資料紹介
Global Warming
Greenhouse Gases and Climate
Is the climate becoming warmer and warmer?
According to the National Academy of Sciences, the Earth's surface temperature has risen by about 1 degree Fahrenheit in the past century, with accelerated warming during the past two decades. There is new and stronger evidence that most of the warming over the last 50 years is attributable to human activities. Human activities have altered the chemical composition of the atmosphere through the buildup of greenhouse gases – primarily carbon dioxide, methane, and nitrous oxide. The heat-trapping property of these gases is undisputed although uncertainties exist about exactly how earth's climate responds to them. (source:US-EPA)
Global temperature trend Note that these are surface temperatures and mostly overland. The temperature in upper levels may be different, even reversed.
Source: UK Met Office
What cause the temperature of the atmosphere to go up?
There are many possible mechanisms that can cause the warming of the atmosphere, for example:
Natural variation – the climate becomes warmer by internal chaotic dynamics of the earth-atmosphere system (that is, no external influence).
Solar activity – either direct increase of solar energy output or indirect “trigger” mechanisms due to solar activity (though nobody knows how) may cause the surface temperature to go up.
Greenhouse effect – increasing “greenhouse” gases such as CO2, CH4, NO, CFC,…etc. (actually H2O is very efficient, too, but at
資料の原本内容
Global Warming
Greenhouse Gases and Climate
Is the climate becoming warmer and warmer?
According to the National Academy of Sciences, the Earth's surface temperature has risen by about 1 degree Fahrenheit in the past century, with accelerated warming during the past two decades. There is new and stronger evidence that most of the warming over the last 50 years is attributable to human activities. Human activities have altered the chemical composition of the atmosphere through the buildup of greenhouse gases – primarily carbon dioxide, methane, and nitrous oxide. The heat-trapping property of these gases is undisputed although uncertainties exist about exactly how earth's climate responds to them. (source:US-EPA)
Global temperature trend Note that these are surface temperatures and mostly overland. The temperature in upper levels may be different, even reversed.
Source: UK Met Office
What cause the temperature of the atmosphere to go up?
There are many possible mechanisms that can cause the warming of the atmosphere, for example:
Natural variation – the climate becomes warmer by internal chaotic dynamics of the earth-atmosphere system (that is, no external influence).
Solar activity – either direct increase of solar energy output or indirect “trigger” mechanisms due to solar activity (though nobody knows how) may cause the surface temperature to go up.
Greenhouse effect – increasing “greenhouse” gases such as CO2, CH4, NO, CFC,…etc. (actually H2O is very efficient, too, but at present it is assumed to be in steady state).
The greenhouse effect is presently thought to be the most likely cause of the global warming and is the focus of our discussion here.
The real greenhouse
The (Atmospheric) Greenhouse Effect
Examples of greenhouse gases: H2O, CO2, CH4, CFC.
Currently, CO2 is the main suspect of causing the global warming since the 20th century because combustion of fossil fuel naturally injects CO2 into the atmosphere and it has increased dramatically since last century.
Remember this chart?
In the atmosphere, gases such as H2O, CO2, CH4, CFC, etc., are capable of absorbing the terrestrial radiation (peaking at infrared wavelength) and re-radiate in all directions. Thus part of the re- radiation is sent back to the surface. This means that in the presence of these gases, the atmosphere will be warmer than without them. These gases thus play the role of glass panels in a greenhouse. Hence the name greenhouse gases. It is therefore reasonable to expect that increasing concentrations of greenhouse gases will cause warming in the atmosphere.
Currently, CO2 is the main suspect of causing global warming because combustion of fossil fuel naturally injects CO2 into the atmosphere. Whereas other natural processes also inject CO2, the industrial combustion process seems to play a significant role in the concentration increase.
Atmospheric Carbon Dioxide
This chart shows a steady increase of CO2 concentration in the last five decades. Although this chart is based on Mauna Loa’s data, the same trend has been found in many other places.
Charles Keeling had kept track of the atmospheric concentration of CO2 since ’50s. This chart shows a steady increase of CO2 concentration (in addition to the annual fluctuation) in the last five decades. Although this chart is based on Mauna Loa’s data, the same trend has been found in many other places.
South Pole and Barrow, Alaska, show the same trend as Hawaii
How is the CO2 increase connected to the global warming?
Physically, via the greenhouse effect.
The connection is usually made via the use of a climate model.
Control run versus scenarios.
If the scenario run results show warmer surface condition than the control, then it is plausible to suspect that the increasing CO2 concentration in the atmosphere may cause warming.
Through the greenhouse effect, of course.
The connection is usually made via the use of a climate model. A climate model is usually a kind of the atmospheric general circulation ...
