Ice ages are hard to think about. They happen over geologic time which may be easy for the average geologist to think about, but not so for the average human. The time scale is the major stumbling block. Let’s think about that a little. First, recall that the Earth was formed about the same time as the our Sun–4.8-5 billion years ago. It took the Earth many millions of years to form the Moon, cool down and form solid (non-molten) rocks. Then the Earth’s vaporized water, still in the atmosphere, gradually rained down, forming the oceans, rivers, lakes and streams.
Gradually primitive single cell organisms formed living in a primitive atmosphere composed of very little if any oxygen. Then about 2-2.5 billion years ago simple organisms acquired the biological machinery to do photosynthesis: They could use carbon dioxide and sunlight to make simple bio-molecules necessary to live. In the process these organisms captured the energy of the sun to make complex bio-molecules from the carbon in the carbon dioxide and also found ways to integrate nitrogen, phosphorus, oxygen and other elements but expelled molecular oxygen as a by-product, allowing the atmosphere over time to increase significantly in molecular oxygen concentrations. Gradually as oxygen concentrations in the atmosphere increased, nearly all of the simple single cell organisms that had been present on the planet died. They found oxygen to be toxic. Many survived and evolved, but they had to go underground or into places where the toxic oxygen gas could not follow. This transition going from mostly organisms intolerant of oxygen to organisms tolerant to oxygen lasted another billion years or so until we get to the point 700-900 million years ago when the composition of the atmosphere of the Earth was about the same as it is presently.
Many species populated the Earth. Many died off and were succeeded by others. There have been several major species die offs in the Earth’s history, the first being the one when oxygen-intolerant species were replaced by oxygen tolerant species as oxygen filled the atmosphere.
Finally, only a few million years ago humans appeared. After about a million years of living on the edge, they found out how to survive and gradually became the dominant species on the planet. It took us a very long time to get here and once we got here it took a while to get things under control. But to put that in perspective let’s think of the entire history of the planet as having occurred over one day’s duration. Our simple primitive single cell friends would have appeared after about 5-6 hours, but then would have largely died away after 12 hours or so. The more complex, and in some cases multi-cellular, photosynthetic organisms would have set the stage for more complicated organisms by providing them with an oxygen atmosphere similar to what we have now. This was accomplished after 19-20 hours. And, finally our ancestors would have arrived only about 43 second ago and then gotten control of the place about 22 seconds later.
Although ice ages have been happening for over 2 billion years we’re just going to think about those that have been happening in the last 2-3 million years. It’s a bit anthropocentric, but after all those are the ice ages that have been happening recently (in planetary terms). We’ve had ice ages fairly regularly every 100,000 years or so and they’ve lasted 40,000 or more years in most cases. Then we come out of it into a warming period that may last 30-50,000 years before we start reentering the next cycle. Only in the last century have we developed any clear grasp of how this periodic behavior occurs.
The major reason for the comings and goings of ice ages may be what is called the Milankovich Cycles. These have to do with regular deviations in the orbital motions of the planet. These occur in 21,000 to 40,000 year cycles. Basically each changes the angles of the planet to the Sun–expanding both spring and and summer primarily in the Northern Hemisphere. Each year the planet will warm or get cooler slightly more or less. These are very small changes year by year but over a thousands of years can add up to warming or cooling.
The other signals for ice age initiation have been suggested to be variations in Tectonic Plate motions, but these would likely be better applied to ice ages occurring long before 2-3 million years ago where there were major changes in the positions of the tectonic plates in respect to the position of the equator and in the positions of developing ice sheets.
Carbon dioxide concentrations increase from about 180 ppm during the ice age to about 290 ppm during the warming cycle. This begins to happen after warming is initiated and may simply reflect the slow increase in carbon dioxide in the atmosphere from biomass decay starting as temperatures increase over the warming planet. These carbon dioxide concentrations have been suggested as warming signals as the planet responds to the elevated carbon dioxide as a greenhouse gas. Yet, the idea that carbon dioxide and other so-called greenhouse gases were associated with the warming of the planet is a 19th century idea not very well supported by modern ideas of thermal physics.
Still, burning all of our remaining fossil fuels over the next century or two will elevate atmospheric carbon dioxide concentrations substantially and these will likely produce major effects on the planet even if they are not primarily felt as increased warming of the planet. Major increases in ocean acidity from further elevated carbon dioxide will require significant adaptation of ocean life potentially interrupting the planet’s food chain. On shore, significant additional increases in carbon dioxide concentrations as we burn our remaining fossil fuels, at least contributes to accelerated increases in both underground and above ground biomass. All plant’s from small to large will benefit.
Nevertheless, we need to remember that we are somewhere near the midpoint between ices ages, and we are still in a warming phase. If the ice ages continue with the same regularity as in the recent past, the next ice age may still be 30,000 to 50,000 years distant. Surface ice in the Arctic is slowly disappearing, and for a while overall warming may predominate as the planet continues to try to cool it tropical zones in new ways against accelerated warming in the northern regions. Ocean warming and cooling currents may be affected in major ways, creating novel weather effects where they did not previously exist. In the next century or more, whether we burn all of the remaining fossil fuel or not, we will likely lose all or most of the Greenland glacial ice to the sea as well as the large western Antarctic ice shelf. These events alone will cause major sea level increases. That will affect global coastal communities, many of which may not be saved by even the most heroic efforts.
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Richard A. Hudson is a writer, reader and blogger committed to exercise, proper nutrition and health. He’s interested in politics, economics, alternative energy, gardening and sustainability and has written brief essays on many of these topics on his bloghttp://richlynne.wordpress.com. Despite his generally positive and optimistic views about globalization, he wonders whether we will survive current destructive forces that increasingly promote warfare among political and social classes. He is also beginning to think about the declining influence of the know-it-all baby boomer generation just as the next generation born in the 60s begins to slowly stumble into a dominant position in the U.S.
He received a Ph.D. in organic chemistry from the University of Chicago (1966) and subsequently spent 42 years in academics, gradually developing all sorts of interests well beyond his basic training. He ended his academic career in 2008, having published about 100 scientific papers, reviews and commentaries. In his last several years in the academy, his role as Dean of the Graduate School afforded him many opportunities to interact with students from all over the world seeking graduate degrees.