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Global Atmospheric and Surface Temperatures
The first thing to note is that there are a multitude of different temperatures for the atmosphere at any one time. There is the near-surface temperatures that are measured by thermometers at weather stations. There are also the temperatures at different levels of the atmosphere such at the 500 millibar pressure level which roughly represents the vertical midpoint of the atmosphere. Such temperatures are recorded using balloons and radiosonde devices. Temperature generally decreases with altitude up to a point, called the tropopause, and then above that increases with altitude. The part of the atmosphere in which temperature decreases with altitude is called the troposphere and the part in which temperature increases with altitude is called the stratosphere. Satellite devices can measure the average temperature of the entire atmosphere.
The theory of the greenhouse effect says that increased amounts of greenhouse gases should warm the troposphere. The near-surface temperatures have been increasing. Here are two depictions of the record of global surface temperature.(Anomaly in climatology just means the difference between a temperature at one point in time and the average temperature over some interval of time.)
Part of the increase in surface temperature is due to the Heat Island Effect. The more of the increase in the recorded temperatures which is attributed to the heat island effect the less that is attributable to global warming. There are other more subtle possible influences on the temperature record. The glass in glass thermometers slowly shrinks over time. This leads to higher readings of temperature. During the late 1930's and early 1940's the thermometers in the weather stations were not being replaced as regularly as had been before. This was due to the economic and political turmoil of the times. When World War II was over the old thermometers were replaced and this could have led to decreases in the measured temperatures over their previous values. It is alleged that the recorded temperatures in the areas such as the United States, Great Britain, Australia and New Zealand are not showing increases. These are the areas where the readings are more accurate. The increases come in Third World countries where the temperature readings may be less accurate. It is also alleged that the global temperature increases in the late 1990's are correlated with Russia closing down hundreds of weather stations in the arctic and high latitude regions for budgetary reasons.
The satellite average temperatures for the atmosphere do not show an upward trend but that data only goes back to 1979.
The form in which the data is plotted has a great influence upon the viewers' perception the significance of the data. Consider the data in terms of the year-to-year change in temperature.
The near-surface data shows an increase over time primarily from increases in winter temperatures and night-time temperatures. Daytime and summer temperatures do not show an upward trend. The theory of the greeenhouse effect would call for an increase in the summertime and also in the daytime.
Below are given the temperature records by latitude for the Northern Hemisphere.
The temperature record for the Southern Hemisphere is given below.
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