the middle latitudes.

Is It Certain to Occur?

While large uncertainties remain about the timing and ultimate magnitude of climate change, recent research supports the fundamental understanding of the greenhouse effect that has emerged over the last decade. There is little dispute that there has been a significant increase in the global concentrations of heat-trapping gases during the last century. And the overwhelming conclusion from the body of published scientific literature is that this greenhouse gas buildup poses enormous risks.

An unusual aspect of the issue, however, is that the atmospheric warming observed over the past decade does not yet exceed historical natural climate variations, although the five global-average warmest years in the past century occurred in the 1980s. Thus policymakers are faced with considerable uncertainties. There is worry that current estimates of future warming may be too high, that the uncertainties in climate computer models may make action premature, that climate-stabilizing (negative) feedbacks have been omitted from current models.

Even assuming the legitimacy of these concerns, however, the mainstream scientific view of the greenhouse effect is not based solely on models. It is supported by observations of other planets, seasonal variations in the earth's climate, and, perhaps most important, on long- term changes in the earth's climate over the last 160,000 years. This evidence, in addition to model results, has been reviewed by numerous national and international scientific bodies—including the National Academy of Sciences, the Scientific Committee on Problems of the Environment, NASA's Goddard Institute for Space Studies, NOAA's Geophysical Fluid Dynamics Laboratory, and various laboratories of the Department of Energy (DOE). In an August 1990 report, the Intergovernmental Panel on Climate Change established by the United Nations Environment Program and the World Meteorological Organization summarized the scientific facts of which it is certain, as follows:

• There is a natural greenhouse effect that already keeps the earth warmer than it would otherwise be.

• Emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases: carbon dioxide, methane, chlorofluorocarbons, and nitrous oxide. These increases will enhance the greenhouse effect, resulting on average in an additional warming of the earth's surface. The main greenhouse gas, water vapor, will increase in response to global warming and further enhance it.

With regard to temperature observations, there are two key points. First, numerous reviews have reaffirmed that after correcting for urban heat islands and other potential systematic errors, there has been a statistically significant global warming of about 0.5° C over the last century. The U.S. temperature record shows less warming than the global average, but its statistical significance is marginal. This finding should come as no surprise, for the United States represents only 1.5 percent of the area of the earth and there is no inconsistency between a global warming and small regions of the earth showing insignificant warming or even cooling. Second, substantial variability and lags in global temperatures are expected. Because the oceans have a large heat capacity and because natural variability and other climate forcings (such as aerosol loadings) are similar in magnitude to the greenhouse gas buildup so far, the uneven pattern of global warming observed to date is not at all inconsistent with the climate models.

With regard to feedbacks, these uncertainties are recognized by everyone, but they cut both ways. That is, current predictions are at least as likely to be too low as too high. Indeed, as recently as 1988, scientific predictions were significantly underestimating the magnitude of the ozone hole. Biological and geochemical feedbacks that are not included in the current models are likely to amplify the warming substantially—by perhaps a factor of 2 or more. The hypothesis that warming will be substantially mitigated by increased convection that dries the atmosphere has never been published in the scientific literature; in fact, it has been widely rejected by the scientific community.

The risks associated with global warming are clearly enormous. While there will always be respectable scientists who question global warming predictions, they represent a minority within the scientific community. Although this does not prove that they are wrong, we should not be willing to bet the planet that the National Academy of Sciences, NASA, the Intergovernmental Panel on Climate Change, and other authoritative scientific bodies are wrong and the minority view is right.

There can be no excuse for not pursuing all policy options to reduce greenhouse gases that make economic and environmental sense in their own right. So far the United States is not doing that. Current policies will lead to substantial further accumulation of greenhouse gases. U.S. emissions increased by about 7 percent between 1988 and 1990, and the U.S. share of global emissions, after falling continuously for more than a decade, is now increasing. This is neither necessary nor desirable. This country's carbon dioxide emissions could be reduced 20 percent by the year 2000, increasing our economic competitiveness, reducing our dependence on imported oil, and lowering our contribution to global warming.

How Is Climate Change Measured?

When evaluating the current status of our climate, scientists compare the historical climate record with current observations and with the predictions of climate models. Since a certain amount of statistical variability in world climate is known to exist, they attempt to separate this natural variability, or "noise," from the true signals that represent real changes in the system balance rather than random fluctuations. Such work is carried out by developing "signal-to-noise ratios." The larger the apparent signal compared to the noise, the more certain scientists can be that the global climate is changing.

