Zusammenfassung der Ressource
Global warming
- Greenhouse gases
- Some gases in the Earth’s atmosphere absorb infrared radiation. One of
these is carbon dioxide. Even though carbon dioxide is only about 0.04 per
cent of the atmosphere, it is a very important greenhouse gas because it
absorbs infrared well.
- The Sun’s rays enter the Earth’s atmosphere
- Heat is emitted back from the Earth’s surface at a lower principal
frequency than that emitted by the Sun
- Some heat passes back out into space
- But some heat is absorbed by carbon dioxide, a greenhouse gas, and becomes
trapped within the Earth’s atmosphere. The Earth becomes hotter as a result
- Water vapour and methane
- Other greenhouse gases are water vapour, and also
methane. Even though methane is present in trace (tiny)
amounts only, it is a very efficient absorber of infrared.
- The carbon cycle
- The amount of carbon
dioxide in the atmosphere is
controlled by the carbon
cycle.
- Processes that remove carbon
dioxide from the air:
- photosynthesis by plants
- dissolving in the oceans.
- Processes that return carbon
dioxide from the air:
- respiration by plants, animals and microbes
- combustion ie burning wood
and fossil fuels such as coal,
oil and gas
- thermal decomposition of limestone, for
example, in the manufacture of iron, steel and
cement.
- Cellulose
- All cells contain carbon, because they all contain
proteins, fats and carbohydrates. For example, plant
cell walls are made of cellulose, a carbohydrate.
- Decomposers
- Decomposers, such as microbes and fungi, play an
important role in the carbon cycle. They break down the
remains of dead plants and animals and, in doing so,
release carbon dioxide through respiration.
- For thousands of years, the processes in the carbon cycle
were constant, so the percentage of carbon dioxide in the
atmosphere did not change. Over the past 200 years, the
percentage of carbon dioxide in the atmosphere has
increased steadily because humans are:
- burning more and more
fossil fuels as energy
sources
- burning large areas of forests to clear land,
which means that there is less
photosynthesis removing carbon dioxide from
the air.
- Global warming
- Although the changes have been gradual,
most - but not all - scientists agree that the
climate is getting gradually warmer. This is
called global warming.
- Most - but not all - scientists lay the blame for this on
human activities increasing the amount of carbon dioxide
in the atmosphere.
- Global warming could cause:
- climate change
- extreme
weather
conditions in
some areas.
- Climate change may make it impossible to grow certain food crops in some regions. Melting polar ice, and the
thermal expansion of sea water, could cause rising sea levels and the flooding of low-lying land. Extreme weather
events become more likely due to increased convection accompanied by more water vapour being present in the
hotter atmosphere.
- Computer climate models - Higher tier
- One piece of evidence that supports the view of scientists who
blame human activities for global warming has been provided
by 'supercomputers'. Computer generated climate models,
based on different amounts of carbon dioxide in the
atmosphere, produce the same changes as have been
observed in the real world.