Chapter 15Chapter 15

Human Influences on Climate

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 heatingCarbon 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

– 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– 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 – LondonAdapted 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): 1-29 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

• 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