Detection of anthropogenic climate change

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Detection of anthropogenic climate change

• Gabi Hegerl,
• Nicholas School for the Environment and Earth
  Sciences,
• Duke University

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Temperature trend 1901-2000
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Fingerprint methods lin. regression

• Estimate amplitude of model-derived climate
  change signals X(xi),i1..n
• from observation y
• Best Linear Unbiased Estimator
• u noise residual
• (Hasselmann, 79 etc, Allen Tett, 99)
• Vector eg Temperature(space,time), scalar
  product Inverse noise covariance
• Signal pattern from model, amplitude from
  observation!

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June-July-August Greenhouse gas sulfate aerosol
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uncertainty range

• Estimated from coupled model internal variability
• Safety checks
• Use model with strong variability
• test consistency with observed noise residual u

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Contribution of greenhouse gas and sulfate
aerosols to to trend 1949-98
o Greenhouse gas sulfate aerosol simulation
Greenhouse gas only o/ inconsistent with
observation Ellipse 90 uncertainty range in
obs. Signal estimate from Hegerl and Allen, 2002
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The longer perspective
reconstruction of NH warm season temperature

Forced component Fat best fit to paleo Thin
5-95 range significant
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Conclusions global/NH SAT

• Significant climate change observed
• Uncertainty in distinction between forcings, but
• Most of the recent (last 50 yrs) global warming
  is likely due to greenhouse gases
• Significant and consistent climate signals in
  long temperature records

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Towards detection of anthropogenic changes in
climate extremes

• How to compare course-grid model with station
  data?
• Can daily data be substituted by monthly/annual
  and shift in distribution gt no
• Which index to use for early detection (avoid
  baseball statistics!) that is moderately robust
  between models? Change in once/few times/yr
  events robust and strong

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Changes in precipitation extremes stronger

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Change in rainfall wettest day/yr NAmerica
Consensus Observations show overall increase, too
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Annual mean precip changes consistent between two
models Wettest day/yr Wettest 5 consecutive
days
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Results Anthropogenic vs natural signals,
time-space
Bars show 5-95 uncertainty limits
Allen et al, 2002
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Annual mean rainfall change NAmerica
consensus