When we think about changes in the Earth's climate in the recent past, it is important to realize that we are currently in a unique interval in geological history. We are in the Great Ice Age. A time within which human beings evolved both biologically and culturally, and spread out throughout most part of the planet. Continental glaciations such as the Great Ice Age are rare events in the Earth's history. There was widespread glaciation 230 million years ago which affected the continents in the southern hemisphere. This was a time when a 'super continent' called Pangea dominated the southern hemisphere. Pangea consisted of two connected super continents called Gondwanaland and Laurasia which broke apart over time to form continents of the southern hemisphere (Gondwanaland) and northern hemisphere (Laurasia). Evidence for this early glacial period is found in rocks of glaciogenic origin of this time period in Africa, South America, Australia, India and Antarctica.
In our own 'backyard' between Sault Ste. Marie-Elliot Lake- Sudbury there is a group of sedimentary rocks which display an affinity to a significant glacial period which took place between 2.2 and 2.4 billion years ago. This group of rocks is known as the Huronian Supergroup and are thought to represent four separate cycles of glaciation and deglaciation. The Gowganda Formation, in particular, shows widepsread evidence of a glacial origin with the presence of 'drop' stones in finely layered mudstones. These 'drop' stones represent stones carried by icebergs which were dropped into deep water as the iceberg melted.
For most of geological history and in particular, the last 1 billion years, the Earth has been free of continental glaciation and lacked permanent polar ice caps. The Earth's climate, in turn, has been milder than in the last 40 million years. The typical climates of the past are similar to those of current low latitudes. The presence of liquid water in the form of rivers, streams, seas and oceans, is well preserved in rocks throughout geological history.
Using modern analytical techniques such as oxygen isotope geothermometry and various geochronological methods, it is possible to determine the temperature on land and the deep sea over the past 40-65 million years. Analyses of the shells of organisms show a decreasing trend in temperature. This decrease in temperature culminated in the development and expansion of polar and alpine ice caps about 3 million years ago. Evidence for this glaciation is found in the presence of ice-rafted cobbles and pebbles ('drop' stones) appearing in 3 million year old deep sea sediments, carried as far as 3000 kilometres from Antarctica. In addition, glacial tills in the Sierra Nevada, USA, have been dated at 3 million years old.
The curious thing about these glacial periods is that they have a cyclical nature. The cycles reflect glacial advances and glacial retreates ('interglacials'). This is represented in the stratigraphic sediment or rock record, and can also be mapped out to a high level of detail by geologists who specialize in this field of study. The glacial advances and retreats can be dated accurately using carbon 14 isotopic techniques for organic matter such as wood, peat, and bone. Volcanic ash and rock can provide older dates beyond the limits of Carbon 14 dating.
So far I've painted a picture of cooling temperatures, the developement and expansion of glacial ice caps, and the cyclical nature of glaciation (glacial-interglacial). How does one fit global warming into this picture of climate change? We are currently in an 'interglacial' cycle; glaciers have or have been retreating - it seems to be consistent with what one would expect. The question is whether this interglacial cycle is 'normal' or has it been influenced by anthropogenic activities? The follow up question is: what, if any, will anthropogenic activities have on the glacial-interglacial cycles?
The answers to these two questions can be very profound. Can anthropogenic activities affect this integlacial warming cycle to the extent that the Earth moves out of the Great Ice Age?
In reviewing my geology text published in 1971 the authors noted that:
"the magnitude of overall average yearly temperature differential between a normal and glacial climate is only 5 or 10 degrees centigrade."
They estimated that a drop in the order of 4-5 degrees C from the present mean annual temperature could cause a renewal of continental glaciation. The corollary would also be true. This means that the Earth has a sensitive thermal budget and is in a very critical temperature position in the solar system. It is important to note that the Earth has has not been glaciated for most of the geological record and so a stable thermal equilibrium has been present. This would suggest that thermal imbalances are restored likely due to the buffering capability of Earth's oceans. However, restoring thermal imbalances may come at a significant cost in terms of extinction of species and the gradual evolution of new life forms.
