Early research on the “greenhouse effect” started in the late 19th century with work by Joseph Fourier. The further study and subsequent understanding and description of the process has enabled scientists to understand our current climactic warming trend, and hopefully, provide enough advance notice and warning to head off serious climate problems in the future.
As the Earth receives a constant supply of energy from the sun, the shorter wavelength energy easily penetrates the atmosphere and is either reflected back into space by things like glaciers, or absorbed by the Earth’s surface. The surface radiates this energy back towards space but with longer wavelengths. Carbon dioxide, methane, and other heat trapping gasses absorb longer wavelength radiation and reradiate some of the energy they absorb back toward the Earths surface, warming the planet. Without this, the earth would be about 70 degrees colder than it is. By comparison, a drop in aggregate temperatures of around 7 degrees caused the Great Ice Age. Venus, the closest planet to the Earth, has an atmosphere that is almost entirely made up of CO2 and methane, and surface temperatures reach 900 degrees as a result.
The concentrations of CO2 in the Earth’s atmosphere have varied considerably over the millennia, from around 180 ppm during cold, glacial times to around 300 ppm during warmer interglacial periods. In the twentieth century, however, concentrations have risen well above these levels and done so very rapidly. In preindustrial times there was around 280 ppm CO2 in the atmosphere, now the level has reached 370 ppm and climbing. A graph of global aggregate temperatures during the same period shows them following greenhouse gas concentrations, almost step for step, with the fastest rise in the last twenty years.
In addition to changing the concentrations of heat trapping gasses, there are two other factors that can affect climate temperatures. First, changes in the total amount of energy reaching the Earth. This has had some affect on climates in the past, but the total variation is relatively small, about .1% over an 11 year cycle. This does not appear to be a factor in current warming as we are in a period of very low sunspot activity, though it would be expected to increase in the near future. Secondly, is to change the reflectivity, or albedo, of the surface of the Earth. This can be brought about by a loss of ice sheet as glaciers recede. We are experiencing this on a global scale, and it tends to exacerbate the warming trend. As the increase in CO2 warms the climate, ice melts and reflects less energy, warming it further in a positive feedback loop.
Concerns that the increased CO2 might not be man made, and may instead be naturally occurring, are misguided. Carbon has two common isotopes in the atmosphere, C12 and C13. The carbon in plants, and so in fossil fuels, is almost exclusively C12. Other naturally occurring sources of CO2 are primarily C13. As the concentrations of CO2 in the atmosphere have increased, the ratios of C12 to C13 have gone up accordingly.
Over the centuries, the climate has had many periods of warming and cooling, each with its own cause for starting and ending, and almost all are very well understood by climate scientists. This time the cause is a buildup of heat trapping gasses in the atmosphere causes by human activity. Most estimates indicate that 75% of the buildup is caused by the burning of fossil fuels and the other 25% by deforestation. As levels of greenhouse gasses continue to increase, the effects of the increased heat in the atmosphere will become more and more noticeable. It is a path we continue down at our peril.
At current rate of increase, it has been estimated that sea levels will rise around one meter over the next century. In fact, a panel of scientists at MIT compiled 16 different plausible projections that ranged from .02 meters to 6 meters. A rise of one meter, while derided in some American press as just enough to submerge a beach chair, will submerge 17% of Bangladesh, virtually all of the Maldives, and displace millions of people, generally the ones least able to move and adapt. While the number of named storms has increased 40% since the 1950’s (which was a level considered extreme at the time) there has not been a detectable increase in the intensity of the storms yet, although scientists generally expect that to change. Most prediction indicate we can expect an increase in major weather events of all kinds and a general disruption in weather patterns ( with consequent problems for agriculture) as we continue to alter the chemical composition of an atmosphere that we have been able to depend on for thousands of years.
Early research on the “greenhouse effect” started in the late 19th century with work by Joseph Fourier. The further study and subsequent understanding and description of the process has enabled scientists to understand our current climactic warming trend, and hopefully, provide enough advance notice and warning to head off serious climate problems in the future.
As the Earth receives a constant supply of energy from the sun, the shorter wavelength energy easily penetrates the atmosphere and is either reflected back into space by things like glaciers, or absorbed by the Earth’s surface. The surface radiates this energy back towards space but with longer wavelengths. Carbon dioxide, methane, and other heat trapping gasses absorb longer wavelength radiation and reradiate some of the energy they absorb back toward the Earths surface, warming the planet. Without this, the earth would be about 70 degrees colder than it is. By comparison, a drop in aggregate temperatures of around 7 degrees caused the Great Ice Age. Venus, the closest planet to the Earth, has an atmosphere that is almost entirely made up of CO2 and methane, and surface temperatures reach 900 degrees as a result.
The concentrations of CO2 in the Earth’s atmosphere have varied considerably over the millennia, from around 180 ppm during cold, glacial times to around 300 ppm during warmer interglacial periods. In the twentieth century, however, concentrations have risen well above these levels and done so very rapidly. In preindustrial times there was around 280 ppm CO2 in the atmosphere, now the level has reached 370 ppm and climbing. A graph of global aggregate temperatures during the same period shows them following greenhouse gas concentrations, almost step for step, with the fastest rise in the last twenty years.
In addition to changing the concentrations of heat trapping gasses, there are two other factors that can affect climate temperatures. First, changes in the total amount of energy reaching the Earth. This has had some affect on climates in the past, but the total variation is relatively small, about .1% over an 11 year cycle. This does not appear to be a factor in current warming as we are in a period of very low sunspot activity, though it would be expected to increase in the near future. Secondly, is to change the reflectivity, or albedo, of the surface of the Earth. This can be brought about by a loss of ice sheet as glaciers recede. We are experiencing this on a global scale, and it tends to exacerbate the warming trend. As the increase in CO2 warms the climate, ice melts and reflects less energy, warming it further in a positive feedback loop.
Concerns that the increased CO2 might not be man made, and may instead be naturally occurring, are misguided. Carbon has two common isotopes in the atmosphere, C12 and C13. The carbon in plants, and so in fossil fuels, is almost exclusively C12. Other naturally occurring sources of CO2 are primarily C13. As the concentrations of CO2 in the atmosphere have increased, the ratios of C12 to C13 have gone up accordingly.
Over the centuries, the climate has had many periods of warming and cooling, each with its own cause for starting and ending, and almost all are very well understood by climate scientists. This time the cause is a buildup of heat trapping gasses in the atmosphere causes by human activity. Most estimates indicate that 75% of the buildup is caused by the burning of fossil fuels and the other 25% by deforestation. As levels of greenhouse gasses continue to increase, the effects of the increased heat in the atmosphere will become more and more noticeable. It is a path we continue down at our peril.
At current rate of increase, it has been estimated that sea levels will rise around one meter over the next century. In fact, a panel of scientists at MIT compiled 16 different plausible projections that ranged from .02 meters to 6 meters. A rise of one meter, while derided in some American press as just enough to submerge a beach chair, will submerge 17% of Bangladesh, virtually all of the Maldives, and displace millions of people, generally the ones least able to move and adapt. While the number of named storms has increased 40% since the 1950’s (which was a level considered extreme at the time) there has not been a detectable increase in the intensity of the storms yet, although scientists generally expect that to change. Most prediction indicate we can expect an increase in major weather events of all kinds and a general disruption in weather patterns ( with consequent problems for agriculture) as we continue to alter the chemical composition of an atmosphere that we have been able to depend on for thousands of years.
