Climate Engineering“

1. Introduction

Ulrich Platt Institut für Umweltphysik Lecture Program of „Climate Engineering

Part 1: Introduction to the Climate System (4 sessions) 1. Introduction and scope of the lecture 2. The Climate System – Radiation Balance 3. Elements of the Climate System - Greenhouse Gases, Clouds, Aerosol 4. Dynamics of the Climate System - Sensitivity, Predictions Part 2: Climate Engineering Methods - Solar Radiation Management, SRM 1. SRM – Reflectors in space 2. SRM – Aerosol in the Stratosphere 3. SRM – Cloud Whitening 4. SRM – Anything else Part 3: Climate Engineering Methods – Carbon Dioxide Removal, CDR

1. Direct CO 2 removal from air 2. Alkalinity to the ocean (enhanced weathering) 3. Ocean fertilization 4. Removal of other greenhouse gases Part 4: CE – Effectiveness, Side Effects (3 sessions) 1. Comparison of Techniques, characterisation of side effects 2. Other parameters than temperature 3. Summary 2 Contents of Today's Lecture

• Global Warming - „Climate Change“ • What is Climate Engineering • Why Climate Engineering? • Physics of Climate – which knobs to turn? • „Leverage“ of CE-Techniques • Techniques to influence the climate, examples • Even stranger ideas • Conclusion Literature

Bodansky, D. (1996), 'May we Engineer the Climate?', Climatic Change 33 , 309-321. Boyd, P. W. (2008), 'Ranking geo-engineering schemes', Nature Geoscience 1, 722-724. Cicerone, R. J. (2006), Geoengineering: Encouraging research and overseeing implementation, National Academy of Sciences, Washington DC, chapter Climatic Change, pp. 221-226. Crutzen, P. J. (2006), 'Albedo Enhancement by Stratospheric Sulfur Injections: A Contribution to Resolve a Policy Dilemma?', Climatic Change 77(3-4), 211--220. Feichter, J. & Leisner, T. (2009), 'Climate engineering: A critical review of approaches to modify the global energy balance', The European Physical Journal - Special Topics 176(1), 81--92 Hegerl, G. C. & Solomon, S. (2009), 'Risks of Climate Engineering', Science 325, 955-956. IPCC Climate Change 2014 Synthesis Report: https://www.ipcc.ch/site/assets/uploads/2018/02/SYR_AR5_FINAL_full.pdf Lamb, H. H. (1971), 'Climate-Engineering Schemes to meet a Climatic Emergency', Earth-Science Reviews 7, 87-95. Lenton, T. M. & Vaughan, N. E. (2009), 'The radiative forcing potential of different climate geoengineering options', Atmos. Chem. Phys. 9, 5539-5561. Robock, A. (2008), '20 reasons why geoengineeringmay be a bad idea', Bulletin of the Atomic Scientists 64(2), 14-18. Society, The Royal (2009), Geoengineering the climate: Science, governance and uncertainty', Technical report, The Royal Society (RS Policy Document 10/09 ). Wood, L.; Hyde, R. & Teller, E. (1997), 'Global Warming and Ice Ages: I. Prospects for Physics-Based Modulation of Global Change'. Ross A & Matthews HD (2009) Climate engineering and the riskof rapid climate change. Environmental Research Letters 4, 045103 doi: 10.1088/1748-9326/4/4/045103 Web – Pages of Interest

Heidelberg Marsilius Project on Climate Engineering: http://www.climate-engineering.uni-hd.de/projects/ Asilomar Conference on Climate Intervention Techniques: http://www.climateresponsefund.org/ Report: Climate Engineering Responses to Climate Emergencies: http://arxiv.org/ftp/arxiv/papers/0907/0907.5140.pdf Report of the Britischen Royal Society on CE: http://royalsociety.org/policy/publications/2009/geoengineering-climate/ David Keith‘s Home Page: http://keith.seas.harvard.edu/ Alan Robock‘s Home Page: http://www.envsci.rutgers.edu/~robock/ Intergovernmental Panel on Climate Change, IPCC: https://www.ipcc.ch/ YouTube CE-Playlist (CE-Related Video Clips): http://www.youtube.com/playlist?list=PLF8369A27273 314D8

