To what extent is geo-engineering the solution to the climate change problem? Brian Hoskins Director, Grantham Institute for Climate Change Imperial College & Professor of Meteorology, University of Reading

“Greenhouse” gases determine height of layer from which heat escapes More greenhouse gases: higher level colder temperature less heat lost global warming (water vapour) carbon dioxide, methane,…

Temperature and greenhouse gases in past 650,000 y proxy for temp methane carbon dioxide nitrous oxide today time IPCC 2007

Causes of the current imbalance in the energy budget IPCC 2007

Since 1970, rise in:Decrease in:  Global surface temperatures NH Snow extent  Tropospheric temperatures Arctic sea ice  Global ocean temperaturesGlaciers  Global sea levelCold temperatures  Water vapour  Rainfall intensity  Precipitation in extratropics  Hurricane intensity  Drought  Extreme high temperatures  Heat waves Intergovernmental Panel on Climate Change Fourth Assessment Report (2007): “Global Warming is unequivocal” Estimates of NH temperatures in the past 1000 years

Projections of globally averaged surface warming IPCC 2007 Different scenarios

IPCC (2007) Surface Temperature Projections 2020s & 2090s relative to s2090s

Estimates of impacts in different sectors for increasing global warming (IPCC 2007)

Tackling the anthropogenic climate change problem By emitting greenhouse gases to the atmosphere we are perturbing the climate system in a dangerous way. What can we do? 1.Adapt to whatever happens: adaptation 2.Move towards a drastic reduction of the emissions of greenhouse gases: mitigation 3.Do something else to compensate: geo- engineering

Two basic kinds of geo-engineering 1.Reduce the content of greenhouse gases in the atmosphere 2.Alter the climate system

Geo-engineering 2 1.Reduce the atmospheric greenhouse gas content plant trees develop & grow special biological organisms fertilise the oceans

Oceanic carbon cycle

SeaWiFS Project,SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE. Biological activity in the ocean

Geo-engineering 2 2. Alter the climate system Restore the global energy balance by the management of solar radiation In terms of the global energy budget a reduction of the solar energy absorbed in the climate system by about 2% might balance a doubling of atmospheric carbon dioxide

Kiehl and Trenberth 1997 The Earth’s energy budget

1. In Space: Solar Interceptor Cloud of many small independent spacecraft. Each one has small solar sails to set its orientation to face the sun and to stay within the cloud, in line with sun (Angell, 2007) At a point where gravitational and centrifugal forces are in equilibrium (Lagrange point)

2. In the stratosphere, mimicking a volcanic eruption e. g. Mount Pinatubo in 1991 Pitari and Mancini (2002) Reduction in radiation Eruption1-year later Proposal: put SO 2 at about 25km in the equatorial region

3. Increase the reflection by low-level cloud Average amount of low-level (stratocumulus) cloud

3. Spray Turbine – Concept Latham Salter (2006)

4.Increase the reflectivity (albedo) of the surface 1.Whiten the desserts 2.Enhance reflectivity of human settlements 3.Develop & use more reflective grasses

Management of net Solar Radiation: Opportunities at 4 levels in the atmosphere Comments: 1.The restored energy balance through a reduction in solar radiation would be only in the annual and global average, not in a particular region or time of year 2.Solar and thermal radiation act on the climate system in different ways 3.Increasing acidification of the ocean would continue 4.Feasibility, cost, unintended impacts

Discussion 1.Our understanding of likely climate change due to increased greenhouse gases is limited. In general it is more so for geo-engineering “solutions”. 2.Need to be able to evaluate the actual impacts 3.Ability to stop quickly is an important consideration 4.Some private companies are already planning to start ocean fertilisation on a commercial basis, offering it as an off-setting mechanism 5.Is it a “solution”? Is it possible to compensate for any increase in atmospheric greenhouse gases? 6.Necessity for legal and political framework 7.Might it take the pressure off the imperative to reduce greenhouse gas emissions? 8.Is it a good way of buying time until serious greenhouse gas emission reductions have been agreed and executed?

Stabilisation CO 2 Concentrations and Emissions CO 2 concentration (ppm) CO 2 -equivalent concentration (ppm) Global mean temperature increase above pre-industrial level at equilibrium* (ºC) Peaking year for CO 2 emissions Global change in CO 2 emissions in 2050 (% of 2000 emissions) 350 – – – – to – – – – to – – – – to – – – – to – – – – to – – – – to +140 * Based on the “best estimate” of climate sensitivity. Source: IPCC (2007). © OECD/IEA 2007

Stippled areas are where more than 90% of the models agree in the sign of the change Precipitation increases very likely in high latitudes Decreases likely in most subtropical land regions This continues the observed patterns in recent trends Projected patterns at end of 21 st century: Change (%) in precipitation for one scenario June-Aug IPCC 2007 Dec-Feb

Possible CO 2 Emissions for 450ppm Stabilisation By 2030, emissions are reduced to some 23 Gt, a reduction of 19 Gt compared with the Reference Scenario Gt of CO 2 CCS in industry CCS in power generation Nuclear Renewables Switching from coal to gas End Use electricity efficiency End Use fuel efficiency Reference Scenario 450 Stabilisation Case 27 Gt 42 Gt 23 Gt Energy-Related CO 2 Emissions © OECD/IEA 2007

Tackling the anthropogenic climate change problem By emitting greenhouse gases to the atmosphere we are perturbing the climate system in a dangerous way. What can we do? 1.Adapt to whatever happens: adaptation 2.Move towards a drastic reduction of the emissions of greenhouse gases: mitigation 3.Do something else to compensate: geo- engineering

Stratospheric Circulation and Ozone distribution Proposal: put SO 2 at about 25km in the equatorial region