Download the_science - The Global Change Program at the University of

Climate Change: 4 Lectures
• The Science - Today
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The climate system
Historical records and evidence of climate change
Direct and indirect greenhouse gases and aerosols
Key findings 2001
• Emissions Scenarios - 3/22
– Climate Models
– Uncertainties
• Potential Impacts and Mitigation Strategies - 3/25
• Case Studies: China & United States of America - 3/27
The Climate System
Schematic view of the components of the global climate system (bold),
their processes and interactions (thin arrows) and some aspects that may
change (bold arrows).
Climate Change 2001: The Scientific Basis; IPCC 2001
Distribution of heat and water occurs because of vertical convection
currents that stir up air in the troposphere and transport heat and water
from one area to another in circular, convection cells.
Global air circulation and biomes
The direction of air flow and the ascent and descent of air masses in
these convective cells determine Earth’s general climatic zones.
NRC, Improving the Effectiveness of U.S. Climate Modeling, 2001
Climate Feedbacks
Feedbacks in the climate system occur when the output from
one component is input into a second component, which then
generates an output altering the first component.
Example:
Increase in
Ambient Air Temperatures
Increase in
Sea-surface Temperatures
Increase in
Atmospheric CO2
Decrease in
Ocean CO2 Uptake
Historical Records and
Evidence for
Climate Change
Direct and Indirect
Greenhouse Gases
and
Aerosols
Atmospheric carbon dioxide (CO2)
concentrations (1750 to present)
Data Source: C.D. Keeling and T.P. Whorf, Atmospheric CO2 Concentrations (ppmv) derived from in
situ air samples collected at Mauna Loa Observatory, Hawaii, Scripps Institute of Oceanography,
August 1998. A. Neftel et al, Historical CO2 Record from the Siple Station Ice Core, Physics
Institute, University of Bern, Switzerland, Sept. 1994.
Atmospheric methane (CH4) concentrations
Data Source: D.M. Etheridge et al. Concentrations of CH4 from the Law Dome (East Side, "DE08"
Site) Ice Core(a), Commonwealth Scientific and Industrial Research Organisation, Aspendale,
Victoria, Australia. September 1994. http://cdiac.esd.ornl.gov/ftp/trends/methane/lawdome.259.
M.A.K. Khalil, R.A. Rasmussen, and F. Moraes. Journal of Geophysical Research 98:14,753-14,770.
1993. http://cdiac.esd.ornl.gov/ftp/db1007/cmeares.mon
Global warming potentials (GWPs)
• used to compare the abilities of different greenhouse gases to trap
heat in the atmosphere
• based on
– the radiative efficiency of each gas relative to that of CO2
• (heat-absorbing ability)
– the decay rate of each gas relative to that of CO2
• (the amount removed from the atmosphere over a given number of years)
• provides a construct for converting emissions of various gases into
a common measure
– allows climate analysts to aggregate the radiative impacts of various
greenhouse gases into a uniform measure denominated in carbon or
CO2 equivalents
Climate Change 2001: The Scientific Basis. Summary for Policymakers; IPCC 2001
Greenhouse gas warming
Other
Halocarbons
5%
CFC-12
6%
Carbon
Dioxide
64%
Nitrous Oxide
6%
Methane
19%
Source: J. T. Houghton et al., eds. Climate Change 1995: The Science of Climate Change,
published for the IPCC, in collaboration with WMO and UNEP
Aerosols
– small airborne particles or droplets
– most prominent
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sulfates (primary precursor - SO2)
fossil fuel black carbon (“black soot”)
fossil fuel organic carbon aerosols
biomass-burning aerosols
– direct effects
• absorb and scatter solar and thermal radiation
– sulfates, -0.4 watts m-2; black soot, +0.2 watts m-2
– fossil fuel organic carbon, -0.1 watts m-2; biomass-burning aerosols, -0.2 watts m-2
– indirect effects
• modify the physical properties and amount of clouds
– climate effects uncertain
– preliminary evidence points to an indirect cooling effect due to cloud formation
Climate Change 2001: The Scientific Basis. Summary for Policymakers; IPCC 2001
Indirect greenhouse gases
• influence climate indirectly through the formation of O3 and their
effects on the lifetime of CH4
– CO
• t ~ 60 days so it competes for hydroxyl radicals --> affects abundance and
lifetime of CH4
– E.g. calculations indicate that 100 metric tons of CO emissions is equivalent to ~ 5
metric tons of CH4 emissions
• oxidation --> O3 formation
– Nitrogen oxides, including NO and NO2
• promote O3 formation
• impact (negatively) methane and HFC concentrations in the atmosphere.
• deposition of nitrogen oxides - “fertilizing the biosphere”
--> may reduce atmospheric CO2 (ecosystem N-limited)
--> may increase atmospheric CO2 (ecosystem N-saturated or poorly buffered)
– Volatile organic compounds (VOCs)
• have some short-lived direct radiative-forcing properties
• promote O3 formation
• promote organic aerosol production
Climate Change 2001: The Scientific Basis. Summary for Policymakers; IPCC 2001
Key Findings
Third Assessment Report
Intergovernmental Panel
on Climate Change
(IPCC 2001)
Key findings, Third Assessment Report
International Panel on Climate Change
 The global average surface temperature has increased over the
20th century by about 0.6oC.
 Temperatures have risen during the past four decades in the lowest
8 kilometers of the atmosphere.
 Snow cover and ice extent have decreased.
 Global average sea level has risen and ocean heat content has
increased.
 Concentrations of atmospheric greenhouse gases and their
radiative forcing have continued to increase as a result of human
activities.
Climate Change 2001: The Scientific Basis. Summary for Policymakers; IPCC 2001
Key findings, Third Assessment Report
International Panel on Climate Change, cont’d.
 Natural factors have made small contributions to radiative forcing
over the past century.
 There is new and stronger evidence that most of the warming
observed over the past 50 years is attributable to human activities.
 Human influences will continue to change atmospheric composition
throughout the 21st century.
 Global average temperature and sea level are projected to rise
under all IPCC SRES scenarios.
 Anthropogenic climate change will persist for many centuries.
Climate Change 2001: The Scientific Basis. Summary for Policymakers; IPCC 2001
After CO2 emissions are reduced and atmospheric concentrations stabilize, surface air
temperature continues to rise slowly for a century or more. Thermal expansion of the ocean
continues long after CO2 emissions have been reduced, and melting of ice sheets continues to
contribute to sea-level rise for many centuries.
(This figure is a generic illustration for stabilization at any level between 450 and 1,000 ppm.)
Climate Change 2001: Synthesis Report; IPCC 2001
NEXT (3/22 ):
Emissions Scenarios
Climate Models
Uncertainties
Use and Climate Impact of SF6
SF6 is used for the safe transmission and distribution of electricity.
•
high dielectric strength, high VP, arc-quenching abilities, and lack of toxic or
corrosive effects make it an efficient and easy-to-handle electrical insulator
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used in gas-insulated substations, circuit breakers, and other electrical
switchgear
SF6 is emitted into the atmosphere during equipment operation,
maintenance, and SF6 recycling activities
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fugitive emissions of SF6 can escape from gas-insulated substations and
switchgear through seals, especially from older equipment, during
equipment installation and when equipment is opened for servicing
SF6 is a powerful greenhouse gas
• GWP: 23,900 times higher than CO2
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atmospheric lifetime: 3,200 years
SF6 Emissions Reduction Partnership for Electric Power Systems Annual Report, 2000