Transcript Chemistry: A World of Choices

Global Climate Change
Question of the Day
• Based on energy balance models, we would
expect the average surface temperature of the
earth to be only –18oC. However the temperature
is actually about 15oC.
Hmm…what
gives?
The Greenhouse Effect
• Solar radiation reaches the Earth’s surface as UV
and visible light
• Some is absorbed by the surface
• Some of this is then re-radiated as IR
• But some of the IR can’t get back out of the
atmosphere, and is reflected back to the earth
• So the earth’s temperature is higher than you
would otherwise expect – and we can live here!
The Earth’s Energy Balance
Greenhouse
effect
Our atmospheric
gases trap and
return a major
portion of the
heat radiating
from the Earth.
It is a natural,
necessary
process.
Web-based Animations of the Greenhouse Effect
http://www.planetguide.net/book/chapter_3/greenhouse_effect.html
Molecules: How They Shape Up
• Molecular shape will affect whether a molecule is a
‘greenhouse gas’ (GHG)
• Shape can be determined using Lewis Structures or
molecular models
• Reminder: The most stable molecular shape is the
one in which the bonding or nonbonding electron
groups attached to any atom are as far from each
other as possible
– Example: Water
CO2 and CH4 Molecules
The two most important greenhouse gases!
Molecular response to different types of radiation
Ozone
Greenhouse
effect
Cooking
Molecular Vibrations of CO2
Trends in Global Temperature
ISAT 112
1995
1997
1998
Average global surface temperatures have increased since
1880.
The red bars indicate average temperatures for the year while
the black error bars show the range for each year. The blue line
is the 5-year moving average.
Temperature Trends
More Temperature Trends…
Weihenstephen Brewery in Freising starts, 1040!
Temperature Trends in U.S.
Comparison of Greenhouse
Gases
•
•
•
•
•
Gas
Factor
Abundance% Impact
CO2
CH4
N2O
O3
CCl2F2
1
30
160
2000
25,000
3.7*10-2
1.8*10-4
3.1*10-5
4.0*10-6
5.2*10-8
1
.145
.132
.22
.035
These gases have the ability to capture outgoing IR radiation from the
earth, absorb that radiation, and re-radiate it back to the earth. The
greenhouse effect!
2010: 392.9 ppm
CO2 Measurements - Hawaii
2005: 379.5 ppm
http://www.esrl.noaa.gov/gmd/ccgg/trends/
Collecting glacial ice cores
The concentration of carbon dioxide (blue) and the global
temperature (red) are well correlated over the past 400,000
years as derived from ice core data.
The Vostok ice core goes back 400,000 years. The current
concentration of atmospheric carbon dioxide is 100 ppm
higher than any time in the last million years.
The carbon cycle
Carbon Reservoirs
Reservoir
Size (Gt of Carbon)
•Atmosphere
750
•Forests
610
•Soils
1,580
•Surface Ocean
1,020
•Deep Ocean
38,100
•Fossil Fuels
–Coal
4,000
–Oil
500
–Natural Gas
500
Total, all sources
47,060
Causes of GG increase
• Increased combustion
– Industrial revolution
– Fossil fuels
• Deforestation
– Amazon rainforest = 4,224,905 football fields/yr
8 football fields/minute
• Agriculture
• Melting of permafrost
CO2 Emissions by Country:
Total emissions since 1950 (b tons)
Graphic from: Michael Glantz, “What Makes Good Climates Go Bad? … and … “Why Care?” USAEE/IAEE Meeting, 9-19-05.
What might be true:
•
CO2 and other gases generated by human activity
contribute to the temperature increase.
In a recent poll, 97% of climate scientists believe that
this is true.
(http://www.sciencedaily.com/releases/2009/01/090119210532.htm)
•
The average global temperature will continue to rise
as emissions of anthropogenic greenhouse gases
increase.
Projected future
regional
patterns of
warming based
on three
emissions
scenarios (low,
medium, and
high growth).
Source: NASA
Earth
Observatory,
based on IPCC
Fourth
Assessment
Report (2007)
Temperature projections to the year 2100, based on a range of
emission scenarios and global climate models.
Global Climate Change bottom line
• There is ample evidence that
– the Earth experiences (and we rely on) the “greenhouse
effect”
– carbon dioxide is a “greenhouse gas”
– the temperature of the atmosphere has been rising over
the past century
– the concentration of carbon dioxide is also rising, and
correlates both to this increase in temperature and the
use of fossil fuels
• What is debated is whether humans are causing these
changes
• The Intergovernmental Panel on Climate Change (IPCC)
has said yes for years, and the Kyoto Protocol was intended
to address this
Sources of CO2
Fig. 3.17
Fig. 3.23
Fig. 3.23a
Fig. 3.23b
One Gallon Gas = 20 lbs CO2
• Is this right? What do we need to know to prove
it?
– What is the basic formula for gasoline?
– What is its density?
– How much carbon is in the gasoline?
– What are the products of its combustion?
– What is the ratio of CO2 produced to carbon
burned?
Analysis
•
•
•
•
•
8 pints/gal * 0.8 lb gas /pint = 6.4 lbs gas/gal
C8H18 = 114 g/mol, 84.21% C
6.4 lb gas/gal * 1000 g/2.2lbs = 2910 g gas
2910 g gas * .8421% C = 2450 g C
2450 g C/gal * 44 g/mol CO2/12 g/mol C = 8983
g CO2/gal
• 8983g CO2 * 2.2lb./1000g = 19.76 lb CO2/gal
gas
Carbon Cycle
Fig. p.115
Some Questions about Global
Warming
• Does increased CO2 in the atmosphere really
induce growth?
• Can forests and soils sequester enough carbon to
offset anthropogenic sources?
• How much proof is needed to recognize and act
on a problem like global warming?
• What should we/can we do at the individual
level?