Some geologists think that coal beds were formed from low-lying equatorial forests during the time of the Permo-Carboniferous Ice Age (200-300 million years ago). As glaciers advanced, sea levels dropped and there was growth of these forests. As glaciers retreated there was a rise in sea level which drowned the equatorial forests and produced 'organic swamps' which were buried by mud, preserved and fossilized into the coal seams we observe today.
For the two major glacial periods during the last 400 million years, there is evidence that both the Earth's average temperature and carbon dioxide (CO2) concentration in the atmosphere was lower than non-glacial periods. The evidence is based on 'proxies' or indirect measurements of carbon dioxide derived from varying sources, such as biological entities in soil and sea water and from pores in fossil tree leaves. Although there is a wide range in the concentration of carbon dioxide for these proxies, the magnitude of the change is consistent with glacial and non-glacial events. The concentration of CO2 in the atmosphere is significant because it is the dominant 'greenhouse' gas. The higher the concentration of CO2 in the atmosphere, the greater the greenhouse heating effect that we would expect and vice-versa.
The geological record for the past 65 million years is much better preserved than that over 400 million years. This is due primarily to the presence of deep sea sediments which have been cored, dated, and analysed. These deep sea sediments can be found in various locations around the world in the deep oceans and represent a continuous stratigraphic record. Deep ocean temperatures based on oxygen isotopic composition of bottom dwelling organisms reveal a variable but decreasing trend over time. The CO2 proxy data has a wide variability but also displays a decreasing trend over time. The global decreasing temperature is in the 8-10 degree Centigrade range previously refered to, and culminate in the Great Ice Age of the Pleistocene Epoch.
The most significant and detailed information on paleotemperatures, carbon dioxide levels and other greenhouse gases comes from air trapped in ice cores obtained from Antarctica which can be dated back to 650 thousand years. The direct measurement of carbon dioxide (CO2), methane or natural gas (CH4), and nitrous oxide (N20) in trapped air bubbles show a consistent 'saw tooth' pattern with peaks reflecting warming periods (interglacial) and troughs reflecting glacial advances. These peaks and troughs reflect approximately 100,000 year glacial-interglacial cycles which correspond to periodic changes in parameters related to the orbit, tilt, and precession of the Earth as it rotates around the sun.
This cyclic relationship between climate and the chnging parameters of Earth's orbit were originally calculated in 1920 by M. Milankovich, a Yugoslavian meteorologist, and thus is referred to as the Milankovich Effect. However, glacial episodes have not occurred on a regular 100,000 year cycle over geological time, so there are other factors that need to be considered in order to push the Earth's thermal equilibrium past a 'tipping point' where orbital variations ('orbital forcing') play a significant role. These factors could include such thingss as the Earth's albedo, transparency, volcanic activity, and greenhouse gas content of the atmosphere.
The last glacial advance occurred about 20,000 years ago and is commonly referred to as the Wisconsinan Glacial in North America and Wurm Glacial in Europe. Within this 20,000 year period there was an overall retreat of the ide sheets from North America and Europe. In Canada, a large lake formed called Lake Agassiz, which extended over large areas of northwest Ontario, Manitoba, and into Saskatchewan and Wisconsin. As the continental glaciers retreated the water level of Lake Agassiz was lowered due to isostatic rebound of the crust, and left what is now Lake Winnipeg.
Within the Antarctic and Greenland ice cores, this warming trend (interglacial) is recorded by the increased carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in trapped air bubbles in the ice. Both the ice core data and direct atmospheric measurements show a dramatic increase in these greenhouse gas concentrations within the last 500 years and primarilly in the last 200 years since the industrial age began.
The range of greenhouse gas concentrations during most of the interglacial periods is consistent with the natural variability found over the past 650 thousand years, however, the last 200 years since the start of the industrial age show a very rapid increase which exceeds the natural variation. This rapid increase in the last 200 years is what has raised concerns regarding the impact of human activities on the thermal equilibrium of the Earth.