Provided by: Andrew Lockley Interventions into the Climate System ? Assessing the Climate Editors: Engineering Debate Wilfried Rickels, Gernot Klepper, and Jonas Dovern Authors: Gregor Betz, Nadine Brachatzek, Sebastian Cacean, Kerstin Güssow, Jost Heintzenberg, Sylvia Hiller, Corinna Hoose, Gernot Klepper, Thomas Leisner, Andreas Oschlies, Ulrich Platt, Alexander Proelß, Ortwin Renn, Wilfried Rickels, Stefan Schäfer, Michael Zürn From the Preface: …. Climate engineering raises numerous questions of fundamental importance: Which proposals are scientifically realistic? Can they be technically implemented, and how effective are they likely to be? What interactions and side-effects (e.g., in the climate system) are to be expected? How far do the efficiency advantages of individual measures go in a comprehensive macro- economic consideration? Will climate engineering become an endurance test for society and international relations? Is selective intervention in the Earth system ethically acceptable or justifiable? … 2011 Dr. Georg Schütte State Secretary at the Federal Ministry of Education and Research (BMBF) Climate Engineering (frequently also called „Geoengineering “)

Intentional, large scale manipulation of the environment to counteract the unintended effects of anthropogenic climate change (D. Keith, 2000).

Absichtliche, großskalige Manipulation der Umwelt, um unerwünschten Effekten des anthropogenen Klimawandels entgegenzuwirken (D. Keith, 2000)

Questions: 1) Is it actually possible and (if yes) affordable? 2) If 1) should be true, should we actually do it? 3) What are the side effects? Geoengineering

Blasphemous - How can we dare to interfere with nature (or God)? Hubris - How can we think that everything can be accomplished by technology? yet

We are modifying our climate already – not intentionally though - e.g. by releasing greenhouse gases to the atmosphere The History of Weather Control

http://www.terraforminginc.com/weather-control/ Modifying Weather and Climate? History of CE-Proposals (1)

Source: Climate engineering, Technical status, future directions, and po tential responses Center for Science, Technology, and Engineering United States Government Accountability Office, GAO, July 2011, GAO-11-71 September 29, 1921: End Of Iceberg Menace! Nuke the Arctic Professor Julian Huxley. “Can We Atomize the Arctic?”, Jan. 1945

Wallace W. Ashley and Elmer V. Swan. According to them, Professor Julian Huxley had proposed the idea of using nuclear bombs to melt the polar ice caps. This would moderate our northern climate, eliminating pesky cold snaps and opening up shipping across the top of the world. History of CE-Proposals (2)

Source: Climate engineering, Technical status, future directions, and potential responses, GAO, July 2011, GAO-11-71

History of CE-Proposals (3)

Source: Climate engineering, Technical status, future directions, and potential responses, GAO, July 2011, GAO-11-71

The Atmospheric CO 2 – Mixing Ratio During the last 60 Years

CO 2-fraction 2.4 ppm/Yr. in dry air, µmole/mole or ppm 400

380

360

340

320 Charles D. Keeling (1928-2005)

0.8 ppm/Yr. Scripps Mauna Loa, Hawaii, USA, 3397m a.s.l. Source: World Meteorological Organization (WMO) Cumulative Anthropogenic Carbon Emission to the Atmosphere 1850-2006 (in units of 10 9 tC)

By 2011:  360 GtC equiv. to 1.3 10 22 J Heat Air by 3K Average Power: 510 -3W

Source: Carbon Dioxide Information Analysis Center (CDIAC.com) and values of atmospheric CO 2 concentrations from Mauna Loa, as well as other locations. Carbon emissions from land use change and deforestation not included. Global Annual Mean Surface Air Temperature Change

Tropospheric aerosols mask warming (global dimming)

