Download Climate change

Attribution of Changes
Primary Source:
IPCC WG-I Chapter 9 - Understanding and Attributing Climate Change
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
What is climate?
Climate is usually defined as the average weather, or
more rigorously, as the statistical description in
terms of the mean and variability of relevant
quantities over a period of time ranging from
months to thousands or millions of years.
WMO period: 30 years
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
What is climate change and variability?
Climate change refers to a change in the state of the
climate that can be identified (e.g., by using statistical
tests) by changes in the mean or variability of its
properties, and that persists for an extended period,
typically decades or longer.
Climate variability refers to variations beyond
individual weather events in the mean state and other
statistics of the climate (such as standard deviations, the
occurrence of extremes, etc.) on all spatial and temporal
scales.
This includes “internal variability”.
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
What is detection and attribution?
Detection of climate change is the process of
demonstrating that climate has changed in some defined
statistical sense, without providing a reason for that
change.
Attribution of causes of climate change is the process of
establishing the most likely causes for the detected
change with some defined level of confidence.
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Net RF:
1750 to 2005
(from Chapter 2)
Note uncertainties
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Atmospheric Temperature Changes - PCM Model
solar only
volcanic only
GHGs only
O3 only
direct sulphate
aerosol
all
1890
to
1999
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
(˚C/100Y)
Climate Models (from IPCC WG-I, Chapter 9)
Reflected Solar Radiation
Satellites
Models
Deceasing Cloud Cover?
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
NH T:
Reconstructions
vs. EBM
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
GCM Simulations: Natural Forcings
19 Simulations
5 Models
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
GCM Simulations: All Forcings
58 Simulations
14 Models
Internal variability?
Aerosols?
Solar, volcanic effects?
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Latitudinal Distribution of Trends
Red: All forcings, middle 90% of GCM range
(58 simulations by 14 GCMs)
Blue: Natural forcings only, middle 90% of GCM range
(19 simulations by 5 GCMs)
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Land & Ocean Changes
IPCC Statement
IPCC: Most global warming very likely due to increase in
anthropogenic GHG concentrations
Likely anthropogenic warming on continental scale
Spatial Distribution of Trends
58
Sim.
14
GCMs
19
Sim.
5
GCMs
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Changes in Tropopause Height
ERA40: Observation-based analysis
Model results (each 4 simulations by PCM):
Red - All forcings
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Blue - Natural forcings only
Climate Models (from IPCC WG-I, Chapter 9)
Ocean-Change Signal Strength
Observed Signal: Red dots
Model results (individual basins from PCM):
Green - All forcings
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Blue - Natural forcings only
Climate Models (from IPCC WG-I, Chapter 9)
Methods of Detection - Optimal Fingerprinting
Linear
Regression
Observed climate
patterns
Scale factors
Response patterns
to forcings - from a
GCM
Earlier slide
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Internal variability
(“noise”)
solar
volcanic
GHGs
O3
Aerosol
All
Climate Models (from IPCC WG-I, Chapter 9)
Methods of Detection - Inferring Change
Are at least some of the scale factors
significantly different from zero?
DETECTION
Is a forcing distinguishable from others?
Can it (or some combination) explain
the observed pattern?
ATTRIBUTION
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Scale Factors - 4 GCMs
Bars: 5-95% uncertainty range
Red: GHGs
Green: Other human factors
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Blue: Natural
Climate Models (from IPCC WG-I, Chapter 9)
Inferred Climate Change - 4 GCMs
1990s minus 1900s
(decades)
Observed: Black line
Trend: 1950 - 1999
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Can Greenhouse Warming Cause
a Climatic Extreme?
Summer temperatures in Switzerland
A single event cannot be attributed to a forcing factor, but …
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Probability of extreme European summer temperatures
(using the Hadley Centre GCM)
No anthropogenic change
With anthropogenic change
… the probability (risk) of an occurrence can change due to
external influences.
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)
Attribution of Changes
END
(Mt/Ag/EnSc/EnSt 404/504 - Global Change)
Climate Models (from IPCC WG-I, Chapter 9)