There is a widespread misconception that the increase in carbon dioxide caused by human activities will mostly result in a gradual increase in the temperature of the planet. However, consider just one well-established result: sea levels will rise significantly due to an increase in ocean temperature combined with melting of ice in Greenland and Antarctica. Even the rise of a few centimeters can make a big difference in low lying areas around the world, especially when storms cause onshore surges. In the United States, catastrophic floods are predicted for New Orleans and other areas in Louisiana, Texas and Florida (map below). World-wide, floods will first affect low-lying countries such as Bangladesh, The Netherlands and several Pacific island nations.
In addition to the overall warming trend for the world as a whole, detailed climate models predict extreme changes in local climates. The figure above illustrates the predictions for North America, valid for the present and near future. The models predict that the southwestern U.S will experience a general decrease in precipitation, exacerbating an already too-dry climate to the point where it will all become a desert.. For the central and eastern United States, in contrast, the main effect is expected to be an increase in rainfall and stormy weather -- resulting in increased flooding and other damage.
Even within one country, therefore, global climate change may result in increased rainfall in some areas, and decreased rainfall in others, and even increased temperatures in some seasons, lower in others. Some such effects are relatively easy to explain: The increase in severity of storms coming in from the Gulf, for example, is attributed to the fact that much more energy is available for storms when there is even a small increase in the sea surface temperature. Other reasons for extreme weather to occur during the process of significant global climate change are discussed in section 8.
Many changes predicted in the map above have probably already begun. There have recently been record storms in the Midwest and East, while many California central valley farmers are unable to plant because of lack of water. Glaciers and snow pack have been declining worldwide, and the arctic sea ice is retreating. The models all predict that the fastest warming will occur at the poles, and we are already seeing melting of the permafrost in northern latitudes.
Permafrost melting is not just a local problem: This melting will release additional methane into the atmosphere. Since methane is an even more potent greenhouse gas than carbon dioxide, the permafrost melting constitutes a potential positive feedback effect that is very dangerous.
Feedback loops and tipping points
This brings us to another level of prediction, based on the fact that the global weather system is a large non-linear feedback system. There are a number of both positive and negative feedback loops in the world's climate system, some with global effects. A positive feedback loop is one in which the effect of a change in a parameter, like the temperature or the CO2 level, is amplified. For this reason, the result of a positive feedback loop is not usually "positive," rather it is usually "bad." One example of a positive feedback loop involving permafrost melting is mentioned above.
Another example of a feedback loop in cold areas involves the fact that ice reflects nearly all of the sunlight that falls on it, which has a tendency to help keep the temperature low when ice covers the land or sea.. This is a feedback effect that tends to stabilize the climate during an ice age, "locking" the planet into a glacial period.
However, if increased temperatures do cause the ice to melt over ocean or land area during the summer, the water or land then exposed will absorb more of the light falling on it. This causes an overall increase in the heat absorbed. Depending on conditions, this can cause the global temperature to rise more, consequently less snow falls or less ice forms, providing a potential runaway.
There are also negative feedback loops in the climate system. Negative feedback loops operate to reduce the changes induced in a system by a parameter change, such as the carbon dioxide level. This results in an apparent stability in the system in spite of changes in CO2, so that the existence of a negative feedback loop sounds like it would be "good." One example of a negative feedback loop involves the fact that an increase in CO2 is expected to help plants grow faster, which results in some of the excess CO2 being taken back out of the atmosphere as it ends up being stored in the plants.
The most frightening aspect of climate change is that the existence of both negative and positive feedback loops in a nonlinear system can lead to abrupt changes in apparently stable states as one "forcing" parameter (e.g., CO2 level) changes. At first, the negative feedback loops minimize the change, giving the appearance of stability. As the forcing parameter increases, however, one of the positive feedback loops eventually overwhelms the stability of the system.
The system then can flip abruptly (and possibly catastrophically) into a new stable state, which may have very different local and global climate characteristics. The inhabitants may have little time to adjust. The state of the system at which such a flip in state occurs is sometimes called a "tipping point." Some have suggested that a global rise in temperature of only 1-2 degrees Centigrade may be enough to reach the first catastrophic tipping point.