Greenhouse gases dominate

Recovery from volcanic eruptions dominates

http://data.giss.nasa.gov/gistemp/graphs/Fig.A2.pdf The Challenge: Limit CO2-Growth

Constant emissions at 2010 rate

33% of 2010 rate

10% of 2010 rate

0% of 2010 rate

From: Klaus Lackner Will We Manage to Reduce CO2 – Emissions? Will We Manage to Reduce CO 2 – Emissions? Example: Germany

Mt CO 2equiv. 100% Emission of greenhouse gases regulated by UNFCC

-31%

-40%

-55%

-70%

-95% Radiative Climate Forcing Components

Source: IPCC-AR5, Fig. SPM.5 Problem beyond Gradual Changes : „Tipping Elements“

Timothy M. Lenton, Hermann Held, Elmar Kriegler, Jim W. Hall, Wolfgang Lucht, Stefan Rahmstorf, and Hans Joachim Schellnhuber (2008), Tipping elements in the Earth’s climate system, PNAS 105(6), 1786–1793.

Climate subsystems where anthropogenic climate forcing could cause threshold-type behavior.  small perturbation at a critical point qualitatively alters the future fate of the system. They could be triggered this century and would undergo a qualitative change within this millennium. (“Tipping Elements” in colour, overlain on global population density) Climate Change – what to do?

Mitigation (Abwendung ) Adaptation (Anpassung ) Rapid reduction of Relocate population, greenhouse gas emissions change structure of agriculture, higher levies...

Climate Engineering Reduction of solar radiation, removal of greenhouse gases from the atmosphere, … From: nature reports climate change, Vol. 4, p. 5, Jan. 2010, Climate Engineering

• Serious discussions since about the mid-1960ties (basic ideas shade sun, raise Earth‘s albedo) • Increasing number of publications since about 2006 • Today there are many proposed techniques, more and more problems are noticed Historical Background

- “Can We Atomize the Arctic?”, Jan. 1945, Prof. Julian Huxley Idea of using nuclear bombs to melt the polar ice caps. This would moderate the northern climate, eliminating pesky cold snaps and opening up shipping across the top of the world.

- Weather and precipitation control for commercial and military purposes (USA, UdSSR, China, 1950 ~ 1980) As our civilization steadily becomes more mechanized and as our population density grows the impact of weather will become ever more serious. ...The solution lies in ... intelligent use of more precise weather forecasts and, ideally, by taking the offensive through control of weather... I shudder to think of the consequences of a prior Russian discovery of a feasible method for weather control. Henry Houghton, MIT, 1957

- Geoforming, Geoengineering Bering straight - dam or diversion of large sibirian rivers for irrigation of central asia make the North Polar See ice-free P.M. Borisov, Bulletin of the Atomic Scientists , March, 1969, pp. 43-48 Geo-Engineering Intentional change of climate parameters (to compensate for the consequences of the antropogenic greenhouse effect)

P. Crutzen Climatic Change, 2006 34 Sa ve Th Forget about a future fillede with wind farms and hydrogenWo cars. The Pentagon's top weaponeerrld? says he has a radical solution that would stop global warming now -- no matter how much oil we burn.

Jeff Goodell Rolling Stone November 3, 2006 Attempting to Modifying the Climate - Why?

• Annual anthropogenic emissions: 9 Gt of carbon (equivalent to 33

Gt of CO 2) • It is clear that our climate is changing and will even more rapidly change in the coming decades (if projections are correct). • Stabilizing the atmmospheric CO 2 level would require about 80% cut in global emissions. • Negotiations to reduce CO 2-emissions have had dissapointing results • In addition there is the danger of „Tipping Elements“ So our options appear to be: • Adapt to climate warming or • Actively change the climate Some Question s:

• Is CE technologically feasible? • Do we actually need to apply CE? • Who decides on application of CE? • Who decides on the global temperature? Reasons why Geoengineering may be a Good Idea

1. Cool the planet 2. Reduce or reverse ice melting 3. Reduce or reverse land ice sheet melting 4. Reduce or reverse sea level rise 5. Increase plant productivity

