1. Detection of anthropogenic climate change
Gabi Hegerl,
Nicholas School for the Environment and Earth Sciences,
Duke University

2. Temperature trend

3. Fingerprint methods: lin. regression
Estimate amplitude of model-derived climate change signals X=(xi),i=1..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!

4. June-July-August Greenhouse gas + sulfate aerosol

5. uncertainty range Estimated from coupled model internal variability
Safety checks:
Use model with strong variability
test consistency with observed noise residual u

6. 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

7. The longer perspective
reconstruction of NH warm season temperature
Forced component
Fat: best fit to paleo
Thin: 5-95% range
*: significant

8. 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

9. 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 => 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

10. Changes in precipitation extremes stronger

11. Change in rainfall wettest day/yr NAmerica
Consensus
Observations show overall increase, too

12. Annual mean precip changes consistent between two models
Wettest day/yr
Wettest 5 consecutive days

13. Results: Anthropogenic vs natural signals, time-space
Bars show 5-95% uncertainty limits
Allen et al, 2002

14. Annual mean rainfall change NAmerica
consensus