John P. HoldrenAssistant 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

Climate-Change Science and Technology What Do We Know? What Could We Do?

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

Source: Marland 2008, drawing from Raupach et al. PNAS 2007, Canadell et al. PNAS 2007.

Emissions today are higher than even the highest of the IPCC Scenarios

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 possibilitiesCERTAINLY

• 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 & environmental-engineering 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.

Grubb et al., The Energy Journal, 2006

Details of paths depend on differences & uncertainties in treatment of global carbon cycle and choices about how much to do sooner vs later.

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

BAU emissions would be ~15 GtC/yr in 2050

▲

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 worldwideSocolow & Pacala, 2004