Burning issues at climate
science – policy interface
Judith Curry
Agreement:
• Surface temperatures have increased since 1880
• Humans are adding carbon dioxide to the atmosphere
• Carbon dioxide and other greenhouse gases have a
warming effect on the planet
Disagreement:
• Whether the warming since 1950 has
been dominated by human causes
• How much the planet will warm in the
21st century
• Whether warming is ‘dangerous’
• Whether we can afford to radically
reduce CO2 emissions, and whether
reduction will improve the climate
21st
Burning issues at the interface
between climate science and policy
Social cost of carbon: economic costs of CO2, and benefits
of CO2 reduction
Evolution of 21st climate: how much warming, and when?
Impact of proposed policies on 21st century climate change.
On trial in MN:
Social Cost of Carbon
A 1990s law requires the PUC to establish externality
values for CO2 and other power plant pollutants to help
guide utility planning decisions.
The PUC adopted the federal Social Cost of Carbon
(SCC)
SCC is being challenged by energy companies and
industry groups in a current trial
Equilibrium Climate Sensitivity
Definition: Global surface temperature change following a
doubling of atmospheric CO2 concentration
Determined from:
• global climate models
• historical observations
• paleoclimate
reconstructions
How much warming will emissions reductions
commitments prevent in the 21st century?
U.S.: (calculations by CATO: ECS=3oC)
• Reducing U.S. total emissions by 80% by 2050 will
prevent 0.11oC in warming by 2100
Global estimates (in progress)
• 0.2oC is optimistic target
• India’s INDC will double - triple
emissions by 2030
Implications for the future:
I. IPCC AR5 view
AR5 2013
The amount of warming depends on
the emission of greenhouse gases
Growing divergence: models vs observations
• Are climate models too sensitive to greenhouse forcing?
• Is modeled natural climate variability inadequate?
• Are model projections of 21st century warming too high?
Scenarios of future climate
CO2 emissions
Long range
ocean oscillations
Geologic
processes
Solar effects
Volcanic
eruptions
Unknowns
50 YEARS, 100 YEARS
Implications for the future:
II. View emphasizing natural variability
• The rate of warming will be slow for at least another
decade (into the 2030’s?); ocean circulation patterns
• Climate models are too sensitive to human forcing;
21st century warming will be on the low end of IPCC
projections (or even below)
• Solar variations & volcanoes: wild card. Some
are predicting major solar cooling in the near term
• Can’t rule out unforeseen surprises
What does climate science say about
policy and mitigation solutions?
• There is increasing evidence that the threat
from global warming is overstated
• However, if the threat is not overstated, there
are major shortfalls in current and proposed
solutions.