Chapter 14: EnergyIB Option C

Part 5: Environmental impact: global warming(C.5) – pp. 823-829
C.5 – Gases in the atmosphere that are produced by human activities are changing the climate as they are upsetting the balance between radiation entering and leaving the atmosphere.
Greenhouse Effect: greenhouse gases allow the passage of incoming solar short-wavelength (visible and UV) radiation, but absorb the longer-wavelength (infrared/IR) radiation from the Earth. Some of the absorbed radiation is ______back to Earth.

Why? A covalent bond is like a spring in that it vibrates at a ______. When incoming IR radiation = natural frequency of bond, then molecule absorbs the radiation and the bond increases vibrational energy. This makes the air warmer, causing it to radiate heat in turn (some heat radiated to space and some back to earth).

This natural process is called ______because the Sun’s energy is absorbed in a way that is similar to the way light energy is trapped by the glass in a greenhouse. The glass lets light energy in but does not let heat out. This is necessary on some level for life as we know it on Earth.

The concern stems from the fact that human activities are increasing the concentrations of greenhouse gases at unprecedented rates, leading to ______occurring at an alarming rate. On your exams, avoid using pop-journalistic terms like “bounce off,” “trapped” or “reflected” when talking about the greenhouse effect.

Not all gases are equally effective at absorbing IR, as this depends on the change in ______that occurs as a molecule vibrates.

  • Symmetric non-polar diatomic molecules like N2 and O2 are not greenhouse gases as they do not absorb IR.
  • Thegreenhouse factor of a molecule compares ability of substance to absorb IR to CO2’s ability to do so.
  • 10 molecules of H2O = effect of ______CO2 molecule
  • 1 molecule of CH4 = effect of ______CO2 molecules

Table 5.1: Major greenhouse gases in order of abundance
Note: water’s contribution not considered since human activity does not directly affect water vapor concentrations except at the local level. Majority of the greenhouse effect comes from water vapor, but changes are short lived – 9 day residence time compared to years for other gases

Gas / Main Source / Heat Trapping Effectiveness Compared With CO2
(a.k.a. “Greenhouse factor”) / Relative abundance (%) / Overall contribution to increased global warming (%)
Evaporation of oceans / 0.1 / 0.10 / -
Combustion of fossil fuels and biomass / 1 / 0.036
Anaerobic decay of organic matter caused by intensive farming / 30 / 0.0017 / 18%
Artificial fertilizers and combustion of biomass / 160 / 0.0003 / 6%
Secondary pollutant in photochemical smog / 0.0003 / 12%
Refrigerants, propellants, foaming agents, solvents / 10,000-25,000 / <0.000001 / 14%

Figure 5.1(Left)Radiative Forcing. Source: Figure 2, FAQ 2.1, IPCC Fourth Assessment Report (2007), Chapter 2, Changes in Atmospheric Constituents and in Radiative Forcing.(Right)Atmospheric concentrations of important long-lived greenhouse gases over the last 2,000 years. Increases since about 1750 are attributed to human activities in the industrial era. Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion air molecules, respectively, in an atmospheric sample. (Data combined and simplified from Chapters 6 and 2 of 2007 IPCC report.)

Figure 5.2:(Left) Temperature changes over time. Source: NASA. Regular up and down of temp and CO2 data corresponds to seasonal plant growth in N. Hem.
(Right) Relationship between CO2 levels and temp. Source: NOAA, based on Vostok ice core data
Time sequence: NASA data
How do we know? (CO2 over time):

Effects of increasing amounts of greenhouse gases on the atmosphere:

  • Rising ______(from thermal expansion of oceans and melting of the polar ice-caps)
  • Changes in precipitation and temperature of regions (causing ______and droughts)
  • Changes in yield and distribution of commercial ______
  • Changes in distribution of ______and disease-carrying organisms

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Chapter 14: EnergyIB Option C

Heterogeneous equilibrium between atmospheric carbon dioxide and aqueous carbon dioxide in the oceans

About _____ of the CO2produced by combustion of fossil fuels is absorbed by plants during photosynthesis or dissolved by the oceans.

The CO2 reacts with water to from ______:

The ______then reacts to form hydrogencarbonates or carbonates:

  • This leads to higher ocean ______, mainly near the surface where the CO2 is absorbed.
  • This higher ______inhibits ______growth in marine animals and is suspected to be a cause of reproductive disorders in some fish.
  • Average pH levels have dropped from 8.2 to ______.
  • This drop of 0.1 represents a 25% increase in acidity, making it a serious cause for concern.

Global Dimming

  • ______can lower temperature by scattering light so that less radiation reaches Earth
  • These effects have been observed after major volcanic events in history.
  • Can also be caused by ______sources such as incomplete combustion of coal, oil and wood, which produces tiny airborne particles of ______, ______, sulfur compounds and other pollutants that reflect sunlight back into space.
  • Pollutants also serve as ______for the formation of water droplets.
  • Polluted clouds are more ______then unpolluted clouds because they contain more ______.
  • It is suggested that global dimming has limited the full effects of global ______.

Reducing carbon dioxide levels

Table 5.2: Strategies for reducing carbon dioxide levels

Strategy / Action
  • Use of insulation and more energy efficient appliances
  • Reducing personal energy use (turning off lights & electronics when not in use)
  • Reducing distance traveled in vehicles; use hybrid or electric cars or public transport

  • Use alternative sources such as solar, wind, geothermal, hydropower, wave or tidal power
  • Use reduced carbon fuels such as natural gas
  • The potential use of biomass depends on the processes by which it is converted to energy

  • CO2 can be removed from atmosphere and store within plant &soil, supporting the plants
  • Alternatively, CO2 can be captured either before or after fossil fuel is burned and then stored (sequestered) within the earth
  • Reduce deforestation and plant more trees

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