The climate cooling potential of different geoengineering options - - PowerPoint PPT Presentation

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The climate cooling potential of different geoengineering options - - PowerPoint PPT Presentation

Jan 08, 2023 255 likes •563 views

The climate cooling potential of different geoengineering options Tim Lenton & Naomi Vaughan G eo E ngineering A ssessment & R esearch ( GEAR ) initiative School of Environmental Sciences, University of East Anglia, Norwich, UK

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GeoEngineering Assessment & Research

The climate cooling potential of different geoengineering options

Tim Lenton & Naomi Vaughan

GeoEngineering Assessment & Research (GEAR) initiative School of Environmental Sciences, University of East Anglia, Norwich, UK www.gear.uea.ac.uk

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GeoEngineering Assessment & Research

Overview Climate context Method Cooling potential Side effects Conclusion

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GeoEngineering Assessment & Research

Prevention versus medicine

Mitigation

  • Reducing greenhouse gas (especially CO2

) emissions Geoengineering “…large scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry.” National Academy of Sciences (1992)

  • 1. Solar radiation management
  • 2. Carbon dioxide removal
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GeoEngineering Assessment & Research

Future projections

IPCC (2007) = High growth = Mid growth = Low growth

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GeoEngineering Assessment & Research

Potential climate tipping points

Lenton et al. (2008) PNAS 105(6): 1786-1793

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GeoEngineering Assessment & Research

Some tipping points may be too close

Lenton and Schellnhuber (2007) Nature Reports Climate Change

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GeoEngineering Assessment & Research

Geoengineering options

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Geoengineering options

Reflect more sunlight back to space Remove CO2 from atmosphere and store it

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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How to quantify and compare them?

GeoEngineering Assessment & Research

Use radiative forcing (RF in W m-2)

Linearly related to surface temperature change Ts =  RF

Uncertain climate sensitivity parameter

 = 0.6 – 1.2 K W-1 m2 (best guess  = 0.86)

Useful reference points:

Current anthropogenic RF ~ 1.6 W m-2 Doubling CO2 gives RF = 3.71 W m-2

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Solar radiation management

Increase surface albedo Increase cloud albedo Stratospheric aerosols Sunshades

Reflect more sunlight back to space

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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Quantification

GeoEngineering Assessment & Research

Radiative forcing at top of atmosphere

Depends on change in planetary albedo

Change in planetary albedo depends on:

Albedo change of layer affected Fraction of Earth’s area affected Prior absorption/reflection Changes in subsequent absorption/reflection

Use global mean energy balance (land or ocean)

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Reduce sunlight reaching the surface

Sunshades Increase cloud albedo Stratospheric aerosols

Sunshades Stratospheric aerosols Cloud albedo

  • CCN biological, mechanical

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Sunshades in space At L1 point (Angel 2006)

4.7 million km2

Multiple ‘flyers’ ~0.3m2

800,000 flyers/launch

Just to counteract CO2 rise of 2 ppm yr-1 requires:

35,700 km2 yr-1 ~150,000 launches yr-1

Cartoon of reflectors in space

RF = -3.71 W m-2 In principle but not in practice

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GeoEngineering Assessment & Research

Stratospheric aerosol injection Depends on aerosol type, amount, effective radius Inject into lower stratosphere over tropics 1.5–5 Mt S yr-1 to offset doubling CO2

c.f. current ~50 Mt S yr-1 added to troposphere

Stratospheric aerosols injection Mt Pinatubo eruption 1991

RF = -3.71 W m-2 Feasible

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GeoEngineering Assessment & Research

Enhancing cloud albedo Cloud albedo depends on density of cloud droplets Enhance this by adding condensation nuclei

Sea salt, dimethyl sulphide

Sensitivity depends on:

Hygroscopicity of aerosol Optical depth of cloud Changes in entrainment…

Mechanically enhance cloud albedo – Stephen Salter

RF = -3.71 W m-2 Feasible but uneven

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GeoEngineering Assessment & Research

Increase reflection at the surface

Increase surface albedo

Cropland, Grassland Urban, human settlement Desert

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Increase surface albedo Desert

Reflective cover over

Cropland, grassland

Variegated species, light shrubs, leaf waxes

Human settlement, urban areas

Paved surfaces, roofs… Urban heat island

50% global population

Reflective roof surfaces – Californian legislation

Urban RF = -0.047 W m-2

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GeoEngineering Assessment & Research