The current warming trend during the 20th Century appears unusual compared to the last 1000 years, but not in the longer geological time frame, where in fact higher temperatures have prevailed. It is the rate of warming that is anomalous, even in the longer geological context. Global warming during a glacial retreat is a gradual process taking about 5000 years. Most of the current rapid rise in global temperature has taken place in the last 50 years, raising the global temperature 4 to 5 degrees centigrade. If global temperatures continue to increase at the current rate over a period of time - say 200 years, then it will likely have a significant effect on the thermal equilibrium of the Earth, likely increasing the speed polar and alpine ice caps retreat and resulting in rapid changes in sea level and local climate.
The stabilization and decrease in greenhouse gas emissions, specifically carbon dioxide may provide the time needed for the natural buffering capability of various Earth processes, such as the natural buffering capability of the oceans, to begin to reduce the CO2 concentration in the atmosphere and thus stabilize the long-term temperature trend, and return to the more normal values for the current interglacial period.
As a geologist, I've tried to look at climate change and global warming within a geological context. The uniformitarian view is that 'the present is the key to the past', that is, the natural processes that we see happening today and in the recent past provide us with a way to understand what we see in the rocks and the stratigraphic record. Catastrophic changes are also part of the geological record and there is good eveidence for significant rapid changes in Earth's history. Continental drift tells us how continents changed position over time and how their continued movement will alter their position in the future. Similarly, it is possible to model past climate changes and predict climate changes into the future.
Most climate change models show carbon dioxide reaching a value of 700 ppm in the atmosphere by the year 2100, and then leveling off and staying close to that value until the year 3000. Projected global warming based on global climate models is expected to be between 1.2 degrees C and 4.1 degrees C. By the 31st century is expected to be in the range between 1.9 and 5.5 degrees C. These models assume that there will be no additional emissions of CO2 after the year 2100.
In these scenarios, the effect on glaciers and ice caps is significant. Models show a decrease in ice sheet volume over time such that after 1000 years only 40% the the Greenland Ice cap volume will remain; by the 31st century only 4% of the ice cap remains with a rise in sea level of 6-7 metres over time. There is paleoclimatic evidence that sea level was 4-6 metres above present levels during the last interglacial.
The key point in the modeling is that even if greenhouse gas emissions were stabilized at 700 ppm CO2, the effect of these emissions on global warming would continue for centuries to come. This is mainly due to the slow rate at which the processes operate which remove CO2 from the atmosphere (i.e. atmosphere-ocean gas transfer, chemical weathering, and biological processes like photosynthesis).
The main assumption in these models of climate change is that there will be a limit to CO2 emissions by the end of this century, that is, zero emissions by 2100 thereby limiting atmospheric CO2 to 700 ppm (about twice the current levels). This in fact may be a conservative estimate if the rate of reduction and sequestration of CO2 does not increase.
One of the more significant influences on CO2 emissions is the burning of fossil fuels, specifically the burning of natural gas, petroleum, and coal. An important concept regarding CO2 emissions based on fossil fuels is the Hubbert Peak Theory. This theory is named after and American geophysicist, M. King Hubbard, who developed a method of modeling petroleum production. The theory is that for any individual oil producing region or for the planet as a whole, the rate of petroleum production tends to follow a bell-shaped curve. This bell-shaped curve represent the increase, leveling off, and decrease in petroleum production over time, and has been verified for a number of oil producing regions such as the USA, Mexico, Norway, and the world. The curves vary for other fossil fuels, but essentially have the same shape over different life spans.
Based on production data from all oil producing countries except OPEC and the former Soviet Union, peak oil production was reached in 2004. The implication of the Hubbard Peak Theory is that fossil fuels are a non-renewable resource and, as such, by 2100 the cost of extraction and environmental rehabilitation will be extraordinarily high to the point where renewable forms of energy will be needed to drive industry. A modeling date of 2100 is considered reasonable, since whether by political and social will or necessity, CO2 emissions will begin to stabilize at around 700 ppm.
