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Most of the dry atmosphere is made up of nitrogen (78.1%), oxygen
(20.9%) and argon (0.93%). Natural greenhouse gases make up less
than 1 % of atmosphere.
This diagram of the atmosphere above our Earth shows the greenhouse
- the troposphere.
This is the layer of our atmosphere - the layer closest to earth - the
troposphere - where natural greenhouse gases collect. These gases
act as insulation - i.e. increase the amount of heat that is trapped
here. This extra heat energy - which does not escape back into
the stratosphere, causes the temperature to increase and changes
the climate in the greenhouse.
The earth's temperature would be about 33oC less without this
natural greenhouse. In other words, the energy from the sun alone
would only keep the earth temperature at -19oC. Natural greenhouse
gases and water vapour keep at Earth's
surface at present global surface temperature of 14oC.
This means that the earth is 33oC warmer than it otherwise would
be without these natural greenhouse gases and water vapour. i.e.
from -19oC to +14oC = 33 degrees warmer. See Section 3.2.1 re:
The sun and global energy balance.
Source: Solar UV in our World (2002) ACER, Environment
Canada, Health Canada www.acer-acre.org
This means that the earth is 33oC warmer because of the natural
greenhouse gases and water vapour. See the pie graph below. Also
check Section 3.2.1 The sun and global energy balance.
ACTIVITY 1
Calculate
the relative thickness of each layer shown as a percentage of the
height of a door frame. Mark with labeled
tape. Add the ozone layer as a thin line at the tropopause!
They are called greenhouse gases because they provide an insulating
effect like a lowered ceiling in a room that reduces the amount
of heat the room needed to keep the room at a comfortable temperature.
Carbon dioxide is only 0.03 percent of our atmosphere but has
a much larger effect as the main insulation material responsible
for the Earth's greenhouse. Higher carbon dioxide CO 2 mean
thicker insulation and a greenhouse that requires less heat to
maintain the global surface temperature at 14oC. This also means
that the more CO 2 in our troposphere, the higher the
global temperature becomes if human activities, especially the
burning of fossil fuels, continue at the same rate.
Source: IPCC 1990. Climate Change: The IPCC Scientific Assessment [Houghton,J.T.
et al. (eds.)]. Cambridge University Press, Cambridge, UK. pg 48.
Climate models suggest that, if water vapour were the only greenhouse
gas present in the atmosphere, its magnitude would be only about
60-70% of that for all greenhouse gases.
If carbon dioxide were the only greenhouse gas present, the effect
would be about 25% of that of all gases.
ACTIVITY 2
- What is the present concentration of these gases in our atmosphere?
- Calculate how effective each of these gases is as an insulator.
The increased temperatures causing climate change are mainly due
to the increased concentration of carbon dioxide and other non-natural
greenhouse gases that human activities have added to the earth's
atmosphere. Human emissions are currently adding @28 tonnes CO2 per
year. Doubling concentration from 0.03% to 0.06% by end of this century
is predicted with possibility of tripling! Ratios of Carbon 12,13 and
14 are used to track this. See PRESENT 5.1.1a and FUTURE 6.1.1a
for more information re carbon dioxide concentrations in the atmosphere.
See Enhanced Greenhouse Gases 3.3.2a
The boundary or tropopause is easy to see above the earth's surface.
Note the thunderstorm in the troposphere and the clear stratosphere
above it. Find the thin blue line which indicates the ozone layer.
Science and Impacts of Climate Change CD -Presentation
Graphics (2002) MSC Environment Canada/ ESS Natural Resources Canada,
December
ACTIVITY 3
- Find the earth's size as a planet eg diameter in kilometers.
Measure the height of the troposphere in cm. Calculate the thickness
of the planet's greenhouse troposphere.
- 2. Translate to ratio
and proportions and use the CN as the earth and the troposphere
as a layer on in it e.g. the thickness of a
dime?
The troposphere contains very little ozone, which is toxic to
humans, plants and animals. However, the stratosphere, some 12
to 50 kilometers above the surface, contains significant amounts
of ozone that absorb all incoming UV-C and most UV-B radiation
from the sun. This protects surface ecosystems from this harmful
radiation, and is therefore also an important life-supporting role
of the atmosphere.
The article below helps to put everything together for easier
understanding.
Source: Solar UV in our World (2002) ACER, Environment
Canada, Health Canada www.acer-acre.org
Good planets are hard to find!
Source: IPCC 1990. Climate Change: The IPCC Scientific Assessment [Houghton,J.T.
et al. (eds.)]. Cambridge University Press, Cambridge, UK. pg.
Xxxvii Images: NASA
ACTIVITY 4
- Look at the surface temperatures of each of these planets,
the percentage of carbon dioxide in their atmosphere and finally
the number of Celsius degrees that the planet is warmer due to
the insulating ability of carbon dioxide.
- Using the information given for Earth, calculate the relationship
between 0.01% CO2 and surface temperature 0C. i.e. For every
0.01% increase in carbon dioxide, there could be an increase
in surface temperature of ______oC.
The high surface temperatures on Venus are partly due to being
closer to the sun. The main reason Venus is hotter is the strong
greenhouse effect induced by a dense atmosphere almost entirely
made up of carbon dioxide.
Mars is cold because it is farther from the sun than earth and
has a very thin atmosphere. Despite the high CO2 concentration,
the net greenhouse effect is much weaker than for earth. In 2004,
space expeditions proved that Mars had evidence of frozen water.
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