Carbon dioxide and water vapor are the most significant greenhouse gases, responsible for 50% and 25% of the greenhouse effect respectively. Other gases like methane and nitrous oxide have smaller impacts, together accounting for less than 10%. The impact of a gas depends on how strongly it absorbs infrared radiation and its concentration in the atmosphere. Rising levels of carbon dioxide and other greenhouse gases since the industrial revolution have caused increased warming of the Earth's surface and atmosphere by trapping more of the infrared radiation emitted by the Earth. Multiple independent scientific analyses of ice core and other data show that increases in atmospheric carbon dioxide correspond to increases in global temperature.

1. Topic 4.4 Climate Change
IB Biology
R. Price
v. 1 2015

2. Allott 229

3. #1: Carbon dioxide and water vapour are the most significant
greenhouse gases
Carbon Dioxide
• Into atmosphere -> cell respiration,
combustion biomass, fossil fuels
• Removed from atmosphere -> dissolve
in oceans, photosynthesis
Water Vapour
• Into atmosphere -> evaporation from
ocean, transpiration from plants
• Removed from atmosphere -> rain &
snow

4. #2: Other gases including methane and nitrogen oxides have less impact
Greenhouse Effect
•Water vapor = 50%
•Clouds = 25%,
•Carbon dioxide (CO2)= 20%
•Methane (CH4) = 5%
•Nitrous oxide (N2O) = < 1%
Oxygen & nitrogen NOT greenhouse
gases (don’t absorb longer-wave
radiation) By Andrew Lacis [Public domain], via Wikimedia Commons

5. #3: The impact of a gas depends on its ability to absorb long-wave
radiation as well as on its concentration in the atmosphere
Warming impact of greenhouse
gas:
1. How readily absorbs long-
wave radiation
2. Concentration of the gas in the
atmosphere
Methane absorbs more
radiation than carbon dioxide,
but there’s more carbon
dioxide in the atmosphere

6. #4: The warmed Earth emits longer-wave radiation (heat)
• Surface of the Earth absorbs
short-wave radiation from the
sun
• Earth re-emits energy as longer-
wave radiation

7. #5: Longer-wave radiation is reabsorbed by greenhouse gases which
retains the heat in the atmosphere
• Ozone (O3) in atmosphere absorbs
25-30% short wavelength radiation
(UV) before it reaches the Earth
• Earth re-emits energy as longer-
wavelength radiation (heat)
• 70-80% of re-emitted energy
captured by greenhouse gases
If we didn’t have global warming,
Earth’s surface = -18 deg. C

8. #6: Global temperatures and climate patterns are influenced by
concentrations of greenhouse gases
Ice Cores from Antarctic
•Remember, correlation does not
prove causation
•Evidence supporting hypothesis
•CO2 is a greenhouse gas
•Ice cores have bubbles of trapped
gas
•Measure CO2 in trapped bubbles
• Measure hydrogen isotope ratios in
ice for temperature
•As CO2 levels rise, so do global
temperature

9. Allott 233

10. Allott 234

11. #7: There is a correlation between rising atmospheric concentrations of
carbon dioxide since the start of the industrial revolution two hundred
years ago and average global temperatures
• Large fluctuations in CO2 over
last 800,000 years. But. . .
• CO2 levels have never been this
high (400 ppm)
• Unnatural rise since 1950
• Combustion of coal, oil, natural
gas
• Correlation between rising
atmospheric CO2 levels and
global temperature

12. #8: Recent increases in atmospheric carbon dioxide are largely due to
increases in the combustion of fossilized organic matter
•Since 1950, large
increases in global
combustion of fossil
fuels
•Coal, oil, natural gas
used for power
generation &
transportation

13. Allott 236

14. Allott 236

15. Allott 237

16. Allott 237

17. Allott 238

18. Sources
Content
Allott, Andrew, and David Mindorff. Biology: Course Companion. 2014
ed. Oxford: Oxford UP, 2014. Print. Oxford IB Diploma Programme.
Walpole, Brenda. Biology for the IB Diploma. 2nd ed. Cambridge:
Cambridge UP, 2014. Print.
Images
Unless otherwise noted, images are obtained from Pixabay
(www.pixabay.com) and used under the CC0 Public Domain license.