Transcript Chapter 15 - Atmospheric Science Group

Chapter 15
Human Influences on
Climate
Figure CO: Chapter 15, Human Influences on Climate--Air pollution in
New York City
© Dean D. Fetterolf/ShutterStock, Inc.
Feedback: change leads to change
leads to more change
• Positive feedback mechanism: reinforces
(enhances) the original trend (change)
• Negative feedback mechanism: damps out an
existing trend (change)
• Example of a positive feedback mechanism:
warming, evaporation, water vapor,
warming
More climate feedback mechanisms
• Example of a negative feedback mechanism:
warming, evaporation, water vapor, cloud,
cooling
• Another positive feedback mechanism:
– Called the ice/albedo feedback mechanism
– Cooling, more ice, higher albedo, more cooling
– Warming, less ice, lower albedo, more warming
Figure 01: Ice Albedo Feedback
Air Pollution
• Air pollutants are aerosol particles (liquids and
solids) and gases that, in high concentrations,
seriously affect the lives of people and
animals, harm plants, or threaten ecosystems.
• Air pollutants can come from natural sources
(volcanoes, forest fires, dust storms) or human
activities (anthropogenic sources)
Figure 02: CO in lower troposphere – satellite image
Courtesy of NASA
Anthropogenic Sources of Air Pollution
• Transportation: motor vehicles, aircraft, ships
• Energy generation: electricity generation
• Industry: smelting, dry cleaning,
manufacturing
• Home heating
Carbon dioxide can be considered a pollutant
Primary Air Pollutants
• Emitted directly by sources
• Carbon monoxide, a gas, incomplete
combustion, can cause death in small
concentrations, emitted by vehicles and
defective heating devices
• Lead, a particulate, brain damage, in some
paints and treated gasoline, outlawed now
More Primary Air Pollutants
• Oxides of sulfur, sulfur dioxide and sulfur
trioxide, respiratory irritant, emitted in
burning fossil fuels containing sulfur
• Oxides of nitrogen, nitric oxide and nitrogen
dioxide, pulmonary problems, emitted by
high-temperature combustion of fossil fuels in
transportation and electric energy generation
More Primary Air Pollutants
• Hydrocarbons, also called volatile organic
compounds, or VOCs
– Some are carcinogens
– Are made up of hydrogen and carbon
– Emitted by motor vehicles, dry cleaning
• Particulates, small particles
– Smallest are most dangerous to lungs
Figure T01: Trends in Air Pollutant Concentrations in the United States from
1990 to 2007
Figure B01: Lead and crime rate
Adapted from Nevin, Rick, Environmental Research 104 (2007): 315-336
Secondary Air Pollutants
• Are produced in chemical reactions with
primary air pollutants
• Present harder-to-solve problems than
primary air pollutants
• Include acid deposition and photochemical
oxidants (smog)/ozone
Water Vapor, Clouds and Aerosol
• Warmer temperatures will lead to more water
vapor in the atmosphere because saturation
vapor pressure increases with temperature
– Extra water vapor is more greenhouse gas
– A positive feedback loop, more warming
– Enhanced cloudiness complicates this scenario
• Human activity leads to changes in cloudiness
– Contrails from aircraft
– Aerosols from ships contribute to cloudiness
– Aerosols from cities, ships act as CCN
Figure 03: Ship tracks
Courtesy of SSEC and CIMSS, University of Wisconsin-Madison
Figure 04: Contrails-- satellite
Courtesy of GeoEye and NASA. Copyright 2010. All rights reserved.