Climate change is not new, but we are clearly having an impact on the normal interglacial cycle. Much of the population and the elected officials are both fatalistic and in denial regarding these changes. The real question that needs to be addressed is: what is each individual going to do to help make a better world for their grandchildren?
It is not a question of good science - the level of knowledge regarding past climate and glaciation is well established. Additional work will continue to add to this body of knowledge. It is not a question of what side you are on - the industrialist or the environmentalist; the issue is a-political. Just because I am a geologist and explore for minerals does not mean that I cannot agree with climate change and global warming. In fact, it is precisely because I have this background that I come to these views.
The Earth will continue to change; it has in the past and it will in the future. The question is how long will we be around to see these changes? Homo Sapiens can easily become an extinct species by the time continental glaciers once again begin their slow trek across the land - or maybe not?
The most significant and detailed information on paleotemperatures, carbon dioxide levels and other greenhouse gases comes from air trapped in ice cores obtained from Antarctica which can be dated back to 650 thousand years. The direct measurement of carbon dioxide (CO2), methane or natural gas (CH4), and nitrous oxide (N20) in trapped air bubbles show a consistent 'saw tooth' pattern with peaks reflecting warming periods (interglacial) and troughs reflecting glacial advances. These peaks and troughs reflect approximately 100,000 year glacial-interglacial cycles which correspond to periodic changes in parameters related to the orbit, tilt, and precession of the Earth as it rotates around the sun.
This cyclic relationship between climate and the chnging parameters of Earth's orbit were originally calculated in 1920 by M. Milankovich, a Yugoslavian meteorologist, and thus is referred to as the Milankovich Effect. However, glacial episodes have not occurred on a regular 100,000 year cycle over geological time, so there are other factors that need to be considered in order to push the Earth's thermal equilibrium past a 'tipping point' where orbital variations ('orbital forcing') play a significant role. These factors could include such thingss as the Earth's albedo, transparency, volcanic activity, and greenhouse gas content of the atmosphere.
The last glacial advance occurred about 20,000 years ago and is commonly referred to as the Wisconsinan Glacial in North America and Wurm Glacial in Europe. Within this 20,000 year period there was an overall retreat of the ide sheets from North America and Europe. In Canada, a large lake formed called Lake Agassiz, which extended over large areas of northwest Ontario, Manitoba, and into Saskatchewan and Wisconsin. As the continental glaciers retreated the water level of Lake Agassiz was lowered due to isostatic rebound of the crust, and left what is now Lake Winnipeg.
Within the Antarctic and Greenland ice cores, this warming trend (interglacial) is recorded by the increased carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in trapped air bubbles in the ice. Both the ice core data and direct atmospheric measurements show a dramatic increase in these greenhouse gas concentrations within the last 500 years and primarilly in the last 200 years since the industrial age began.
The range of greenhouse gas concentrations during most of the interglacial periods is consistent with the natural variability found over the past 650 thousand years, however, the last 200 years since the start of the industrial age show a very rapid increase which exceeds the natural variation. This rapid increase in the last 200 years is what has raised concerns regarding the impact of human activities on the thermal equilibrium of the Earth.
The current warming trend during the 20th Century appears unusual compared to the last 1000 years, but not in the longer geological time frame, where in fact higher temperatures have prevailed. It is the rate of warming that is anomalous, even in the longer geological context. Global warming during a glacial retreat is a gradual process taking about 5000 years. Most of the current rapid rise in global temperature has taken place in the last 50 years, raising the global temperature 4 to 5 degrees centigrade. If global temperatures continue to increase at the current rate over a period of time - say 200 years, then it will likely have a significant effect on the thermal equilibrium of the Earth, likely increasing the speed polar and alpine ice caps retreat and resulting in rapid changes in sea level and local climate.
The stabilization and decrease in greenhouse gas emissions, specifically carbon dioxide may provide the time needed for the natural buffering capability of various Earth processes, such as the natural buffering capability of the oceans, to begin to reduce the CO2 concentration in the atmosphere and thus stabilize the long-term temperature trend, and return to the more normal values for the current interglacial period.
