Climate Change Science

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Climate Change Science
Glacier National Park, Montana
July 1932
July 1988

• Alan Cohn
• U.S. Environmental Protection Agency
• Hawaii Volcanoes National Park
• February 21, 2007

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Is there a greenhouse effect?

• Yes. Greenhouse gases effectively trap heat.
• Keeps average surface temperature warmer by
  60ºF

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A little bit of local history

• In the early 1960s, Charles Keeling began the
  first continuous recording of CO2 levels in the
  atmosphere atop Mauna Loa

http//www.aip.org/history/climate
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Have greenhouse gases increased as a consequence
of human activities?

• Greenhouse gases such as CO2, CH4, and N2O have
  increased considerably since 1750.
• Present CO2 and CH4 concentration levels highest
  in the last 650,000 years.

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Whos responsible for these emissions?

• Electricity, transportation, and industry
  biggest emitters
• When considering electricity distribution,
  homes and business account for a lot more

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Global CO2 Emissions
Data courtesy of Carbon Dioxide Information
Analysis Center, DOE
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Human Influence on the Atmosphere in the
Industrial Era
CO2 up 35
CH4 up 151
N2O up 18
Different symbols denote ice core data for
several sites in Antarctica and Greenland Source
IPCC WG I (Science) Summary for Policy-Makers,
Third Assessment Report, 2001.
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CO2 concentration is closely correlated with
temperature.
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Historic CO2 Concentrations
Today

Source IPCC WGI Third Assessment Report, 2001.
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Is the Earth warming?
(Relative to 1961-1990 Mean)

• Earths surface has warmed by about 1.4 º F since
  1860
• Most of this warming occurred post 1950
• Most of the warming of the last 50 years is very
  likely the result of human activities

Source Climate Research Unit, Univ. of East
Anglia UK Met. Office Hadley Centre, 2005.
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How much is the Earth warming?

• Eleven of the twelve years in the period
  1995-2006 rank among the 12 warmest since 1850.
• 2006 annual average temperature was warmest on
  record in U.S.
• Warming since the middle 1970s is now about 1F.
• Most areas have warmed
• Greatest warming Over land, northern high
  latitudes, nights, winter
• Observed increase in warm extremes, decrease in
  cold extreme

Source NASA, 2006.
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It is likely warmer now than it has been in at
least 2000 years.
Source Compilation of 10 peer reviewed
reconstructions, Wikipedia, 2006.
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Are greenhouse gases causing the Earth to warm?
"Most of the observed increase in globally
averaged temperatures since the mid-20th century
is very likely due to the observed increase in
anthropogenic greenhouse gas concentrations.
IPCC, 2007
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Additional Evidence of Warming Climate

• Earlier spring melting of ice on rivers and lakes
• Winter snow cover in the Northern Hemisphere is
  decreasing
• Increased ocean heat content is causing sea level
  to rise around the world

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Arctic sea ice is thinning and decreasing in
extent.
Sea Ice Minimum 2005
Sea Ice Minimum 1979

• Arctic is warming twice as fast as rest of the
  world.
• Arctic warming has worldwide implications.
• Indigenous people, animals and vegetation are
  affected.
• May open new shipping routes.

Source NASA, 2005
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Summer melting in Greenland has increased.
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Tropical and temperate mountain glaciers are
melting

• In Montanas Glacier National Park, 27 glaciers
  remain of 150 in 1850.
• Researchers have documented rapid mountain
  glacier retreat in Greenland, the European Alps,
  the Himalayas, Ecuador, Peru, Venezuela, New
  Guinea, and East Africa, among other places.

Qori Kalis Glacier, Quelccaya Ice Cap, Peru, are
shown between 1978 (top) and 2002. The glacier
retreat during this time was 1,100 meters.
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What about the future?

• Greenhouse gases and temperatures will very
  likely continue to increase.
• There are important uncertainties about future
  emissions and how the climate will respond to
  them.

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Sea Level will continue to rise.

• 1 to 3 foot rise possible by end of century.
• Will continue to rise even if temperatures stop
  rising.
• May rise more if warming accelerates melting of
  glaciers.

Source UK Met Office,Hadley Centre, 2002.
http//www.met-office.gov.uk/research/hadleycentr
e/pubs/talks/sld036.html
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Extreme Event Projections

• Higher maximum temperatures and more hot days and
  heat waves over land areas.
• Higher minimum temperatures and fewer cold days,
  frost days and cold waves.
• Source IPCC SPM, Third Assessment Report,
  Climate Change 2001 The Scientific Basis, 2001.

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Extreme Event Projections

• More intense precipitation events over many
  areas.
• Increase summer continental drying and associated
  risk of drought.
• Increase in tropical cyclone peak wind and
  precipitation over some areas.
• Source IPCC SPM, Third Assessment Report,
  Climate Change 2001 The Scientific Basis, 2001.

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For More Information
www.epa.gov/climatechange
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• Why do tenths of a degree matter?
• Global temp during Ice Age (20,000 years ago)
  were only 9F cooler than today
• What about the Medieval Warm Period?
• IPCC thinks it may have been limited to Europe
• Peak in solar activity
• What about the little Ice Age?
• Modest cooling of NH of less than 1C
• Decreased solar activity and increased volcanic
  activity
• What about volcanoes?
• Aerosols reflect sunlight
• Short term effects
• What difference does changing a light bulb make?
• If every household in the U.S. replaced one light
  bulb with an Energy Star qualified compact
  fluorescent light (CFL) bulb, it would prevent
  enough pollution to equal removing 1 million cars
  from the road

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The NAS on Global Warming

• Greenhouse gases are accumulating in the Earths
  atmosphere as a result of human activities,
  causing surface air temperatures and subsurface
  ocean temperatures to rise.

• The changes observed over the last several
  decades are likely mostly due to human
  activities, but we NAS cannot rule out that
  some significant part of these changes is also a
  reflection of natural variability.

Source Climate Change Science, National Academy
of Sciences, 2001.
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Caveats

• There are large uncertainties in the underlying
  assumptions about population growth, economic
  development, life style choices, technological
  change, and energy alternatives (NRC, 2001)
• Scenarios for future greenhouse gas amounts,
  especially for CO2 and CH4, are a major source of
  uncertainty for projections of future climate.
  (NRC, 2001)
• Because there is considerable uncertainty in
  current understanding of how the climate system
  varies naturally and reacts to emissions of
  greenhouse gases and aerosols, current estimates
  of the magnitude of future warming should be
  regarded as tentative and subject to future
  adjustments (either upward or downward). (NRC,
  2001)

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Future Scenarios

• The IPCC SRES (Special Report on Emissions
  Scenarios) scenarios cover a wide range of energy
  structures, reflecting uncertainties about future
  fossil fuel resources and technological change.
• 4 Scenario Families (6 scenario groups)
• 40 scenarios
• Storylines developed for scenario families that
  describe the future according to varying
  characteristics in
• Population Growth
• Carbon Intensity
• Environmental Awareness
• Economic Growth
• Land Use
• Within each family different scenarios explore
  variations of global and regional developments
  and their implications for greenhouse gas and
  sulfur emissions.

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Projections
Source IPCC Third Assessment Report, Climate
Change 2001 The Scientific Basis, 2001.
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Why do the effects of climate change vary by
region?

• Interactions between land and sea are complex.
• Changes to ocean circulation can lead to cooling
  in regions such as Europe as other areas get
  warmer.
• Other feedback mechanisms (ice-albedo, clouds)