The key to understanding climate fluctuations often lies in our analysis of these shifts in both the human and proxy records (fossil records). Human records have been useful in elucidating short-term trends, although they are generally considered less reliable if collected before the year 1900. Proxy records are likewise inaccurate, and often incomplete, offering only limited resolution on the scale of hundreds to thousands of years.

On the other hand, ancient natural records provide us with a broad view of our climate's variability over time and indicate the effects of perturbations to the global climate system. By a variety of methods—including the analysis of gases trapped in air pockets of ancient ice flows and the analysis of oxygen and carbon isotopes from deep-sea sediment cores—scientists have been able to construct a historical record of atmospheric composition and global climates. They have found that global temperatures have varied widely throughout time and that sea levels have varied concurrently. Past climate changes, they hypothesize, have historically ensued from the combination of (1) periodic variations in the earth's orbit and changes in solar output that influence the distribution and amount of energy the earth receives from the sun, (2) catastrophic events such as meteorite impacts, volcanic eruptions, or changes in oceanic circulation, and (3) ongoing biological processes. Recent measurements indicate that humans have the ability to alter climate significantly as well.

By comparing historical data obtained from air bubbles trapped in ancient ice with current observations, changes above normal fluctuations in the ratios of certain atmospheric gases have been documented. Among these gases are carbon dioxide, methane, and nitrous oxide, which until the last few centuries had existed in a stable natural balance for millennia due to biological and chemical processes. Over geological time, these major gases have played a vital part in regulating the earth's climate.

The Greenhouse Effect

Water vapor, carbon dioxide, methane, nitrous oxide, and ozone comprise the natural fraction of what are called the greenhouse gases. These gases delay the escape of infrared radiation from the earth into space, thus causing a general climatic warming known as the greenhouse effect (by analogy to the warming that occurs in a greenhouse). Scientists have stressed that this is a natural process—indeed, the earth would be 33° C (63° F) cooler than it is presently if the greenhouse effect did not exist.

Human activities are now rapidly intensifying this natural greenhouse effect. Carbon dioxide concentrations have increased 25 percent since preindustrial times, methane concentrations have doubled, and chlorofluorocarbons have been introduced into the atmosphere for the first time. Human activities have not only directly added these greenhouse gases to the atmosphere, but they have greatly altered the chemistry of the global atmosphere by increasing the production of tropospheric ozone and decreasing the natural destruction of methane, thus further enhancing the greenhouse effect. The rate at which the greenhouse effect is intensifying—the rate of climate "forcing"—is now more than five times what it was during the last century.

During the 1980s carbon dioxide accounted for approximately 55 percent of the climate forcing, while CFCs accounted for about 24 percent. Methane and nitrous oxide together contributed approximately 21 percent. We turn now to the empirical evidence and its implications.


The increase in atmospheric carbon dioxide is due primarily to fossil fuel combustion (coal, oil, and gas) and deforestation. The most precise measurements of atmospheric CO2 were begun at Mauna Loa, Hawaii, in 1958. (See Figure 1.1.) The rate of observed CO2 increase since that time has closely followed fossil fuel consumption rates; consequently, the strong implication is that this source dominates any natural source and overwhelms any natural processes of removal.

Global deforestation is believed to be another important contributor to the increasing concentration of carbon dioxide. As land is cleared or burned for agriculture, or harvested for timber, CO2 is released into the atmosphere from the decay and oxidation of the carbon that had been incorporated in the trees and soil organic matter. These processes are estimated to contribute 10 to 30 percent of anthropogenic CO2 emissions. Although the future contribution of deforestation or reforestation to atmospheric CO2 levels could be significant, these aspects of the global carbon budget are little understood and have thus far been inadequately modeled. Control of future CO2 concentrations would benefit substantially from strengthened research in this area.

If nothing else in the earth's climatic system changed, a doubling of CO2 would raise the global average temperature 1.2° C. The earth's climatic system, however, is highly complex: A warming from increasing CO2, for example, causes corresponding changes in other parts of the system, such as increasing atmospheric water vapor and altering precipitation and cloud cover. Since the impact of these feedback mechanisms cannot be precisely determined, total warming is difficult to estimate. Sophisticated "general circulation models" (GCMs) of the earth's climate suggest that some of these feedbacks could be quite strong and would raise the warming by several degrees above that calculated by considering the CO2 increase alone. This finding is supported by the empirical evidence from historical changes in CO2 concentrations and climate revealed by the ice core measurements noted earlier.


