Prof. Gerbrand Komen (ex-) Director Climate Research KNMI 20 November 2008 KNGMG Conference Climate...
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Transcript of Prof. Gerbrand Komen (ex-) Director Climate Research KNMI 20 November 2008 KNGMG Conference Climate...
Prof. Gerbrand Komen
(ex-) Director Climate Research KNMI
20 November 2008KNGMG Conference
Climate changefacts - uncertainties - myths
Variability
•Many mechanism with characteristic patterns and characteristic time scales
•Example: North Atlantic Oscillation
NAO Index - measuresair pressure difference between Iceland and the Acores
1. Use all available observations
2. Quantify processes, transports, interactions and feedbacks
Scientific approach
Natural archives (tree rings, ice cores, oceanic sediments, etc):
Instrumental observations (20th century)
Longer time scales provide important perspective
Because of the limited time I will focus on the past century
Observations: many time scales
Instrumental observations
Surface stations in the Global Observing System (GOS) of the Word Meteorological Organisation (www.wmo.ch)
Upper air observations inthe Global Observing System (GOS) of the World Meteorological Organisation (www.wmo.ch)
Voluntary Observing Ships in GOS
In the year 2007 : 383 ppm (37% above pre-industrial)
Example: annual mean precipitation
Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere
Land surfaceLand surfaceLand surfaceLand surfaceLand surface
Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice
Sulphateaerosol
Sulphateaerosol
Sulphateaerosol
Non-sulphateaerosol
Non-sulphateaerosol
Carbon cycle Carbon cycle
Atmosphericchemistry
1975 1985 1992 1997
Earth System Models
Th
e M
t.O
ffice
Had
ley
Cen
tre
Concerted efforts in Climate Model Diagnosis and Intercomparison
http://www-pcmdi.llnl.gov/
Average annual precipitation
Observations
Multi-model average
Global mean temperature in the 20th century model simulations vs observations
Natural causes: chaos, sun, ocean, orbital variations, volcanic dust . .
How does one establish a human influence: Greenhouse gases, Aerosols, Land surface change . .
a. Forcing with all known forcings
b. Forcing with natural forcings only
Compare model simulations with observations
Observations
All forcing
Solar + volcanic
Complex en unique system:
Observations
Model limitations
Sources of uncertaintySources of uncertainty
Limited understanding
Limited predictability
Most warming over the past 50 years is very likely due to anthropogenic GHG increases. Part of the variation can be accounted for by natural causes.
Δ T in 2100 (relative to 1990) is likely to lie between 1.1 en 6.4 °C
‘‘Quantifying’ uncertaintiesQuantifying’ uncertainties
Note: These probabilities involve a certain amount of (subjective) expert judgement
Robust: Global warming1, increase CO2
1, human influence2, expected future rise of mean temperature3, . .
Key uncertainties:Magnitude of expected change, trends in extremes,
regional change, feedbacks, role aerosols, Greenland (sea level rise!), . .
1. Based on observations2. Based on observation and interpretation with the
help of models3. Based on Greenhouse gas theory and models
Robust
1. Impacts on human society and biosphere
2. Reduction of vulnerability requires more adaptation - but there are limits to adaptability
3. Mitigation is possible
Key uncertainties
1. Costs: Unmitigated change, adaptation, mitigation
2. Best possible development path (energy innovation speed, adaptive capacity, governance, . .)
IPCC, possible responsesIPCC, possible responses
Forget uncertainties
Open mind Try to refute
Just curious . . . . . .
Policy relevant but not policy
prescriptive
. . . . . .
Influencepolicy
. . . . .
Taxonomy of actors in the climate Taxonomy of actors in the climate debatedebate
Alarmists Sceptics
Pure scientists
Honest broker
Climate science will never provide absolute certainty A description of current understanding is rather
complex (see summary in my summary) This complex message is often deformed in the
media and in the public debate Values play an important role in decision making Science should proceed as usual
Thank you !