Climate Change:

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Climate Change Science and Skepticism Dr.
Kristy Dahl Rutgers Climate and Environmental
Change Initiative DeVry University February 21,
2008
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IPCC Assessments 1990-Present
1990 The unequivocal detection of the enhanced
greenhouse effectfrom observations is not likely
for a decade or more.
1995 The balance of evidence suggests a
discernible human influence on global climate.
2001 Most of the observed warming over the last
50 years is likely to have been due to the
increase in greenhouse gas concentrations.
2007 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.
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NASA/GISS http//data.giss.nasa.gov/gistemp/
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IPCC, 2007
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Blue Natural Pink Natural Human
IPCC, 2007
It is extremely unlikely that global climate
change of the past fifty years can be explained
without external forcing.
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The Greenhouse Effect
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Signs of warming Decreases in sea ice
National Snow and Ice Data Center, 2007
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Signs of warming Decreases in sea ice
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Signs of warming Sea Level Rise
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Future GHG emissions
IPCC, 2001
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Future Warming
IPCC, 2007
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Future Warming in Tri-State Area
Union of Concerned Scientists, NE Climate Impacts
Report, 2006
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Global Sea Level Rise
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Beyond Warming
Photos by Norb Psuty, Kevin Margitich
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Common Contrarian Arguments

• The current warming trend is part of a natural
  cycle
• The warming is being caused by water vapor
• CO2 and temperature are not in phase
• Some parts of the globe are warming
• Earth was warmer in the recent past (e.g. during
  the Medieval Warm Period)

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1. Is the current warming part of a natural cycle?
the Northern Hemisphere was warmer during the
last few decades of the 20th century than during
any comparable period over the preceding
millennium. -- National Research Council
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1. Is the current warming part of a natural cycle?
EPICA Ice Core Record, 2004
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2. Isnt water vapor a more important GHG than
CO2?
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3. In ice core records, doesnt CO2 lag
temperature?
EPICA Ice Core Record, 2004
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4. Arent some parts of the globe warming?
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4. Arent some parts of the globe warming?
IPCC, 2001
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5. Wasnt the Medieval Warm Period warmer than
today?
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5. OK, but isnt fixing this going to hurt our
economy?

• Stern Review
• To avert the worst effects of climate change, we
  need to invest 1 of global GDP per year
• McKinsey Global Institute
• A concerted, nationwide effort to reduce GHG
  emissions would almost certainly stimulate
  economic forces and create business opportunities
  that we cannot foresee today
• Almost 40 percent of abatement could be achieved
  at negative marginal costs.

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Photo by Andrew Davies
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R. Lathrop