Chlorofluorocarbons are produced exclusively in industrial activities. Because they remain in the atmosphere for approximately 100 years before breaking down, CFCs contribute substantially to global warming. Although CFCs comprise a relatively small proportion of the greenhouse gases by volume, they also destroy stratospheric ozone and produce 10,000 to 20,000 times more forcing per molecule in the atmosphere than CO2. CFCs are produced for such diverse uses as refrigeration and air conditioning, semiconductor manufacturing, degreasing solvents, and foam insulation.

Apart from their warming effects, CFCs have been identified as a major cause of the destruction of stratospheric ozone. As the stratospheric ozone layer thins, human beings become more vulnerable to the adverse health impacts of increased ultraviolet radiation. These impacts include skin cancer, cataracts and other vision disorders, broad systemic disruption of human immune responses, and possibly many other illnesses.

In September 1987, thirty-one nations met in Montreal and reached an international agreement to require a 50 percent reduction in the consumption of five CFCs by the end of this century. The EPA, however, estimates that an immediate 85 percent reduction of CFC emissions would be necessary merely to stabilize the amount of ozone-depleting substances reaching the upper atmosphere. In May 1988, just one day after the U.S. Senate's 83–0 ratification of the Montreal accord, the National Aeronautics and Space Administration (NASA) issued a report demonstrating that stratospheric ozone depletion is dramatically worse than was thought as recently as late 1987. The NASA report documents an unexpectedly rapid thinning of the stratospheric ozone shield all over the globe—with CFCs the likely cause. These alarming findings have added new urgency to NRDC's drive for a total phaseout of CFCs and other ozone-depleting chemicals.

According to the NASA report, even after natural factors are accounted for, satellite and ground-based monitors show ozone losses since 1969 as high as 3 percent over the heavily populated regions of North America and Europe and 5 percent over parts of the Southern Hemisphere. What is more, depletion is occurring at two to three times the rate predicted by the computer models scientists have relied on.


The growth of atmospheric methane and nitrous oxide has also caused global warming projections to rise. Methane, the major component of natural gas, is released to the atmosphere primarily from decomposition in wetlands, landfills, bogs, and rice paddies. It is also a by-product of digestion in cattle, sheep, and termites. Abiotic sources of methane include leaks from natural gas production and distribution, release of coal-seam gas during mining and processing, and incomplete combustion in slash-and-burn agriculture. Humans are responsible for the 11 percent increase in methane in the 1980s because they grow more rice, raise more cattle, produce more fuel, and clear more land (thus burning more material and possibly enhancing the habitat and food supply of termites). The cause of the continuing increase in the concentration of nitrous oxide is not clear at this time, but it could be due to the expanded use of nitrogen fertilizers around the world to improve agricultural productivity.

Another significant factor in global warming is ozone, which is created in the lower atmosphere (troposphere) by complex photochemical reactions involving nitrogen oxides, methane and other hydrocarbons, and carbon monoxide—the principal components of urban smog. Ozone is not uniformly distributed in the atmosphere like the other greenhouse gases, however, and its climatic impact depends strongly on its altitude. Thus while ground-level ozone is increasing, stratospheric (or upper atmospheric) ozone is decreasing. The overall impact on climate at the present time is unclear.

How Much Warming Is Inescapable?

Are we already experiencing the beginnings of the warming effects of increased concentrations of greenhouse gases? Expected global changes include warmer weather, warmer ocean water, a cooler stratosphere, increased precipitation, and a decrease in the daily range of temperatures.


Excerpted from The Rising Tide by Lynne T. Edgerton. Copyright © 1991 Natural Resources Defense Council. Excerpted by permission of ISLAND PRESS.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Meet the Author

Lynne Edgerton is a nationally and internationally recognized expert on global warming and sea level rise. As an attorney with the Natural Resources Defense Council in New York City for over six year, at the time of publication, she was involved in many environmental protection battles to preserve the nation's coasts, most notably as a litigator to secure the phase-out of the ocean dumping of New York City's contaminated sewage sludge offshore of New York and New Jersey. Ms. Edgerton holds degrees from both the undergraduate and law school of Vanderbilt University and from Yale School of Law. She served on the Board of the Climate Institute and is co-author of the coastal sections of the proposed International Convention on Climate Change submitted to the Intergovernmental Panel on Climate Change in February 1990. She was one of a small group of Americans invited by the United Nations Environment Program and the World Meteorological Organization to attend the 1990 Second World Climate Conference in Geneva, Switzerland.

In 1989, Ms. Edgerton co-founded NRDC's Los Angeles office. Since her arrival in Southern California, she has focused on securing clean air and clean coasts. She is co-author of No Safe Harbor, an NRDC report on oil tanker safety which recommends ways to lessen oil spill risks.

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