In addition to the overall warming trend for the world as a whole, detailed climate models predict extreme changes in local climates. The figure above illustrates the predictions for North America, valid for the present and near future. The models predict that the southwestern U.S will experience a general decrease in precipitation, exacerbating an already too-dry climate to the point where it will all become a desert.. For the central and eastern United States, in contrast, the main effect is expected to be an increase in rainfall and stormy weather -- resulting in increased flooding and other damage.Even within one country, therefore, global climate change may result in increased rainfall in some areas, and decreased rainfall in others, and even increased temperatures in some seasons, lower in others. Some such effects are relatively easy to explain: The increase in severity of storms coming in from the Gulf, for example, is attributed to the fact that much more energy is available for storms when there is even a small increase in the sea surface temperature. Other reasons for extreme weather to occur during the process of significant global climate change are discussed in section 8.
Many changes predicted in the map above have probably already begun. There have recently been record storms in the Midwest and East, while many California central valley farmers are unable to plant because of lack of water. Glaciers and snow pack have been declining worldwide, and the arctic sea ice is retreating. The models all predict that the fastest warming will occur at the poles, and we are already seeing melting of the permafrost in northern latitudes.
Permafrost melting is not just a local problem: This melting will release additional methane into the atmosphere. Since methane is an even more potent greenhouse gas than carbon dioxide, the permafrost melting constitutes a potential positive feedback effect that is very dangerous.
Feedback loops and tipping points
This brings us to another level of prediction, based on the fact that the global weather system is a large non-linear feedback system. There are a number of both positive and negative feedback loops in the world's climate system, some with global effects. A positive feedback loop is one in which the effect of a change in a parameter, like the temperature or the CO2 level, is amplified. For this reason, the result of a positive feedback loop is not usually "positive," rather it is usually "bad." One example of a positive feedback loop involving permafrost melting is mentioned above.
Another example of a feedback loop in cold areas involves the fact that ice reflects nearly all of the sunlight that falls on it, which has a tendency to help keep the temperature low when ice covers the land or sea.. This is a feedback effect that tends to stabilize the climate during an ice age, "locking" the planet into a glacial period.
However, if increased temperatures do cause the ice to melt over ocean or land area during the summer, the water or land then exposed will absorb more of the light falling on it. This causes an overall increase in the heat absorbed. Depending on conditions, this can cause the global temperature to rise more, consequently less snow falls or less ice forms, providing a potential runaway.
There are also negative feedback loops in the climate system. Negative feedback loops operate to reduce the changes induced in a system by a parameter change, such as the carbon dioxide level. This results in an apparent stability in the system in spite of changes in CO2, so that the existence of a negative feedback loop sounds like it would be "good." One example of a negative feedback loop involves the fact that an increase in CO2 is expected to help plants grow faster, which results in some of the excess CO2 being taken back out of the atmosphere as it ends up being stored in the plants.
The most frightening aspect of climate change is that the existence of both negative and positive feedback loops in a nonlinear system can lead to abrupt changes in apparently stable states as one "forcing" parameter (e.g., CO2 level) changes. At first, the negative feedback loops minimize the change, giving the appearance of stability. As the forcing parameter increases, however, one of the positive feedback loops eventually overwhelms the stability of the system.
The system then can flip abruptly (and possibly catastrophically) into a new stable state, which may have very different local and global climate characteristics. The inhabitants may have little time to adjust. The state of the system at which such a flip in state occurs is sometimes called a "tipping point." Some have suggested that a global rise in temperature of only 1-2 degrees Centigrade may be enough to reach the first catastrophic tipping point.
DETAILS
The map was compiled from reports from a number of different sources, including publications of the United States Global Research Program and the Intergovernmental Panel on Climate Change. The blank map was derived from a classroom map supplied by Houghton Mifflin Harcourt.
Information on specific mechanisms underlying tipping points may be found in a recent Science Daily summary Tipping Elements in the Earth System.
There is a simple experiment that demonstrates how much the amount of energy absorbed from sunlight depends on the surface reflectivity. All you need is the sun, a magnifying glass, and a sheet of white paper. First darken an area of the paper about one inch square with an ordinary pencil. Then take the paper and glass into the sun, and focus the sun's rays to a bright spot on the paper. Compare the amount of time it takes to start the paper to smoke on a white area compared to the blackened area. It should take only few seconds for a dark area, and much longer (possibly never) for a white area.
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