As a geologist, I've tried to look at climate change and global warming within a geological context. The uniformitarian view is that 'the present is the key to the past', that is, the natural processes that we see happening today and in the recent past provide us with a way to understand what we see in the rocks and the stratigraphic record. Catastrophic changes are also part of the geological record and there is good eveidence for significant rapid changes in Earth's history. Continental drift tells us how continents changed position over time and how their continued movement will alter their position in the future. Similarly, it is possible to model past climate changes and predict climate changes into the future.
Most climate change models show carbon dioxide reaching a value of 700 ppm in the atmosphere by the year 2100, and then leveling off and staying close to that value until the year 3000. Projected global warming based on global climate models is expected to be between 1.2 degrees C and 4.1 degrees C. By the 31st century is expected to be in the range between 1.9 and 5.5 degrees C. These models assume that there will be no additional emissions of CO2 after the year 2100.
In these scenarios, the effect on glaciers and ice caps is significant. Models show a decrease in ice sheet volume over time such that after 1000 years only 40% the the Greenland Ice cap volume will remain; by the 31st century only 4% of the ice cap remains with a rise in sea level of 6-7 metres over time. There is paleoclimatic evidence that sea level was 4-6 metres above present levels during the last interglacial.
The key point in the modeling is that even if greenhouse gas emissions were stabilized at 700 ppm CO2, the effect of these emissions on global warming would continue for centuries to come. This is mainly due to the slow rate at which the processes operate which remove CO2 from the atmosphere (i.e. atmosphere-ocean gas transfer, chemical weathering, and biological processes like photosynthesis).
The main assumption in these models of climate change is that there will be a limit to CO2 emissions by the end of this century, that is, zero emissions by 2100 thereby limiting atmospheric CO2 to 700 ppm (about twice the current levels). This in fact may be a conservative estimate if the rate of reduction and sequestration of CO2 does not increase.
One of the more significant influences on CO2 emissions is the burning of fossil fuels, specifically the burning of natural gas, petroleum, and coal. An important concept regarding CO2 emissions based on fossil fuels is the Hubbert Peak Theory. This theory is named after and American geophysicist, M. King Hubbard, who developed a method of modeling petroleum production. The theory is that for any individual oil producing region or for the planet as a whole, the rate of petroleum production tends to follow a bell-shaped curve. This bell-shaped curve represent the increase, leveling off, and decrease in petroleum production over time, and has been verified for a number of oil producing regions such as the USA, Mexico, Norway, and the world. The curves vary for other fossil fuels, but essentially have the same shape over different life spans.
Based on production data from all oil producing countries except OPEC and the former Soviet Union, peak oil production was reached in 2004. The implication of the Hubbard Peak Theory is that fossil fuels are a non-renewable resource and, as such, by 2100 the cost of extraction and environmental rehabilitation will be extraordinarily high to the point where renewable forms of energy will be needed to drive industry. A modeling date of 2100 is considered reasonable, since whether by political and social will or necessity, CO2 emissions will begin to stabilize at around 700 ppm.
Climate change is not new, but we are clearly having an impact on the normal interglacial cycle. Much of the population and the elected officials are both fatalistic and in denial regarding these changes. The real question that needs to be addressed is: what is each individual going to do to help make a better world for their grandchildren?
It is not a question of good science - the level of knowledge regarding past climate and glaciation is well established. Additional work will continue to add to this body of knowledge. It is not a question of what side you are on - the industrialist or the environmentalist; the issue is a-political. Just because I am a geologist and explore for minerals does not mean that I cannot agree with climate change and global warming. In fact, it is precisely because I have this background that I come to these views.
The Earth will continue to change; it has in the past and it will in the future. The question is how long will we be around to see these changes? Homo Sapiens can easily become an extinct species by the time continental glaciers once again begin their slow trek across the land - or maybe not?
