Climate change is natural - Believe the science, not the rhetoric: We aren't causing global warming, say scientists

The Globe and Mail

Tuesday, November 19, 2002
Print Edition, Page A21

The Kyoto Protocol assumes humankind causes global warming, but climate has always changed. For two million years, the Earth has been in an ice age marked by more than 30 glaciations, during which ice sheets covered most of North America to a depth of several kilometres. In the past 800,000 years, the pattern has been 100,000 years of extensive glaciation, interspersed with brief, warmer interglacials of 15,000 years. The next glaciation is less than 5,000 years ahead.

Greenhouse gases, clouds and aerosols in the atmosphere do trap some of the solar radiation reflected from the Earth's surface, causing a natural greenhouse effect that warms the Earth and makes it habitable. Those gases comprise less than 0.1 per cent of the air. They include carbon dioxide, methane, nitrous oxide, and the most important one, water vapour. Water vapour, comprising 99 per cent of greenhouse gases in the atmosphere, provides most of the greenhouse effect, followed by water in all its phases in clouds.

During the past 300 years, atmospheric carbon dioxide concentrations have risen from 275 parts per million to around 360 parts per million, a 30-per-cent increase. Most of the increase has been recent, caused by fossil fuel burning and deforestation. Contrary to pro-Kyoto rhetoric, however, the increase in atmospheric carbon dioxide content, while clearly linked to postwar industrialization, is not a significant driver of global warming.

The proportion of carbon dioxide in the atmosphere has varied significantly over geologic time. The atmospheric concentration of carbon dioxide was more than 1,000 per cent higher than today's value during the Ordovician glaciation, around 440 million years ago.

Over the past 150,000 years, carbon dioxide levels have closely paralleled temperatures. However, detailed analysis indicates that CO2 levels often rose and peaked several hundred years after temperature did, meaning climate change drives major changes in CO2, not the reverse. Carbon dioxide is only a minor contributor in the many factors that influence global climate.

Climate has been warmer and colder in the past, before significant fossil fuel use. From about 900 to 1300 AD, the climate was warmer than it is today. A 500-year cooling followed, then a warming trend. By the 20th century, the global average surface temperature had risen about 0.6 degrees Celsius.

The 20th-century temperature record shows three trends: first, a warming trend of about 0.5 degrees Celsius that began in the late 19th century and peaked around 1940. Next, temperature decreased from 1940 until the late 1970s. Then a warming trend occurred. Because about 80 per cent of the carbon dioxide from human activities was added to the air after 1940, the early 20th-century warming and the mid-century cooling trends were largely natural, not CO2-driven.

Computer simulations of human-made global warming predict significant warming not only near the surface but also in the lower troposphere, from two to eight kilometres up. But this doesn't seem to be the case. Records from NASA's Microwave Sounder Units aboard satellites extend back 22 years and cover most of the globe. They are validated by other measures. The records show that the temperature of the lower troposphere does vary as a result of natural factors. The strong el Nino warming pulse of 1997-1998 is an obvious example. However, no meaningful human-caused warming trend, as forecast by the computer simulations, can be found.

When compared to the observed response of the climate system, the computer simulations all have forecast warming trends much steeper over the past several decades than was measured. The forecasts exaggerate somewhat the warming at the surface, and profoundly in the lower troposphere.

A middle-range forecast of future warming, based on expected growth in fossil fuel use without any curbs, as compiled by the United Nations Intergovernmental Panel on Climate Change, forecasts a 1 degree Celsius increase between now and 2050. Compliance with the Kyoto Protocol would reduce that increase by an insignificant 0.06 degrees.

Computer models that predict catastrophic human-induced global warming have consistently failed to accurately reproduce past and present climate changes, so their 100-year forecasts are suspect. These models speculate that the air's increased carbon dioxide concentration is a major driver of atmospheric warming, by way of amplification processes. Without these speculative processes, even a doubling of CO2 concentration would lead to a theoretical surface warming of only approximately 1 degree.

Most of the 20th-century surface warming is inconsistent with a human-made enhanced greenhouse effect. However, temperatures over the past 250 years do show a strong correlation to the energy output of the sun (see chart). The sun's shorter magnetic cycles are more intense, suggesting periods of a brighter sun, then a fainter sun during longer cycles. Data since 1986 is consistent with these trends.

Based on analysis of ancient and recent temperature and atmospheric data, increased atmospheric concentrations of carbon dioxide are not a cause of significant global warming, contrary to forecasts by computer simulations. The magnitude of human-caused warming is especially constrained by the observed temperature trends of the lower troposphere. There is strong evidence that variation in the sun's energy output is a much more significant driver of surface temperature than human-made greenhouse gases.

When it to comes to climate change, humans aren't the culprits.
Dr. Sallie Baliunas is deputy director at Mount Wilson Observatory and an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. Dr. Tim Patterson is a professor of geology (paleoclimatology) in the Department of Earth Sciences at Carleton University in Ottawa. Allan M. R. MacRae is a professional engineer, investment banker and environmentalist. Views expressed are not necessarily those of any institution with which the authors are affiliated.


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