6. Increase terrestrial CO2 sink

Robock et al. 2009, GRL Reasons why Geoengineering may be a Bad Idea 1. Effects on regional climate (temperature, precipitation, other para.) 2. Continued ocean acidification 3. Rapid warming when CE stops 4. Stratospheric Ozone depletion 5. Effects on plants (less solar radiation and lower direct/diffuse ratio) 6. Enhanced acid precipitation 7. Whitening of the sky (but nice sunsets) 8. Effects on cirrus clouds as aerosols fall into the troposphere 9. Less solar radiation for solar power (especially less direct radiation) 10. Environmental impacts of aerosol injection (production and delivery) 11. There’s no going back (how rapidly could effects be stopped?) 12. Human error 13. Undermining emissions mitigation. 14. Cost 15. Commercial control of technology Robock, Alan, 2008: 20 reasons 16. Military use of technology why geoengineering may be a 17. Conflict with current treaties bad idea. Bull. Atomic Scientists , 64 , No. 2, 14-18, 59, 18. Control of the thermostat? doi:10.2968/064002006. 19. Question of moral authority 20. Unexpected consequences Two Types of „Climate Engineering“

Greenhouse gases reduce IR-emission

1) Solar radiation management (SRM) 2) Carbon cycle engineering (CDR)

• Sulfate aerosol in the stratosphere • Direct capture of CO 2 from air • Cloud whitening • Ocean fertilization • Change surface albedo of Earth • Alkaline material into the ocean and/or ocean • bury charcoal „Bio-char“ • Special particles in the mesosphere • Alkaline material into the soil • Scatterers in space Slow and expensive ,

Fast, cheap, imperfect and unsafe , little But the cause (the CO 2) is actually influence on atmospheric CO 2 removed from the air The „Leverage“ of CE - Techniques Leverage Ratio: Mass of Greenhouse Gas the effect of which is neu tralized R  Lev Mass of material needed for the measure

Examples:

1) Mankind emitted about 370 Gt carbon (1357 Gt CO 2) since 1750. About 1 Mt of sulfur would be required to offset the warming effect of that much CO 2 (for one year) 6  Rlev  1.4 10

2) In order to induce ocean uptake of the same amount of CO 2 about 3100 Gt of CaCO 3 (carbonate) would be required  Rlev  0.44

(CO 2 + CaCO 3 + H 2O  Ca(HCO 3)2) 3) Iron Fertilization of the ocean requires 1 atom of Fe for 10 5 atoms of C in algal 4 biomass (Redfield ratio)  mass ratio Rlev  2.5 10 Climate-Engineering (Geo-Engineering)

Simple Global Radiation Balance: 4 4 2L S0 21  A  TS 2 T A  2A 2  A

Reduction of atmospheric (IR) Increase of Planetary Albedo (A) Change of Solar constant (S 0) absorption (A)

• • • Scattering surfaces in the Scattering surfaces in space Geochemical CO 2 – stratosphere sequestration in the ocean (e.g . sulfate aerosol ) • Ocean Fertilization • Absorber in the Stratosphere • CO 2 – sequestration from the • Scattering surfaces in the air (air capture ) Troposphere • CO – uptake by terrestrial (e.g . whiter clouds ) 2 ecosystems • Change of Albedo of Land - (new forests , biochar ) and Ocean – surfaces

Adapted from Thomas Leisner 42 Climate-Engineering Climate Engineering Techniques ... Are there no T.M. Lenton and N.E. Vaughan, The radiative forcing better ideas? potential of different climate geoengineering options, Atmos. Chem. Phys., 9, 5539–5561, 2009 SRM

CDR

Keith, David, 2001: Geoengineering, Nature , 409 , 420. 45 Change of the Solar constant: (Angel, PNAS, 2006)

1. Site: 1. Lagrange-point (L1-point) (unstable)

ME 2. Implementation: Cloud of many thin discs, stabilised by modulation of radiation pressure, disk size: ~1 m, 13 r Weight: 1g, Number: 1.6 10 3. Optical Design: Transparen refracting material, low areal density, total mass: 20 Mt rE 4. Transport: elektromagnetic accelerator, Ionen thrusters, Cost: 50 $/kg (zur Zeit 20000 $/kg)

Total cost several Trillion $ (100 billion $/a) How much shading is Needed?

