Download Imperial College London

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
Temperature and greenhouse gases in past 650,000 y
nitrous
oxide
carbon
dioxide
methane
proxy
for temp
time
today
IPCC 2007
Causes of the current imbalance in the energy budget
IPCC 2007
Intergovernmental Panel on Climate Change
Fourth Assessment Report (2007):
“Global Warming is unequivocal”
Estimates of NH
temperatures in the
past 1000 years
Since 1970, rise in:
 Global surface temperatures
 Tropospheric temperatures
 Global ocean temperatures
 Global sea level
 Water vapour
 Rainfall intensity
 Precipitation in extratropics
 Hurricane intensity
 Drought
 Extreme high temperatures
 Heat waves
Decrease in:
NH Snow extent
Arctic sea ice
Glaciers
Cold temperatures
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: geoengineering
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
Biological activity in the ocean
SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE.
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
The Earth’s energy budget
1
2
3
4
Kiehl and Trenberth 1997
1. In Space: Solar Interceptor
At a point where gravitational
and centrifugal forces are in
equilibrium (Lagrange point)
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)
1-year later
Eruption
Reduction in radiation
2. In the stratosphere, mimicking a volcanic eruption
e. g. Mount Pinatubo in 1991
Pitari and Mancini (2002)
Proposal: put SO2 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 deserts
2. Enhance reflectivity of human settlements
3. Develop & use more reflective grasses
Management of net Solar Radiation:
Opportunities at 4 levels in the atmosphere
Solar Radiation
Solar Interceptor
Top of
Atmosphere
Aerosol
Scattering
Cloud Albedo
SurfaceGrassland, Urbanization and Desert Albedo
Level 1 –
Space
Level 2 –
Stratosphere
Level 3 –
Troposphere
Level 4 Surface
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 CO2 Concentrations and Emissions
CO2-equivalent
concentration
(ppm)
Global mean
temperature
increase above
pre-industrial
level at
equilibrium*
(ºC)
Peaking year
for CO2
emissions
Global change
in CO2
emissions in
2050 (% of
2000
emissions)
350 – 400
445 – 490
2.0 – 2.4
2000 – 2015
-50 to -85
400 – 440
490 – 535
2.4 – 2.8
2000 – 2020
-30 to -60
440 – 485
535 – 590
2.8 – 3.2
2010 – 2030
+5 to -30
485 – 570
590 – 710
3.2 – 4.0
2020 – 2060
+10 to +60
570 – 660
710 – 855
4.0 – 4.9
2050 – 2080
+25 to +85
660 – 790
855 – 1 130
4.9 – 6.1
2060 – 2090
+90 to +140
CO2
concentration
(ppm)
* Based on the “best estimate” of climate sensitivity.
Source: IPCC (2007).
© OECD/IEA 2007
Possible CO2 Emissions for 450ppm Stabilisation
45
Energy-Related CO2 Emissions
42 Gt
CCS in industry
CCS in power generation
Nuclear
Renewables
Switching from coal to gas
End Use electricity efficiency
Reference Scenario
40
Gt of CO2
35
30
25
End Use fuel efficiency
27 Gt
450 Stabilisation Case
20
23 Gt
15
10
2005
2010
2015
2020
2025
2030
By 2030, emissions are reduced to some 23 Gt,
a reduction of 19 Gt compared with the Reference Scenario
© OECD/IEA 2007
Stratospheric Circulation and Ozone distribution
Proposal: put SO2 at about 25km in the equatorial region