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Global Climate Change
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Our changing climate
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What is Climate Change? Climate = long-term weather patterns (what you expect; weather is what you get!) GCC = changes in long-term pattern of atmospheric conditions involving ∆T, precipitation, storm frequency & intensity Global warming is one aspect
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Greenhouse Effect Short-wave radiation absorbed by earth
Earth warms up, releases IR radiation Tropospheric greenhouse gases (CO2, CH4, H20) absorb IR
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Greenhouse Effect Due to abundance, CO2 is of primary concern
Current levels at their highest in 650,000 – 2,000,000 years Fossil fuel burning, forest clearing and burning are the two main anthropogenic sources of increased CO2 levels
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Greenhouse Gases Methane (from fossil fuel extraction, cattle, landfills, certain crops like rice) N2O from feedlots, automobiles, agriculture Tropospheric O3 Halocarbons have decreased due to Montreal Protocol of 1987 Aerosols may have short-term cooling effect
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Other Factors Milankovitch cycles = changes in the earth’s rotation and orbit around the sun Solar output and solar cycle Ocean absorption of CO2
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Other Factors El Niño = Equatorial winds weaken and allow warm water from western Pacific to move eastward Prevents cold water from upwelling in eastern Pacific La Niña = Cold surface waters extend far westward
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Other Factors Thermohaline circulation = worldwide current system in which warmer fresher water moves along the surface; colder, saltier water moves down North Atlantic Deep Water = warm surface water moves northward toward Europe; cooler water sinks and returns in other direction
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Studying climate change
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Proxy Indicators Preserved gas bubbles in ice
Sediment beds beneath bodies of water Coral reefs and tree rings All are forms of indirect evidence
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Atmospheric Sampling Started in 1958 – Charles Keeling of Scripps Institution of Oceanography – trends of CO2 concentrations His data showed shows an increase of CO2 concentrations from 315 to 383 ppm
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Modeling Coupled general circulation models (CGCMs)
Combine what is known about weather patterns, atmospheric circulation, atmosphere-ocean interactions, and feedback mechanisms to simulate climate processes Over a dozen research labs world wide A good approximation of relative effects of natural and anthropogenic influences
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Current & future impacts
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IPCC Report 2007 – summarized 1000s of reports
Includes trends in sfc temp, rainfall patterns, snow & ice cover, sea levels, storm intensity, etc Included a series of possible climate change scenarios, including: Temp increases (1.33oF in last century) Increases in power and duration of storms Changes in precipitation
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Muir Glacier: 1948 and Now
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IPCC Report Polar ice melt
Glaciers disappearing (Since 1980 – glaciers have lost an average of 9.6 m vertical This changes earth’s albedo Rising sea levels (3.1 mm/y from 1993 – 2003) A several inch vertical rise = many feet of horizontal incursion into coastal lands
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IPCC Report Storm surges present a great risk to island nations
Rising sea levels will force people to choose between relocating or investing in costly protections Ecosystems also affected Timing of seasonal events are creating complex effects in ecosystems
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IPCC Report Societal impacts will also occur
Agriculture – cuts in productivity (drought & flood) Forestry – insects, disease outbreaks, , invasive species, fires Health – heat stress, tropical diseases, respiratory ailments, hunger Economics – est. of 1 – 5% of GDP
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Responding to climate change
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Our Response Mitigation or adaptation?
Mitigation = actions that would reduce emissions of GHG Adaptation = search for ways to soften the blow (building sea walls is an ex.) Electricity generation is largest source of GHG in US Conservation & efficiency
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Our Response Natural gas has less impact
Carbon sequestration would allow current practices to continue Transportation is 2nd largest source Cars are highly inefficient (15%) Alternative engines, driving less, public transportation are possibilities
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Our Response Sustainable agriculture & land management
Reduce methane emissions from rice fields, cattle Preserving forests; increase reforestation Recovering methane from landfills, treating wastewater, energy from solid waste
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Our Response Kyoto Protocol
Began as the UN Framework Convention on Climate Change Binding international treaty to reduce GHG emissions (US refused to sign) In the 10 years after Rio conference (1992) – US increased GHG by 13%; Germany & UK decreased by 13 – 18%
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Our Response Market mechanics – cap and trade
A carbon offset represents a reduction in emissions somewhere else - like a renewable energy or a reforestation project - to balance out the emissions you cannot reduce. Reduce your own carbon footprint
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Ozone depletion
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UVA: λ = nm Causes tanning UVB: nm; burns, skin cancer UVC: nm formation of ozone
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Research CFCs are persistent in the atmosphere
Rise into the stratosphere over years Break down under high-energy UV radiation Halogens produced accelerate the breakdown of O3 to O2 Each CFC molecule can last years
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Reducing Effects Stop producing all ozone-depleting chemicals
60–100 years of recovery of the O3 layer 1987: Montreal Protocol; 1992: Copenhagen Protocol Ozone protocols: prevention is the key Substitutes for CFCs are available
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Conclusion Many factors, including human activities, can shape atmospheric composition and global climate. Scientists and policymakers are beginning to understand anthropogenic climate change and its environmental impacts more fully. Reducing greenhouse gas emissions and taking other actions to mitigate and adapt to climate change represents the foremost challenge for our society in the coming years.
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