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Lecture 14

 

Acid Rain – Summary

•         Release of SO2 and NOx due to burning of hydrocarbons ΰ Potential of removal before burning (S) or by scrubbing after burning

•         Local problem was converted into regional problem by increasing height of smoke stakes

•         Most severe in areas with low buffering capacity ΰ hard rock areas

•         Direct consequences on organisms in surface waters

•         Long-term effects on forests due to changes in soil acidity and mobilization of toxic elements (ΰ Al) and removal of nutrients (ΰCa)

•         Areas most affected generally at distances > 500 km from ‘polluters’

•         Clean Air act and similar activities have had a recognizable impact on the release of gases leading to acid rain (Fig. 1)

 

CO2 and Global Warming

•         What we know for sure:

–        Release of CO2 (and other gases) from fossil fuel use

–        Increase of ‘greenhouse gases’ in the atmosphere

•         What we think we know:

–        Temperature increase

–        Changing weather patterns

–        Melting of ice (glaciers; sea ice)

•         What we guess will happen

–        Future scenarios:

•         Changing precipitation pattern

•         Sea level rise

•         Changes in ocean currents and wind patterns

 

Rise in CO2 levels

•         Observation: CO2 concentration has increased from 315 to 380 ppmv (Fig. 2)

•         Increase follows the same trend in southern and northern Hemisphere

•         Cyclicity observed in the record

–        Larger amplitude in the northern hemisphere

–        Influence of biosphere

 

•         Current rise of CO2 levels observed from 315 ΰ 380 ppm

•         CO2 levels in the past 20 Myrs have not reached values above 300 ppm (Fig. 3)

•         CO2 levels in the distant past were much higher

•         Only about 50 % of CO2 released from fossil fuels burning remains in the atmosphere (Fig. 4)

•         Ocean takes up ~ 50% of CO2

•         Role of biosphere not completely clear

•         Deforestation increases CO2 levels

•         Reforestation decreases CO2 levels

•         Changes in permafrost area could also play a role

 

Radiation budget at the surface of the earth

•         Spectrum of radiating body depends on temperature (Fig. 5):

–        Sun (~ 6000oK) ΰ spectrum in visible range (short-wave length radiation)

–        Earth (~ 300oK) ΰ outgoing radiation in infrared range (long-wave length radiation)

•         Atmospheric gases have specific absorption wave length

–        CO2 and other ‘greenhouse gases’ absorb infrared radiation

–        Ozone absorbs ultraviolet radiation (shielding function)

 

Consequences

•         Natural State: Greenhouse gases prevent long-wave length radiation from leaving the earth ΰ re-radiation and moderation of temperature extremes

•         Addition of Greenhouse gases: more radiation is kept from leaving ΰ Global Warming

 

Other Greenhouse Gases

•         Methane (Fig. 6)

•         Natural:

•         ‘Swamp-gas’

•         Natural gas seeps

•         Anthropogenic:

•         Rice paddies

•         Ruminants (beef; sheep etc.)

•         Landfills

•         By product of oil and gas production

•         A number of other gases also contribute to the greenhouse effect ΰ methane; N2O etc.

•         CO2 is dominant greenhouse gas (Fig. 7)

 

Consequences – do we see changes?

•         Observations (Fig. 8)

–        Temperature increase

–        Sea level rise

–        Melting of ice

•         Arctic sea ice

•         Glaciers

•         Antarctica