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Carbon dioxide
takes heat for
global warming

More than 99 percent of Earth's atmosphere is nitrogen and oxygen, while carbon dioxide constitutes just 370 molecules of air for every 200,000 molecules of oxygen. Yet it is an important substance that is taking the heat for causing global warming.

Although photosynthesis and respiration are often thought of as the balancing factors between carbon dioxide and oxygen in the atmosphere, the geological record says otherwise, and there are other factors such as deforestation, and wildfires that contribute to the balance.

Five hundred million years ago, carbon dioxide levels were nearly 20 times greater than today and Earth's temperature was about 20 degrees Fahrenheit higher.

Shortly after a rapid increase in carbon dioxide, following the "Cambrian Explosion" around 500 million years ago, there was a slow decline in atmospheric carbon dioxide, punctuated by a few peaks and valleys for 100 million years.

Then something happened and the levels began a sharp decline, reaching a minimum and leveling off near present day levels around 340 million years ago just after the beginning of the Carboniferous Period, a division of the geologic time named for the large amounts of coal that were deposited in stagnant swamps during the period.

The carbon dioxide level remained low for 60 million years throughout the Carboniferous and on into the Permian Period, which ended 245 million years ago.

Oxygen levels in the atmosphere varied only slightly from the time of the Cambrian explosion, but at about the same time that the carbon dioxide level began its sharp decline, the oxygen level began to rise sharply, reaching a peak just when the carbon dioxide level was at its lowest.

But at the beginning of the Carboniferous period, Earth was impacted by three large extraterrestrial objects that left craters, two of them 30 miles across, a third one twice that size. These all occurred within an 8-million-year period, a long time in human years, but the blink of an eye in geologic time.

The beginning of the Carboniferous period was also marked by a mass extinction that wiped out 75 percent of all species on Earth at the time, as is verified in the rock record worldwide, everywhere these fossils have been found, below the Carboniferous layers, but never within or above them.

Mass extinctions are not uncommon in the fossil record. Throughout Earth's history there have been quite a few of varying degrees of grievousness.

Many are associated in time with, and appear to have been caused by, impacts of extraterrestrial objects such as asteroids or comets.

The greatest extinction of all was the at the end of the Permian Period when 95 percent of all species went extinct. At the time of the Permian extinction the oxygen level had fallen back to a normal level of between 15 and 20 percent.

After the Permian extinction the carbon dioxide level rose again rapidly, reaching a peak of 2,500 parts per million in the middle of the Jurassic period 175 million years ago. Since then it has declined steadily with only a slight upward peak at the K-T mass extinction, which included the demise of the dinosaurs 65 million years ago.

The geological record shows that throughout most of Earth's history its temperature has been around 70 degrees Fahrenheit. There have been only four brief intervals where it deviated from this.

We are in one such interval now. Earth's temperature now is about 55 degrees.

It has been only 10,000 to 15,000 years since the most recent retreat of the Pleistocene glaciers, which began their advance 1.6 million years ago, and at the height of their most recent advance 18,000 years ago covered much of the northern hemisphere with a 2-mile-thick sheet of ice.

During the Ice Age, as it is commonly called, glaciers advanced and retreated across North America, Europe, and South America at least four times, averaging about 75,000 years per advance. Between advances, interglacial periods averaged about 50,000 years.

Two of the other periods of prolonged cold also coincided with glacial periods. One of these was during an ancient ice age at the boundary between the Silurian and Ordivician Period about 440 million years ago.

The other was a lesser ice age during the Carboniferous, which is the only other time in Earth's history that both temperature and carbon dioxide levels were similar to current conditions.

Our data tell us that the amount of carbon dioxide has increased by about 30 percent since the middle of the 19th century, with nearly half of it since 1970.

Our data tell us that in the same time period the average global temperature has risen likewise over the past two decades, with three of the four warmest years on record occurring 2002, 2003 and 2004.

On the other hand, geologic record for the past 600 million years does not show that there is a connection between carbon dioxide and global temperature.

We know that Earth's temperature has fluctuated only briefly in the past, and we know that throughout most of Earth's history the planet's temperature has been much warmer than it is today.

What we do not know is whether we are in an interglacial period or coming out of a glacial age. We don't know what will happen in the future. All we really know is that the world is getting warmer and that we are changing the composition of the atmosphere by adding carbon dioxide.

Michael Crichton's new book, "State of Fear" has already caused quite a bit of controversy, and it should, but it should also stimulate serious thought about our assumptions.

As sophisticated as we may be scientifically, and as successful as science has been in understanding, describing, and explaining natural phenomena, it appears that we may be in danger of becoming a society that relies on mysticism rather than on science.

Any statistician knows and so should any scientist, that correlation does not imply causation. The ancient Egyptians attributed the annual flooding of the Nile to the rising of the star, Sirius at sunset, assigning a causality to the correlation and evolving a society that worshiped of the star.

Let us hope that we do not fall prey to the same kind of misconceptions and take the wrong action, whatever it might be.