Climate Change: 4 Lectures The Science - Today –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

Increase in Ambient Air Temperatures Increase in Sea-surface Temperatures Decrease in Ocean CO 2 Uptake Increase in Atmospheric CO 2 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: Climate Feedbacks

Historical Records and Evidence for Climate Change

Direct and Indirect Greenhouse Gases and Aerosols

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 A. Neftel et al, Historical CO2 Record from the Siple Station Ice Core, Physics Institute, University of Bern, Switzerland, Sept Atmospheric carbon dioxide (CO 2 ) concentrations (1750 to present)

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 M.A.K. Khalil, R.A. Rasmussen, and F. Moraes. Journal of Geophysical Research 98:14,753-14, Atmospheric methane (CH 4 ) concentrations

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 CO 2 (heat-absorbing ability) –the decay rate of each gas relative to that of CO 2 (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 CO 2 equivalents Climate Change 2001: The Scientific Basis. Summary for Policymakers; IPCC 2001

Greenhouse gas warming 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 sulfates (primary precursor - SO 2 ) 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 O 3 and their effects on the lifetime of CH 4 –CO t ~ 60 days so it competes for hydroxyl radicals --> affects abundance and lifetime of CH 4 –E.g. calculations indicate that 100 metric tons of CO emissions is equivalent to ~ 5 metric tons of CH 4 emissions oxidation --> O 3 formation –Nitrogen oxides, including NO and NO 2 promote O 3 formation impact (negatively) methane and HFC concentrations in the atmosphere. deposition of nitrogen oxides - “fertilizing the biosphere” --> may reduce atmospheric CO 2 (ecosystem N-limited) --> may increase atmospheric CO 2 (ecosystem N-saturated or poorly buffered) –Volatile organic compounds (VOCs) have some short-lived direct radiative-forcing properties promote O 3 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 0.6 o C.  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 CO 2 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 CO 2 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 SF 6 SF 6 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 used in gas-insulated substations, circuit breakers, and other electrical switchgear SF 6 is emitted into the atmosphere during equipment operation, maintenance, and SF 6 recycling activities fugitive emissions of SF 6 can escape from gas-insulated substations and switchgear through seals, especially from older equipment, during equipment installation and when equipment is opened for servicing SF 6 is a powerful greenhouse gas GWP: 23,900 times higher than CO 2 atmospheric lifetime: 3,200 years SF 6 Emissions Reduction Partnership for Electric Power Systems Annual Report, 2000