Figure 05: Saturation vapor pressure varies as a function of temperature
Acid Deposition
• Can be acid rain, snow, fog, dew, or dry
• Formed when oxides of nitrogen and sulfur
combine with water vapor or liquid water to
produce nitric acid and sulfuric acid
• In water, allows toxic heavy metals to leach
out and contaminate drinking water
• Damage to structures, make lakes toxic
Figure 06: pH scale
Courtesy of EPA
Figure 07: pH of rain
Photochemical Oxidants/Smog/Ozone
• Irritates eyes, nose, throat; causes coughing
chest pain, and shortness of breath,
aggravates asthma and bronchitis
• Forms when sunlight acts on a combination of
hydrocarbons, oxides of nitrogen, and oxygen
• Ozone is the main component, with PAN and
formaldehyde
The Stratospheric Ozone Hole
• Is reduced amounts of ozone over the
Antarctic in the decades since 1955
• Occurs in the Antarctic spring
• Is the result of the chlorine in CFCs
• Occurs because
• The Antarctic atmosphere is very cold
• Has polar stratospheric clouds
• The polar vortex prevents mixing
• Should improve in the next 50-100 years
Figure 08: The observed ozone minimum over Antarctica between 1955
and 2009
Modified from: GSFC/NASA
Figure 09: The daily minimum ozone values between 40°S and the
South Pole
Modified from: GSFC/NASA
Figure 10: The annual average size of the ozone hole
Modified from: GSFC/NASA
Desertification
• Is a spread of a desert region
• Is due to climate change
• Is due to human impacts on the land
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Overgrazing
Deforestation without reforestation
Diversion of water from a fertile region
Farming on unsuitable land (terrain, soil)
• Vulnerable areas include fringes of Sahara
desert, the Aral Sea, Lake Chad (West Africa)
Figure 11: Aral Sea, 1989 to 2008
Courtesy of the University of Maryland Global Land Cover
Facility/Landsat and MODIS/NASA
Urban Heat Islands
• Increased temperatures compared to rural
surroundings
• Greatest effect in summer and during the
night
• Due to human activities
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Industrial activity
Thermal properties of buildings and roads
Evaporation of water
Air conditioning and heating
Transportation
Figure 12: Urban heat island – conceptual model
Figure 13A: Urban heat Island – satellite
Courtesy of Robert Simmon, based on data from the National Land Cover
Database and Landsat 7/NASA
Figure 13B: Urban heat Island – satellite
Courtesy of Robert Simmon, based on data from the National Land Cover
Database and Landsat 7/NASA
Figure 14: Heat island – London
Adapted Chandler T.J. The Climate of London. Hutchinson, 1965
Figure 15: Magnitude of urban heat island
Courtesy of T. R. Oke, The University of British Columbia
Figure B02: Urban Heat Island and precipitation
Adapted from Shepherd, J.M., et al., Agronomy Monograph 55, (2010): 129 and J. Aitkenhead-Peterson and A. Volder (ed.). Urban Ecosystem
Ecology. American Society of Agronomy, 2010
Global Warming is a Fact!!!
• Over the past 2 decades the global average
surface temperature has increased noticeably.
• A trend involves a steady change in one
direction—upward for global average
temperature.
• Not every location and/or every region shows
the identical pattern.
Figure 16: Temperature departures from the global mean temperature over
land since 1880
Source: NASA/GISS
Figure 17: The annual temperature changes of the past 50 years
Courtesy of GISS/NASA
More Observations of Global Warming
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Widespread retreat of nonpolar glaciers
Thinning of arctic sea ice
Decreased N Hemisphere snow cover
Increase of global mean sea level
Longer growing season in NH
Shortened duration of ice cover on NH lakes
Figure 18: Sea level rise
Source: Intergovernmental Panel on Climate Change, "Climate Change 2007,”
The Fourth Assessment Report, Working Group 1, Figure 5.13; Red curve from:
Church and White, 2006; Blue curve from: Holgate and Woodworth, 2004; Black
curve from: Leuliette et al., 2004
Figure 19: SeaWiFS Ocean biology
Courtesy of GeoEye and NASA. Copyright 2010. All rights reserved.
Figure 20: Sea Ice change
Source: National Snow and Ice Data Center
Figure 21: Snow cover change
Courtesy of Riccardo Pravettoni, UNEP/GRID-Arendal
Figure 22: Lake Mendota ice cover
Source: Wisconsin State Climatology Office
Figure 23: Winter Temperature changes
Courtesy of NOAA/NCDC
Greenhouse Gases and Global
Warming
• Greenhouse gases include carbon dioxide,
water vapor, methane, CFCs and others
• Concentrations of carbon dioxide have
increased by 25% since the 19th century, and
increase by 0.5% per year
• More energy is trapped in Earth’s atmosphere
• Feedbacks are very important
• Scientists rely on complex computer models of
climate
Global Warming and the Oceans
• Oceans absorb energy trapped by increased
amounts of greenhouse gases
• Vertical motions in the atmosphere are very
sensitive to temperature
– Climate change can accelerate rapidly if global warming affects
convection in the oceans
• Oceans are full of life, which will be affected by
global warming
• Sea level is rising due to thermal expansion and
melting of ice sheets over land
Global Warming and the Cryosphere
• Cryosphere is the portion of Earth’s surface
covered by ice
• The cryosphere is shrinking
– Mountain glaciers are shrinking
– Arctic ice has thinned and covers a shrinking area at the end of
summer
– The Greenland ice sheet is melting rapidly
• Earlier snowmelt inhibits storage of water
• Lakes freeze/melt later/sooner and lose water
through evaporation
Global Warming and the Biosphere
• Biosphere comprises all of Earth’s living
organisms
• Tundra plants/animals are very sensitive to
changes in snow cover and temperature
• Gardeners notice changes in hardy zones
related to global warming
The IPCC
• IPCC is the Intergovernmental Panel on Climate
Change (over 1000 scientist)
– Formed by the United Nations’ World
Meteorological Organization (WMO) and the
Environment Programme (UNEP) in 1988
• Writes reports that describe our current
knowledge about climate change, based on
published scientific literature
• Has 90% confidence that observed temperature
rises are due to humans