Chapter 6.2- The greenhouse effect and global warming
The Greenhouse effect
This is a natural process that occurs all the time and keeps average global temperatures at around
17°C. Without it, the average temperature on earth would be about -18°C. The greenhouse effect is
the result of the heat and light from the sun that reaches the earth. Some of this solar radiation is
reflected back into space, some is absorbed by the atmosphere, and fortunately, some reaches the
earth’s surface. Some of the radiation that reaches the earth’s surface is reflected back as heat and
is lost into space. Some is radiated back to earth by clouds and the greenhouse gases that form part
of the atmosphere. These gases trap this heat close to the surface of the earth, which keeps the
planet warm. The greenhouse gases act like the glass in a greenhouse, trapping heat beneath them.
Greenhouse gases
The most important greenhouse gas is carbon dioxide, partly because there is so much of it and
partly because it remains in the atmosphere a lot longer than other greenhouse gases (100 years,
compared with only 10 years for methane). It has been estimated that around 50-70% of global
warming is due to the carbon dioxide in the atmosphere. It is mainly the result of human activities
that the concentration of carbon dioxide is increasing, which is enhancing the greenhouse effect and
causing concerns for the environment. Another natural greenhouse gas is methane. Methane is
produced when microorganisms break down the organic molecules that comprise living organisms.
The majority of this occurs in one of two ways:
When decomposers break down the remains of dead organisms
When microorganisms in the intestines of primary consumers, such as cattle, digest the food
that has been eaten
Global warming
Since 1900, the average global temperature has increased by approximately 0.6°C, a change known
as global warming. The earth has always had periodic fluctuations in temperature. Therefore it
cannot be assumed that this increase in temperature is solely due to human activities, such as the
burning of fossil fuels and deforestation, which generate additional carbon dioxide. However, we can
say that the concentration of carbon dioxide has risen from 220ppm before the industrial revolution
to 370ppm today. We also know that carbon dioxide is a greenhouse gas. Most scientists think that
these human activities have contributed to global warming.
Consequences of global warming
Even if humans continue to release greenhouse gases at the present rate, it is by no means certain
what the effects would be. CO₂ levels may even be reduced naturally, as phytoplankton and other
plants increase their rates of photosynthesis.
It is expected that global warming will cause changes in temperature and levels of precipitation, as
well as affecting the timing of the seasons and the frequency of extreme weather events such as
storms, floods and droughts. Climate change will affect the niches that are available in a community.
The distribution of species will alter as each organism adapts to a new niche. If the rate of climate
change is slow, it is possible that species will have time to migrate to new areas where they will
begin to compete for the available niches. This may lead to the loss of native species that already
occupy the existing niches. It can be noted that many species are moving in the same direction as
the climate. For example, in the northern hemisphere, many species of butterflies, lichen and birds
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The Greenhouse effect
This is a natural process that occurs all the time and keeps average global temperatures at around
17°C. Without it, the average temperature on earth would be about -18°C. The greenhouse effect is
the result of the heat and light from the sun that reaches the earth. Some of this solar radiation is
reflected back into space, some is absorbed by the atmosphere, and fortunately, some reaches the
earth’s surface. Some of the radiation that reaches the earth’s surface is reflected back as heat and
is lost into space. Some is radiated back to earth by clouds and the greenhouse gases that form part
of the atmosphere. These gases trap this heat close to the surface of the earth, which keeps the
planet warm. The greenhouse gases act like the glass in a greenhouse, trapping heat beneath them.
Greenhouse gases
The most important greenhouse gas is carbon dioxide, partly because there is so much of it and
partly because it remains in the atmosphere a lot longer than other greenhouse gases (100 years,
compared with only 10 years for methane). It has been estimated that around 50-70% of global
warming is due to the carbon dioxide in the atmosphere. It is mainly the result of human activities
that the concentration of carbon dioxide is increasing, which is enhancing the greenhouse effect and
causing concerns for the environment. Another natural greenhouse gas is methane. Methane is
produced when microorganisms break down the organic molecules that comprise living organisms.
The majority of this occurs in one of two ways:
When decomposers break down the remains of dead organisms
When microorganisms in the intestines of primary consumers, such as cattle, digest the food
that has been eaten
Global warming
Since 1900, the average global temperature has increased by approximately 0.6°C, a change known
as global warming. The earth has always had periodic fluctuations in temperature. Therefore it
cannot be assumed that this increase in temperature is solely due to human activities, such as the
burning of fossil fuels and deforestation, which generate additional carbon dioxide. However, we can
say that the concentration of carbon dioxide has risen from 220ppm before the industrial revolution
to 370ppm today. We also know that carbon dioxide is a greenhouse gas. Most scientists think that
these human activities have contributed to global warming.
Consequences of global warming
Even if humans continue to release greenhouse gases at the present rate, it is by no means certain
what the effects would be. CO₂ levels may even be reduced naturally, as phytoplankton and other
plants increase their rates of photosynthesis.
It is expected that global warming will cause changes in temperature and levels of precipitation, as
well as affecting the timing of the seasons and the frequency of extreme weather events such as
storms, floods and droughts. Climate change will affect the niches that are available in a community.
The distribution of species will alter as each organism adapts to a new niche. If the rate of climate
change is slow, it is possible that species will have time to migrate to new areas where they will
begin to compete for the available niches. This may lead to the loss of native species that already
occupy the existing niches. It can be noted that many species are moving in the same direction as
the climate. For example, in the northern hemisphere, many species of butterflies, lichen and birds
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