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April 03, 2007

Is It Getting Hot In Here?
Are Humans Causing Global Warming?

Submitted by Dirk Avery

The two most salient issues related to global warming are whether humans are causing it and what will happen to humans if the Earth continues to warm.

Answering the question of whether humans are causing global warming will inform the answer to the question of whether humans can or will do anything about it. Even if humans have caused it, can they do anything to reverse it? If we did not cause it, might we nevertheless reverse it?

There are some facts that are not in dispute. The Earth has warmed about one degree over the last century. “Greenhouse” gases in the atmosphere emit and re-direct long wave radiation emitted by the Earth back toward the Earth. The radiation warms the atmosphere. Carbon dioxide is a greenhouse gas; the most common atmospheric gases, nitrogen and oxygen, are not. Water vapor, a greenhouse gas, causes the greatest portion of the greenhouse effect. Methane and ozone are other greenhouse gases. Without the greenhouse effect, the Earth would be on average 70-90 ºF colder and far less habitable. The oceans, biosphere, and volcanoes are major sources of naturally occurring CO2.

Some facts related to sea levels are also not in dispute. Measuring sea levels involves complex calculations. Scientists differ in their estimates of both how sea levels have changed over the last century and at what rate levels are currently changing. Some scientists estimate levels have not increased over the last century, while many others believe levels have risen between 4 and 8 inches during the same time. Over the last 500 million years, sea levels have varied by over 1300 feet. Present sea levels are significantly lower than long-term averages over millions of years.

Many scientists who are alarmed by global warming believe that increasing CO2 is a cause of atmospheric imbalance. They believe that as the Earth warms, more water will evaporate from the surface exacerbating the warming. A subset of those concerned by global warming believes that human activities are the primary cause of increasing CO2 and other greenhouse gases. Most scientists readily admit that the study of the climate is complex and uncertain even when they believe that anthropogenic CO2 is likely driving the observed warming.

Some prominent scientists, including Sir David King, of the University of Cambridge Surface Science Group, believe that if human production of CO2 and global warming continue at their current pace, the Earth will become largely uninhabitable by the end of this century. In this scenario, all ice on the planet will melt, sea levels will rise, and Antarctica may be the only habitable continent. Other prominent scientists have less severe predictions but still foresee increasingly inclement weather, increased precipitation, and rising sea levels.

Under much of Antarctica’s nearly 1.6 km thick ice, there is soil. Cataclysmic ice melting in Antarctica could, therefore, result in rising sea levels. The Artic, on the other hand, is largely floating sea ice. If all the sea ice melted, it would raise sea levels as much as a melting ice cube raises the water level in a glass – not at all. The melted ice would, however, influence the ocean circulation and freshen the seawater of the North Atlantic affecting its biosphere. Many scientists agree that shore ice in Antarctica is melting, while most also agree the continent is cooling. Some scientists believe the melting sea ice will open the way for land-based glaciers to flow into the sea, causing a rise in sea levels. Skeptical scientists question global warming theories based on the seeming contradiction of cooling temperatures and melting ice. They explain the melting rather as a result of ice “memory,” or reactions to past conditions which play out over decades or centuries.

Some skeptical scientists also argue that sea levels have been increasing at a steady rate for thousands of years. During that time the Earth has experienced warmer and cooler periods than now, demonstrating, they argue, that temperature and sea levels are not closely correlated over relatively short periods of time.

Ice core studies like those described in Al Gore’s An Inconvenient Truth have shown a correlation between CO2 and the Earth’s temperature. Some scientists, such as Ian Clark of the Department of Earth Sciences at the University of Ottawa, agree that there is a correlation but suggest that in the past, increased CO2 is the effect of the Earth warming, not its cause. Instead, scientists such as Clark argue that the primary cause of warming is solar radiation. They substantiate this theory by showing a close correlation between solar activity and atmospheric temperatures. They interpret ice core studies to show that after periods of warming, caused by solar activity, CO2 levels increased in correlation hundreds of years later. Due to their size, oceans take hundreds of years to warm or cool. As oceans warm, they release vast amounts of CO2 and water vapor. Thus, a correlation exists, they claim, but the causation is reversed from that proposed by Al Gore.

Many people concerned with global warming point to consensus within the scientific community regarding global-warming science. The Intergovernmental Panel on Climate Change (IPCC) report confirming global warming theories was reviewed by 2,500 scientific experts. Skeptical scientists argue that this number is not limited to scientists with expertise in the area, and that it includes scientists who disagree with its conclusions and many non-scientist political figures and less prominent reviewers. When Professor Paul Reiter, of the Pasteur Institute of Paris, resigned from the IPCC in protest of the report, the IPCC initially refused to remove his name from the report. Only by threatening legal action did he get his name removed. Frederick Seitz, former president of the National Academy of Sciences, claimed that scientists’ views were censored in the IPCC report. Statements such as, “None of the studies cited has shown clear evidence that we can attribute climate changes to increases in Greenhouse Gases,” were removed.

Indeed, skeptics argue that much of current climate study is based on alarm. Funding for groups predicting the status quo quickly dries up, and dissenting scientists are bullied into agreement with those foretelling disaster. Dissenting scientist Timothy Ball has received death threats for his dissenting views, while others, including Richard Lindzen and Henk Tennekes, have been fired or publicly smeared.

If humans are causing global warming through CO2, both sides agree that major changes are needed. Scientists estimate that an 80% reduction in human-produced CO2 would be necessary to make a difference. Such a radical reduction, in the absence of new technologies, would drastically change the way people in industrialized countries live. Collective-action problems are likely to inhibit the effectiveness of CO2 reduction without strong national and likely international government intervention. Despite the fervor of CO2 reduction advocates, the question remains whether people are willing to live with such an imposition.

This article was reviewed by Natalia Andronova, Ph.D. Atmospheric Science & Geophysics, a research scientist at the University of Michigan Department of Atmospheric, Oceanic and Space Sciences.