The concentration of the atmosphere’s main greenhouse gases specifically, carbon
dioxide, methane, nitrous oxide, and water vapor, have increased significantly during the
industrial age. These high concentrations are predicted to continue in the atmosphere for
thousands of years to come. This increase in specially carbon dioxide, increases the
infrared energy taken in by the atmosphere, and warming the earth’s surface. The Global
mean temperature over the past 150 years has risen between 0.3 degrees C and 0.6
degrees C. Climate changes that have been predicted are based on the continual rise in
Green House Gases. These changes include changes in: increase in mean surface air
temperature, increase in global mean rates of precipitation and evaporation, rising sea
level, and changes in the biosphere.
There are many causes to the rise in Green House Gases in the atmosphere. The
rise in carbon dioxide in the atmosphere is largely related to the combustion of fossil fuels
and cement production (Hansen). The increase in methane is do to rice cultivation, animal
husbandry, biomass burning, and landfills (Kattenberg). Nitrous oxide is on the rise
because of industrial sources like adipic acid and nitric acid production (Kattenberg).
Other gases not mentioned above that have a small impact on the Green House Gas
proposed problem, is CFC-11 and CFC-12, these Gases are know to the public as being a
big source of warming, although catalyzing decomposition of stratospheric ozone, they
do not pose a great threat. Since the public was notified of these compounds in
refrigerants, spray propellants, and foam blowing; the atmospheric concentrations have
decreased greatly (Prather).
The danger that all these Green House Gases put to the atmosphere is the increase
in the infrared energy absorbed by the atmosphere. This extra energy absorbed although
thought to only warm the earth also has a cooling tendency on the stratosphere (Peixoto
and Oort). The affect the radiation has by this increase of Green House Gases
concentration is also known as Infrared Flux at the tropopause (Wang). The models
used to predict this information can also closely mimic the other layers of the atmosphere
as well as the surface. Worldwide temperature measurements are carefully taken with
many variables in mind. Such variables would be urbanization of a region, aerosols,
precipitation, and changes in temperature and clouds (Hansen). Usually the temperature is
the first variable that is considered when assessments of the world climate change are
taken, it is also very important to consider other data that is part of the climate system
along the line of time and space. Some other sources of information are: tree rings, bore
hole temperature measurements in the soil, permafrost, and ice sheets, and measurements
of the mass of valley glaciers and ice caps. By looking at this material for the past 600
years it has been determined that the warming in the twentieth century is greater over this
time period (Briffa).
From paleoclimate studies it has been concluded that the Earth’s climate has been
altered by more than just Green House Gases, but Inorder to find the effects of the Green
House Gases specifically, a study of records from the periods when the changes in the
atmospheric carbon dioxide were much larger than those of our century. Large natural
variation in the atmosphere’s carbon dioxide were found in the observation and analysis of
gas bubbles trapped in glacier ice cores, are correlated with glacial (ice age) and
interglacial climate change of the latest Pleistocene and Holocene epochs. These glacial
periods are associated with low carbon dioxide concentrations, and the interglacial periods
with high concentrations. When looking at methane concentrations within these cores,
there was a similar correlation (Chappellaz).
Some of the predicted changes to the Earth’s climate due to this continual rise in
Green House Gases are: increase in mean surface air temperature, increase in global mean
rates of precipitation and evaporation, rising of sea levels. An increase in the surface air
temperature would cause rates of evaporation to increase, causing the water vapor in the
air to rise. The positive feedback to the surface temperature increase is that is will lead to
a more intense hydrological cycle, with more precipitation events (Kattenberg). Another
possible consequence of greenhouse gas induced climate change is elevated sea levels.
The main cause for sea level fluctuation is due to thermal expansion and the melting of
glaciers, both are responses to higher air temperatures. Measurements taken from 93′ to
98′ indicate a melt rate from Greenland’s ice sheet of 1 meter a year (Krabill). There have
been measurements of the sea levels also, they indicate a rise of about 10 – 25 cm a year
All of these predictions were made by constructing models that help scientist
predict the climate change if the Green House Gases continue to rise at a steady rate.
Although scientist are fairly confident in these models there is room for error in these
models. Despite the gains there are a number of features of the climate system that are
still crudely represented in climate models. The models are restricted in their ability to
accurately represent terrain effects and to simulate processes that occur on a smaller scale.
Other shortcomings in the climate models is their inability to actually portray the effects of
aerosols, precipitation, and clouds and changes in solar irradiance. For these and other
reasons there remains scientific uncertainties in model predictions, including uncertainties
in the predictions of local effects of climate change, occurrence of extreme weather
events, effects of aerosols, changes in clouds, shifts in precipitation, and even changes in
ocean circulation (Hansen).
Aerosols are a big concern for model analysts, because aerosols are a principle
source of uncertainty in modeling climate changes during the industrial period. Aerosols
scatter and absorb short wave (solar) radiation and modify the reflectivity of clouds. Both
effects are thought to decrease the abortion of short wave radiation by the Earth, cooling
the climate, even though the troposphere aerosols only last a day in the atmosphere
Green House Gases are related to the warming of the Earth, but the future of the
climate is not yet know, or predicted. So many variables make up the atmosphere and it’s
climate, no model can accurately predict the future. Natural Earth warmers like water
vapor and clouds also contribute to the warming trend. The Earth’s records of ice ages
and tree rings can only paint a very small piece of this huge picture. scientist are at a
disadvantage because they are not able to see the Earth’s full past, as an instructor of mine
once said- they cannot predict the future of climate patterns when they have only been
studding the atmosphere for the last 100 years.