Global Warming: Armageddon or Bust? Some Scientists See the Possibility of Global Warming as the Precursor to a Global Armageddon, to Others It Is Merely Hype; the Truth Lies Somewhere in Between

Carbon dioxide, generally believed to be the most important greenhouse gas and climate modifier, is today the centerpiece of a heated political and scientific debate. In its most polarized form, one side maintains that is the principal driver of climate, and the sequence of events is higher equals global warming equals climate change equals disaster. Based on this scenario, the burning of fossil fuels and deforestation will inexorably lead to global warming, with the latest Intergovernmental Panel on Climate Change models projecting an average 1.5 to 5.5 degree Celsius temperature rise by the year 2100. Environmental Armageddon is an inevitable consequence of the above equation. The opposing view claims that the role of anthropogenic on climate has not been proved, and that there is, therefore, no need for the large expenditures necessitated by the emission-curtailment quotas, such as those mandated by the Kyoto protocol. As is usually the case with contenuous matters, the reality is likely in between, and the polarization arises mostly from two issues: (1) poor understanding of past variations in the carbon cycle and climate that must be taken into account as a baseline for any superimposed human impact, and (2) the uncertainties inherent in the climate models. This essay will deal mostly with the first subject, the carbon cycle, from the perspective of a geologist, contemplating it at time scales ranging from billions of years to the human life span. This perspective is essential, because events on progressively shorter time scales are embedded in, and constrained by, the evolution of the background on longer time scales. In terms of the second issue, the uncertainties inherent in the climate models, the admirable progress achieved by climate modeling must be acknowledged, but many serious pitfalls, such as the role of clouds, or the couplings to the oceanic and particularly the terrestrial biosphere (land plants), remain to be resolved. Considering that theoretical cooling by the clouds alone may potentially exceed, by up to 7.5 times, (1) the warming impact of the greenhouse gases, such concerns should be given due consideration and resolved prior to any definitive claims based on the climate scenarios. On the issue of modeling, I will restrict myself solely to the role of land plants in the carbon cycle because of their potential impact on the C[O.sub.2] sinks debate, which was the cause of failure of the Hague summit and a bone of contention during the Bonn meeting. Life, Water and the Carbon Cycle The story of the carbon cycle is essentially the story of life. Carbon and water are the fundamental building blocks of living things and the propagation of life is accomplished via continuous exchange of these two constituents with the atmosphere and hydrosphere (ocean and water bodies on land), such interactions being termed the water and the carbon cycle. While other cycles, such as those of nitrogen and phosphorus, are also involved, they are of lesser importance for the climate issues discussed here. In order to understand the role of atmosphere, water, and life for climate evolution in the geologic past, it is essential to study the ancient examples. Yet, we have no unequivocal samples of ancient waters, and the oldest samples of the ancient atmospheres are only about 420,000-year-old bubbles of air that were frozen into Antarctic ice at the time of its formation. The situation is somewhat better with the remnants of life, since mineralized shells go back to about 545 million years, and the impressions of living things, algae and bacteria, have been found in western Australia in rocks as old as 3.5 billion years. (2) Soft body tissues, altered by temperature and pressure, referred to as kerogen, have been found in still older rocks approaching 4 billion years. This is remarkable, because the oldest rocks ever recovered, found near Yellowknife in northwestern Canada, (3) are of about the same age. …

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