IB Biology – Topic 4. Human Impacts – Global Warming Fact Sheet
Greenhouse Effect
Greenhouse gases allow light to pass through to the earths surface, but
trap the longer wavelengths reflected from the earth. This keeps the
surface of the earth warmer than it would be without. Without this natural
effect in the atmosphere life would not survive on the earth. The moon
has no greenhouse and has an average temperature of around 17 degrees
lower than the earth.
Greenhouse Gases:
Gases and Source
Carbon Dioxide from any
combustion, decomposition or
respiration.
Methane from anaerobic respiration
and decomposition in rice fields
swamps. Landfill sites and flatulent
cows.
Nitrogen Oxides formed from
atmospheric nitrogen in the internal
combustion engines.
Chlorofluorocarbons (CFCs) from
fridge coolants and aerosol cans.
Significance
No. 1 cause of Global Warming
GW Potential 1, Atmospheric
concentration – 360ppm and
increasing rapidly
No. 2 cause of Global Warming
GW Potential 21, atmospheric
concentration - 1.72ppm – major
stores under arctic permafrost.
No. 3 cause, GW Potential = 206.
Atmospheric concentration= 0.31
Most potent greenhouse gas per
molecule GWP = 3500-7000 times
carbon dioxide, but due to low levels
less significant than the other gases.
Also depletes ozone in stratosphere
Climate Change: global warming (or the enhanced greenhouse effect)
Global average temperatures have increased significantly over the 20th
century, but the cause is not agreed on. Climate scientists use computer
models to predict that future average temperatures may increase by over 5oC
by the year 2100. This increase would have significant effects on health, food
production, water supply and ecosystems
Many people believe that an enhanced greenhouse effect is caused by
increases in carbon dioxide, methane and other greenhouse gases. The
increase in these gases is entirely human-made. The most significant
greenhouse gas is carbon dioxide, in terms of the actual warming it will
produce. The second most significant gas is methane although the gas
chlorofluorocarbon is the most powerful gas per molecule. It is also known
that climate can be affected by the earth’s orbit and the tilt of the axis. These
external factors may be more important in changing the temperature of the
earth, as many scientists argue.
Current levels of the greenhouse gases carbon dioxide and methane in the atmosphere are higher now than at any time in the past 650,000 years.
24 Nov 2005
650,000 years of greenhouse gas concentrations
The latest results from the EPICA core in Antarctica have just been published this week in Science (Siegenthaler et al. and Spahni
et al.). This ice core extended the record of Antarctic climate back to maybe 800,000 years, and the first 650,000 years of ice have
now been analysed for greenhouse gas concentrations saved in tiny bubbles. The records for CO2, CH4 and N2O both confirm the
Vostok records that have been available for a few years now, and extend them over another 4 glacial-interglacial cycles. This is a
landmark result and a strong testament to the almost heroic efforts in the field to bring back these samples from over 3km deep in
the Antarctica ice. So what do these new data tell us, and where might they lead?
First of all, the results demonstrate clearly that the relationship between climate and CO2 that had been deduced from the Vostok
core appears remarkably robust. This is despite a significant change in the patterns of glacial-interglacial changes prior to 400,000
years ago. The 'EPICA challenge' was laid down a few months ago for people working on carbon cycle models to predict whether
this would be the case, and mostly the predictions were right on the mark. (Who says climate predictions can't be verified?). It
should also go almost without saying that lingering doubts about the reproducibility of the ice core gas records should now be
completely dispelled. That a number of different labs, looking at ice from different locations, extracted with different methods all
give very similar answers, is a powerful indication that what they are measuring is real. Where there are problems (for instance in
N2O in very dusty ice), those problems are clearly found and that data discarded.
Problems Caused by Global Warming
Some of the effects include an increase in sea level, caused mostly by
thermal expansion, which threatens low lying lands such as the Maldives
and the Netherlands with flooding. Predictions of changes in climatic
hazards include an increase in the frequency and intensity of tropical
cyclones (hurricanes).
Diseases such as malaria are likely to spread as it gets hotter. Species
extinctions are likely to increase as the conditions change mainly because
of lack of suitable habitat. In a hotter, drier climate many regions of the
world will be unable to produce food or rely on water supplies in the
same way as before.
Global Warming
Control of greenhouse
gases –
Carbon Dioxide by
reducing fossil fuel
burning, stopping
deforestation and
planting more trees.
Methane by preventing
anaerobic
decomposition in wet
landfill sites. Sealed
landfill or recycling of
organic materials into
compost.
The Kyoto protocol
involves many countries
aiming to reduce the
amount of greenhouse
gases by around 5
percent of the 1990
emission level.
Many significant
countries such as the
USA have not agreed to
take part.
The effects of such a
small reduction are
unlikely to be very
significant.