attribution of changes

(Mt/Ag/EnSc/EnSt 404/504 - Global Change)(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9)Climate Models (from IPCC WG-I, Chapter 9)

Attribution of ChangesAttribution of Changes

Primary Source: Primary Source:

IPCC WG-I Chapter 9 - Understanding and Attributing Climate ChangeIPCC WG-I Chapter 9 - Understanding and Attributing Climate Change


What is climate?What is climate?

ClimateClimate is usually defined as the average weather, is usually defined as the average weather, or more rigorously, as the statistical description in or more rigorously, as the statistical description in terms of the mean and variability of relevant terms of the mean and variability of relevant quantities over a period of time ranging from quantities over a period of time ranging from months to thousands or millions of years. months to thousands or millions of years.

WMO period: 30 yearsWMO period: 30 years


What is climate change and variability?What is climate change and variability?Climate changeClimate change refers to a change in the state of the refers to a change in the state of the climate that can be identified (e.g., by using statistical climate that can be identified (e.g., by using statistical tests) by changes in the mean or variability of its tests) by changes in the mean or variability of its properties, and that persists for an extended period, properties, and that persists for an extended period, typically decades or longer.typically decades or longer.

Climate variabilityClimate variability refers to variations beyond refers to variations beyond individual weather events in the mean state and other individual weather events in the mean state and other statistics of the climate (such as standard deviations, the statistics of the climate (such as standard deviations, the occurrence of extremes, etc.) on all spatial and temporal occurrence of extremes, etc.) on all spatial and temporal scales. scales.

This includes “internal variability”.This includes “internal variability”.


What is detection and attribution?What is detection and attribution?

Detection Detection of climate changeof climate change is the process of is the process of demonstrating that climate has changed in some defined demonstrating that climate has changed in some defined statistical sense, without providing a reason for that statistical sense, without providing a reason for that change. change.

AttributionAttribution of causes of climate change is the process of of causes of climate change is the process of establishing the most likely causes for the detected establishing the most likely causes for the detected change with some defined level of confidence.change with some defined level of confidence.


Net RF: Net RF: 1750 to 20051750 to 2005(from Chapter 2)(from Chapter 2)

Note uncertaintiesNote uncertainties


Atmospheric Temperature Changes - PCM Modelsolar only volcanic only

GHGs only O3 only

direct sulphate aerosol

all

1890 to

1999 (˚C/100Y)


Reflected Solar RadiationReflected Solar Radiation

SatellitesModels

Deceasing Cloud Cover?


NH NH T: T: Reconstructions Reconstructions

vs. EBMvs. EBM


GCM Simulations: Natural ForcingsGCM Simulations: Natural Forcings

19 Simulations 5 Models


GCM Simulations: All ForcingsGCM Simulations: All Forcings58 Simulations

14 Models

Solar, volcanic effects?

Internal variability?

Aerosols?


Latitudinal Distribution of TrendsLatitudinal Distribution of Trends

Red:Red: All forcings, middle 90% of GCM range All forcings, middle 90% of GCM range

(58 simulations by 14 GCMs)(58 simulations by 14 GCMs)

Blue:Blue: Natural forcings only, middle 90% of GCM rangeNatural forcings only, middle 90% of GCM range

(19 simulations by 5 GCMs)(19 simulations by 5 GCMs)

Land & Ocean ChangesLand & Ocean Changes

IPCC:IPCC: Most global warming Most global warming very likelyvery likely due to increase in due to increase in anthropogenic GHG concentrationsanthropogenic GHG concentrations

Likely anthropogenic warming on continental scaleLikely anthropogenic warming on continental scale

IPCC Statement


Spatial Distribution of TrendsSpatial Distribution of Trends

58 Sim. 14

GCMs

19 Sim.

5 GCMs


Changes in Tropopause HeightChanges in Tropopause Height

ERA40: Observation-based analysisERA40: Observation-based analysis

Model results (each 4 simulations by PCM):Model results (each 4 simulations by PCM):

Red - All forcingsRed - All forcings Blue - Natural forcings onlyBlue - Natural forcings only


Ocean-Change Signal StrengthOcean-Change Signal Strength

Observed Signal: Red dotsObserved Signal: Red dots

Model results (individual basins from PCM):Model results (individual basins from PCM):

Green - All forcingsGreen - All forcings Blue - Natural forcings onlyBlue - Natural forcings only


Methods of Detection - Optimal FingerprintingMethods of Detection - Optimal Fingerprinting

Response patterns Response patterns to forcings - from a to forcings - from a GCMGCM

Observed climate Observed climate patternspatterns

Scale factorsScale factorsInternal variability Internal variability (“noise”)(“noise”)

Earlier slideEarlier slide

solar volcanic

GHGs O3

Aerosol All

Linear Linear RegressionRegression


Methods of Detection - Inferring ChangeMethods of Detection - Inferring Change

Are at least some of the scale factors Are at least some of the scale factors significantly different from zero?significantly different from zero? DETECTIONDETECTION

Is a forcing distinguishable from others? Is a forcing distinguishable from others? Can it (or some combination) explain Can it (or some combination) explain the observed pattern?the observed pattern?

ATTRIBUTIONATTRIBUTION


Scale Factors - 4 GCMsScale Factors - 4 GCMs

Bars: 5-95% uncertainty rangeBars: 5-95% uncertainty range

Red: GHGsRed: GHGs Green: Other human factorsGreen: Other human factors Blue: NaturalBlue: Natural


Inferred Climate Change - 4 GCMsInferred Climate Change - 4 GCMs

1990s minus 1900s1990s minus 1900s

(decades)(decades)

Trend: 1950 - 1999Trend: 1950 - 1999

Observed: Black lineObserved: Black line


Can Greenhouse Warming Cause Can Greenhouse Warming Cause a Climatic Extreme? a Climatic Extreme?

Summer temperatures in SwitzerlandSummer temperatures in Switzerland

A single event cannot be attributed to a forcing factor, A single event cannot be attributed to a forcing factor, butbut … …


Probability of extreme European summer temperatures(using the Hadley Centre GCM)

… … the the probabilityprobability (risk) of an occurrence can change due to (risk) of an occurrence can change due to external influences. external influences.

No anthropogenic change

With anthropogenic change


ENDEND

Attribution of ChangesAttribution of Changes

attribution of changes

Documents

global changeclimate

ipcc wg

global warming

negative forcings lead

inferred climate change

positive forcings lead

radiative forcings result

human activities