The geological record certainly tells us we are overdue for one. And 5,000 years ago the Sahara was green, which is what happens in warm periods, as warmer seas give off more evaporation to fall as rain. Deserts are a feature of ice ages. Article below by Pierre Jutras
Carbon dioxide has been given a bad rap. The 1997 Kyoto Protocol identified carbon dioxide emissions and their effect on global climate as the main environmental threat to tackle. Environmental activists, such as Greenpeace, are also putting most of their energy into defeating the same beast. From a geologist's perspective, however, this could be seen as an interesting paradox. To help explain, here are a few common misconceptions about carbon dioxide and global warming.
1. Carbon dioxide is a pollutant.
Nothing could be further from the truth. It is, in fact, the "greenest" gas in our atmosphere, and the most essential ingredient for life itself. It has no odour, no colour and no ill effects whatsoever. All it does is nourish life and keep our climate warm. It is the primary and most essential nutrient at the very base of the food chain, as photosynthetic plants, algae and bacteria remove it from the atmosphere and hydrosphere to store it in their tissues. Along with water vapour, it keeps our planet away from the temperature extremes experienced daily by planetary bodies that are devoid of it, such as our own moon.
2. A lot of the carbon dioxide in our atmosphere originally came from fossil fuels.
This is also not true. All the carbon that is stored in fossil fuels originally came from the atmosphere and hydrosphere before being stored in organic tissues and carbonate rocks. If there were no processes for sending some of this carbon back to the atmosphere and hydrosphere, the latter reservoirs would long ago have been depleted in carbon due to organic activity, and life would have eventually ceased to exist.
3. High atmospheric levels of carbon dioxide are bad for ecosystems.
During life's long history, carbon dioxide levels have been continuously fluctuating, causing alternating periods of global warming (greenhouse ages) and global cooling (ice ages). During greenhouse ages, which are characterized by carbon dioxide levels several times higher than today's, life goes through tremendous expansion and diversification, whereas periods of low carbon dioxide levels, such as today's, are affected by severe extinctions.
4. Global warming will force deserts to increase in size.
The geological record says otherwise, as greenhouse ages are characterized by an absence or quasi-absence of desertic conditions, which are a feature of ice ages.
5. Global warming will cause hurricanes and other atmospheric turbulences to increase in energy and frequency.
Because hurricanes are caused by steep gradients in atmospheric pressure, and therefore temperature, this is very unlikely. A greenhouse Earth is characterized by moist and temperate conditions from the poles to the equator, with a much less significant latitudinal gradient in temperature than exists today.
6. Atmospheric carbon dioxide levels have never been so high.
In fact, on a geological time scale, atmospheric carbon dioxide levels have hardly ever been so low, and ecosystems are suffering greatly because of that. The last time carbon dioxide levels were so low, near the end of the Paleozoic era (about 250 million years ago), the Earth's biosphere went through its greatest extinction, as 90 per cent of Paleozoic species were gone by the beginning of the Mesozoic era (age of the dinosaurs). The last time that life went through a major expansion and diversification was during the Cretaceous period (135 million to 65 million years ago), when atmospheric carbon dioxide levels were more than six times those of today. Moreover, when life first started, around 3.8 billion years ago, carbon dioxide levels were hundreds of times higher than today's. Since then, most of the original carbon dioxide content of Earth's primitive atmosphere has been stored in carbonate rocks, coal, oil and gas.
7. We are now in a period of global warming.
This is only true on a short time scale, such as the past 500 years or so. It is already not true at the scale of 5,000 years, when Earth's climate was considerably warmer, and it is certainly not true at the scale of five million years, which takes us out of the current ice age. The main control on large-scale carbon dioxide fluctuations, which ultimately control climatic fluctuations, is plate tectonics. When global plate tectonics are dominated by continental collisions, leading to the formation of supercontinents, the erosional rates of calcium and magnesium from continental crust increase. This leads to an increase in carbonate deposition (limestone and dolostone), which forms the main long-term storage of carbon away from the atmosphere.
Due to this, the formation of the four supercontinents in Earth's history (Arctica, Rodinia, Pangea and today's "Afrikeurasia") was synchronous with the four major ice ages (Eoarchean, Eoproterozoic, late Paleozoic and Quaternary). When plate tectonics are dominated by continental drift, limy sediments are recycled into the Earth's mantle, and much of their carbon content is then sent back to the atmosphere via volcanism. These are times of high carbon dioxide levels, global warming, and life expansion and diversification.
We are now in the middle of the fourth ice age, and biodiversity has been shrinking very rapidly over the past two million years (i.e. since long before the time when anthropogenic activities became meaningful).
Due to orbital cycles, ice ages are affected by regular, second-order climatic fluctuations. We have gone through warm peaks for the three main types of orbital cycles over the past 5,000 years, and all these cycles are now on a cooling trend. It is predicted that ice sheets will start forming again in mid-latitudes in about 3,000 years, and that half of North America and Europe will be covered by kilometres of ice in 5,000 years. Hence, the present warming trend is just a small notch in an otherwise cooling trend.
In a nutshell, we are putting a lot of energy into preventing global warming, whereas the threat of global cooling should perhaps be our main concern. Who knows, maybe one day we will burn fossil fuels for the sole purpose of preventing global cooling. Geological history has proven that ecosystems thrive better with a higher carbon dioxide budget. Yet, we are trying really hard to keep them in their present state of starvation.
Is the current trend of global warming a good thing? Not necessarily. There are two sides to every coin. If there are winners, there are bound to be losers, too. For example, polar bears would have to drastically change their lifestyle on a greenhouse Earth.
We need, therefore, to better evaluate the general outcome of global cooling versus status quo, and versus global warming, before making drastic moves such as the Kyoto Protocol. The geological record states quite clearly that global warming is best for ecosystems in general, but what about humans specifically?
Because we rely so much on agricultural production, chances are that mostly good would come from global warming, as it would increase agricultural productivity in mid to high latitudes.
Yet, one major concern that remains is the rate of temperature increase. Changes that are too rapid can be harmful to ecosystems, even if they head in the right direction. However, it is the tendency of humanity to look at any change as intrinsically bad. There is this ingrained biblical attitude and belief that the Earth was a static Garden of Eden before humans came to mess it up. In fact, the Earth is always changing, has always been changing, and always will be changing. It is better to adapt to changes and try to mould them to our benefit, than to hopelessly try to maintain things in a static state.
For mankind, the main ill effect of global warming is the accompanying rise in sea level that is caused by the gradual melting and shrinking of the Greenland and Antarctica ice sheets. The transition from an ice age to a greenhouse age forces ecosystems to migrate inland and toward higher latitudes. If the rate is reasonable, they do this effortlessly.
However, this would cause major civil engineering problems for concrete monsters such as New York City, which cannot migrate as readily. This is, of course, a major concern and the main reason why decision makers usually view environmental changes as negative. For example, billions of dollars have been spent on trying to stabilize the Mississippi Delta, a naturally unstable system, just to make sure that cities like New Orleans maintain a controlled waterway and do not find themselves, instead, in the path of this continuously shifting waterway. When the people of Greenpeace rail against global warming, are they really concerned with the future of these concrete monsters? Is the global warming problem really a "green" concern?
I offer this message to environmentalists: Please, leave the carbon dioxide and global warming problem to urban and economic planners, and deal with real atmospheric pollutants instead, such as carbon monoxide, aerosols, chlorofluorocarbons, tropospheric ozone, volatile organic compounds and sulphur oxides.
Pierre Jutras is an associate professor of geology at Saint Mary's University in Halifax, Canada.
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