Transcript John P. Holdren Assistant to the President for Science and

Climate-Change Science and Technology
What Do We Know? What Could We Do?
John P. Holdren
Assistant to the President for Science and Technology
and Director, Office of Science and Technology Policy
Executive Office of the President of the United States
Presentation for the
MEF
Washington, DC ▪ 27 April 2009
Coverage of these remarks
• The essence of the challenge
• Current insights from climate-change science
• The choices we face
• How much mitigation should we want?
• How big is the challenge of achieving this?
The energy-economy-climate challenge
is central to the human condition
because…
• Without energy there is no economy
• Without climate there is no environment
• Without economy & environment there is no
material well-being, no civil society, no security
Alas, the world is getting most of the energy its
economies need in ways that are wrecking the
climate its environment needs.
Current insights from climate science
• Climate change is happening faster than
previously predicted
emissions, concentrations, temperatures (regional &
global), & sea level all rising at rates at or above
those of earlier IPCC “high” scenarios
• Significant harm to human well-being is already
occurring
avoiding “dangerous” human interference is no longer
possible: we’re experiencing “dangerous” now
• Evidence is emerging that “tipping points” into
ecologically & societally disastrous changes
could occur sooner rather than later
Climate-change impacts already happening
• monsoon changes  agriculture impacts
• extreme precipitation  more floods
• ΔT + reduced precipitation in some regions &
more loss to storm runoff in others  increased
drought & soil drying
• ΔT & soil drying  increased wildfires
• ΔT  more heat stress and worse air pollution
• ΔT  pest population explosions  big timber
losses (Alaska, CO, CA...)
• tropical ocean ΔT is affecting corals (bleaching)
• increased integrated power of tropical storms is
probably linked to ocean ΔT
Bigger disruption is coming: IPCC 2007 scenarios
Last time T was 2ºC
above 1900 level was
130,000 yr BP, with
sea level 4-6 m higher
than today.
Last time T was 3ºC
above 1900 level was
~30 million yr BP, with
sea level 20-30 m
higher than today.
Note: Shaded bands
denote 1 standard
deviation from mean
in ensembles of model
runs
IPCC 2007
Emissions today are higher than even the highest
of the IPCC Scenarios
Source: Marland 2008, drawing from Raupach et al. PNAS 2007, Canadell et al. PNAS 2007.
Tipping points aren’t necessarily far off
• Arctic sea ice is shrinking much faster than
expected; if it disappears and doesn’t re-form,
climate of N hemisphere would change drastically.
• Rapid ice-sheet disintegration (1-2 m per century
sea-level rise) possible for ΔTavg ≥ 1.5ºC.
• Tundra & permafrost are warming & thawing, with
potential for CO2 and methane outpouring that
would accelerate climate disruption overall.
• Ocean acidification by dissolution of part of
excess atmospheric CO2 further stresses corals
as well as other ocean creatures that make
CaCO3 shells or skeletons.
What can be done?
There are 3 options:
• Mitigation, meaning measures to reduce the pace
& magnitude of the changes in global climate being
caused by human activities.
• Adaptation, meaning measures to reduce the
adverse impacts on human well-being resulting
from the changes in climate that do occur.
• Suffering the adverse impacts that are not avoided
by either mitigation or adaptation.
Mitigation possibilities
CERTAINLY
• Reduce emissions of greenhouse gases & soot
from the energy sector
• Reduce deforestation; increase reforestation &
afforestation
• Modify agricultural practices to reduce emissions
of greenhouse gases & build up soil carbon
CONCEIVABLY
• Create cooling effects offsetting greenhouse
heating
• “Scrub” greenhouse gases from the atmosphere
technologically
Adaptation possibilities include…
• Changing cropping patterns
• Developing heat-, drought-, and salt-resistant
crop varieties
• Strengthening public-health & environmentalengineering defenses against tropical diseases
• Building new water projects for flood control &
drought management
• Building dikes and storm-surge barriers against
sea-level rise
• Avoiding further development on flood plains &
near sea level
Some are “win-win”: They’d make sense in any case.
Mitigation & adaptation are both essential
• No feasible amount of mitigation can stop climate
change in its tracks.
• Adaptation efforts are already taking place and
must be expanded.
• But adaptation becomes costlier & less effective
as the magnitude of climate changes grows.
• The more mitigation can be achieved at
affordable cost, the smaller the burdens placed
on adaptation and the smaller the suffering.
How much mitigation, how soon?
• A number of studies have examined limiting ∆Tavg
to ≤2ºC.
• To gain a 50% chance of not exceeding this level
requires stabilizing the sum of human influences on
the atmosphere (CO2, other GHG, and atmospheric
particulate matter) at a level equivalent to 450 ppm
of CO2 (“450 ppm CO2-e”).
– In 2005 we were at 380 ppm CO2 and 430 ppm CO2-e from
all GHG combined.
– Effects of particles (warming from some, cooling from
others) added up to a net negative 50 ppm CO2-e, so total
human influence in 2005 was 430 – 50 = 380 ppm CO2-e.
Global CO2 emissions paths from 2000 for
stabilizing concentration at 450 ppm
▲
BAU emissions would
be ~15 GtC/yr in 2050
Details of paths depend on
differences & uncertainties in
treatment of global carbon cycle
and choices about how much to
do sooner vs later.
Grubb et al., The Energy Journal, 2006
Emissions growth 2000-2007 has closed
off some of the paths to 450 ppmv
• In order to stabilize CO2 at 450 ppmv, global emissions of
that gas from fossil fuels and deforestation combined now
must peak no later than 2020 and decline thereafter.
• Allowing for more emissions growth in developing countries
than in industrialized ones (as warranted by large current
gap in per-capita emissions), this means industrial country
emissions need to be declining by 2015 and developing
country emissions need to be declining by 2025.
• If non-CO2 greenhouse gases (CH4, N2O, halocarbons) &
absorbing particles are not reduced in proportion to
reductions in reflecting particles, requirement for CO2
reductions becomes more demanding.
Realities of reducing CO2 emissions
• Stabilizing at 450 ppmv CO2-e means 2050 global CO2
emissions must be ~7-9 GtC/yr below BAU.
• To understand the size of this challenge, consider some
examples of what avoiding 1 GtC/yr in 2050 requires…
- energy use in buildings cut 20-25% below BAU in 2050, or
- fuel economy of 2 billion cars ~60 mpg instead of 30, or
- carbon capture & storage for 800 1-GWe coal-burning
power plants, or
-1 million 2-MWe wind turbines replacing coal power plants
or
- 2,000 1-GWe(peak) photovoltaic power plants replacing
coal power plants
- cutting 2005 tropical deforestation rate in half worldwide
Socolow & Pacala, 2004