John P. Holdren

1
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

2
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?

3
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.

4
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 were experiencing dangerous
  now
• Evidence is emerging that tipping points into
  ecologically societally disastrous changes
  could occur sooner rather than later

5
Climate-change impacts already happening

• monsoon changes ? agriculture impacts
• extreme precipitation ? more floods
• ?T reduced precipitation in some regions more
  loss to storm runoff in others ? increased
  drought soil drying
• ?T soil drying ? increased wildfires
• ?T ? more heat stress and worse air pollution
• ?T ? pest population explosions ? big timber
  losses (Alaska, CO, CA...)
• tropical ocean ?T is affecting corals (bleaching)
• increased integrated power of tropical storms is
  probably linked to ocean ?T

6
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
7
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.
8
Tipping points arent necessarily far off

• Arctic sea ice is shrinking much faster than
  expected if it disappears and doesnt re-form,
  climate of N hemisphere would change drastically.
• Rapid ice-sheet disintegration (1-2 m per century
  sea-level rise) possible for ?Tavg 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.

9
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.

10
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

11
Adaptation possibilities include

• Changing cropping patterns
• Developing heat-, drought-, and salt-resistant
  crop varieties
• Strengthening public-health environmental-engine
  ering 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 Theyd make sense in any
  case.

12
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.

13
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.

14
Global CO2 emissions paths from 2000 for
stabilizing concentration at 450 ppm

?
Details of paths depend on differences
uncertainties in treatment of global carbon cycle
and choices about how much to do sooner vs later.
BAU emissions would be 15 GtC/yr in 2050

Grubb et al., The Energy Journal, 2006
15
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.

16
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