Download Climate Change A Statistician`s Perspective

Climate Change
A Statistician’s Perspective
Dennis Trewin
Statistical Consultant, Australia
Conclusions of the IPCC
• Support their conclusions on past climate
change and the impact of human activity
• Applaud the transparency of the report
• Compliment the degree of international
collaboration
• Concerned that there may be statistical
flaws in the projections of future climate
change
Conclusions from the IPCC
Summary for Policy Makers
• Increase of 0.5 degrees to 2030 (0.3 to
0.75) for all scenarios
• Accumulation of greenhouse gases is
important (suggesting earlier action)
• Best estimates of increase to the end of
the century range from 1.8 (B1 scenario)
to 4.0 (A1 scenario) degrees
Climate Change Scenarios
• A1 - very rapid economic growth, global
population peaking in mid century, economic
convergence, rapid introduction of new
technologies
• A1FI – fossil intensive
• A1T – non-fossil energy sources
• A1B – balanced
• A2 – heterogeneous world, regional based
development continually increasing population
Climate Change Scenarios
• B1 – Similar to A1 but change towards a
service and information economy with
reductions in material intensity
• B2 – Similar to A2 but population
increases at a slower rate and
intermediate levels of economic
development
My Concerns
• Non-use of purchasing power parities
(Castles/Henderson criticism)
• Convergence assumptions in A1 and B1
• High population growth assumptions in A2
and B2
• No estimates of robustness
• Insufficient information on distribution of
projections (addressed in the latest round)
Comparative Growth Rates
Scenario/Source
Annual Growth Rate (%)
A1
B1
US Dept of Energy
B2
World Bank
IEA
A2
3.1
2.4
1.9
1.8
1.8
1.5
1.0
Population Projections
• B2 is 13-19% higher than UN projections
• A2 is even higher
• A1 and B1 broadly consistent with UN
projections
Validity of the Scenarios
Best Estimates at 2100 and Range
• A1- unlikely because of very high economic growth
assumptions,
A1FI – 4.0 (2.4, 6.4)
A1B – 2.8 (1.7, 4.4)
A1T - 2.4 (1.4, 3.8)
• A2 – unlikely because of very high population growth
assumptions, 3.4 (2.0, 5.4)
• B1 – most likely but high economic growth because of
convergence assumptions, 1.8 (1.1, 2.9)
• B2 – unlikely because of very high population growth
assumptions, 2.4 (1.4,3.8)
B1 Estimates
Best Estimate
Temp Change
to 2030
Temp Change
to 2100
Sea Level Rise
to 2100
0.5
Likely Range
1.5
0.3-0.75
degrees
0.8-2.6 degrees
na
0.15-0.35 m
What would I advise policy
makers?
• Climate is extremely variable
• Global warming since 1900 with
associated sea rises; human activity is the
major contributing factor
• Distributional impacts of global warming
• Unless greenhouse gas emissions further
climate change and associated impacts
can be expected
What would I advise policy
makers?
• Best estimate until 2030 is temperature increase
of 0.5 degrees, sea level increase of 8 cms;
distributional impacts may be important
• B1 group of scenarios is most consistent with
authoritative assumptions on economic and
population growth
• A lot of uncertainity remains so take an adaptive
approach with some hedging for risk
Conclusion
• Should the OECD(?) develop climate
change projections using scenarios based
on authoritative economic and population
projections with appropriate use of PPPs?