CO2 removal from the atmosphere

Enhance downwelling Carbonate addition Enhance upwelling Nutrient addition Afforestation & reforestation Bio-energy capture Air capture Biochar

Remove CO2 from atmosphere and store it

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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Quantification

GeoEngineering Assessment & Research

Radiative forcing a logarithmic function of CO2

RF = 5.35 ln(CO2 /CO2 ref ) Must specify reference concentration; CO2 ref

Any perturbation to atmospheric CO2 decays away

  • ver time due to exchange with the ocean and land

f(t) = 0.18 + 0.14 e–t/420 + 0.18 e–t/70 + 0.24 e–t/21 + 0.26 e–t/3.4

Removal flux of CO2 is itself a function of time

Must specify timescale of interest, chose 2050 and 2100

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Removal of CO2 - Land

Enhance downwelling Carbonate addition Enhance upwelling Nutrient addition Afforestation & reforestation Bio-energy capture Air capture Biochar

BioEnergy Capture & Storage Air capture - ‘Artificial trees’ Biochar Afforestation

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Air capture and storage of CO2

Chemical air capture

More costly

Biomass energy with carbon capture & storage (BECS) Maximum estimate

Biofuels replace oil in transport Biomass replaces coal for electricity production 11.8 PgC yr-1 in 2100 771 PgC stored by 2100

Direct air capture – Klaus Lackner’s ‘artificial trees’

RF (2050) = -0.74 W m-2 RF (2100) = -2.5 W m-2

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GeoEngineering Assessment & Research

Pyrolysis

converts up to 50% of carbon in biomass to charcoal

Maximum estimate

0.56 PgC yr-1 at present Scaling up using biomass energy production 3.15 PgC yr-1 in 2100

Total biochar reservoir

148 PgC by 2100 Long term storage potential:

224 PgC global cropland 175 PgC temperate grassland

Biochar – biomass burnt in near zero oxygen (pyrolysis)

Biochar CO2 removal

RF (2050) = -0.12 W m-2 RF (2100) = -0.40 W m-2

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GeoEngineering Assessment & Research

Removal of CO2 - Ocean

Enhance downwelling Carbonate addition Enhance upwelling Nutrient addition Afforestation & reforestation Bio-energy capture Air capture Biochar

Addition of Iron, Nitrate, Phosphorus Ocean pipes Add carbonate Increase downwelling

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Ocean fertilisation

Macronutrient addition

Nitrate, Phosphate

Micronutrient addition

Iron fertilisation 12 Fe-addition patch experiments to date

Assume removal of iron limitation globally

Consider increase of sinking

  • rganic carbon flux below

the depth of winter mixing

Iron addition to Fe-limited surface waters to stimulate productivity

Iron Fertilisation RF (2050) = -0.11 W m-2 RF (2100) = -0.20 W m-2

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GeoEngineering Assessment & Research

Radiative forcing potential (in 2100)

  • 0.002
  • 0.025
  • 0.003
  • 0.20
  • 0.15
  • 0.37
  • 0.40
  • 2.5

All blue values are in W m-2 +3.1 W m-2 500 ppm

  • 0.2
  • 2
  • 0.3
  • 19
  • 14
  • 34
  • 37
  • 186

All green values are in ppm of CO2 >-3.1 >-3.1 ~-3.1

  • 2.1 desert
  • 0.51 grassland
  • 0.35 cropland
  • 0.15 settlements
  • 0.05 urban areas

~-3.1

Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

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GeoEngineering Assessment & Research

Radiative forcing potential

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GeoEngineering Assessment & Research

Radiative forcing potential

1.6 3.7

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GeoEngineering Assessment & Research

Side effects of reflecting sunlight

Weakens the water cycle

Promotes drought in monsoon regions e.g. India

Commitment to long-term maintenance

Sudden stop of activity causes rapid warming

Ocean acidification

Does not address this impact (may increase it)

Regional climate changes

Residual differences in global climate

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GeoEngineering Assessment & Research

Side effects of CO2 removal

Land

Possible conflicts with other land uses Other greenhouse gases and albedo effects

Ocean

Ecosystem impacts Difficult verification and monitoring

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GeoEngineering Assessment & Research

Conclusion

Climate change is a problem of risk management

Already a risk of dangerous climate change even with strong mitigation Need to weigh up the risks of using or not using geoengineering

2 types of geoengineering with very different side effects and risks Sunlight reflection options could be reserved for use in emergency Carbon dioxide removal could complement mitigation efforts It is the only way to return to the pre-industrial atmospheric CO2 level