Example: We whish to offset temp. change due to 2xCO: Primary forcing: 3.7 W (there will be little or no feedback if we compensate primary forcing) Incident Radiation on Earth: 1372 W/m2 minus reflection (A=0.7): 960 W/m2 We need to shade an area of: 3.7/960 x cross section of Earth (πR2)  0.0038 x 1.29 10 8 km2  510 5 Km2 Assumin a sheet of 0.1 mm thickness would have a volume of 510 7 m3 Stratospheric Particle Injection – Inspired by Volcanic Eruptions 49 More IR Flux IR Downward IR Cooling IR emission Less IR Flux IR Upward emission

IR G

Heating N

I L clouds Effects

on cirrus on absorption (IR)

I SolarFlux LessTotal

H Flux

Diffuse

E Enhanced N SolarFlux More Reflected More Clouds Flux SolarHeating Direct backscatter Reduced Indirect Indirect Effects on 4 3 weeks) 3 SO Less - 2 Solar Heating Solar 1 H    (nearIR) 2 absorption Ash forwardscatter SO depletion 3 O Tropospheric aerosols Tropospheric (Lifetime Heterogeneous Stratospheric Aerosol Sulfate from presentation a by 2010 Heidelberg Robock, Alan 2 O 2 CO H

3 years) 3

- t n

1 e c



2 e i

H u

e Q

 i s

S o

2 p

Stratospheric aerosols Stratospheric H SO

(Lifetime E Mount Pinatubo (1) Eruption June 1991

before

after

Photo: NASA Mount Pinatubo (2)

WMO (2003)

NASA Mount Pinatubo (3) Reflection

Effects of Mount Pinatubo, Philipines volcanic eruption (June 1991) on the radiation balance and on the hydrological cycle as an analog of geoengineering Trenberth and Dai (2007) Geophys. Res. Lett. Surface

from a presentation by Alan Robock, Heidelberg 2010 52 Optimal Particle Size?

Small Particles  More Surface/Mass (less mass needed)  But at size parameter x < 1 rapidly decreasing scattering efficiency  But more scattering in backward direction  also: particles settle less rapidly  However, the useful lifetime of particles is also limited by the stratospheric circulation

1 large particle,  8 small particles, radius r/2, same total volume radius r but twice the total surface area Why Endanger Particles the Ozone Layer? (1)

Katalytic Ozone destruction :

X + O 3  XO + O 2

XO + O  X + O 2

net: O + O 3  2O 2

X/XO: „Katalyst“

(e.g. OH/HO 2, NO/NO 2, Cl/ClO, Br/BrO)

HO X (Bates and Nicolet, 1950) NO X (Crutzen, 1970) ClO X (Stolarski and Cicerone, 1974; Molina and Rowland, 1974)

Katalytic ozone destruction explains difference between measured (lower) and

calcualted (ca. 3x higher) O 3 – concentrations and their dependence on.

Particles? How could Particle Sedimentation be prevented?

Prinziple of the „Light-Mill“ Black (Lichtmühle)?  warm Reflecting  cold

Radiation- source

Wrong explanation 1: Radiation pressure, Photons have momentum (p=E/c) but it is too small: solar radiation: 10 -4 W/cm 2  3·10 14 Photons/s, Momentum of a photon 10 -27 kgm/s  Force 3·10 -13 Newtons (for 1 cm 2) Moreover: Momentum transfer to black surface: p, reflecting surface: 2p  wrong rotational direction Wrong explanation 2 (Wikipedia): Warm layer of air at black surface provides larger pressure ... Enhanced Cloud Reflectivity due to Ship Traffic

low altitude Stratocumulus- clouds cover about 30% of the sea surface

A 2% enhancement of their albedo would provide a radiative forcing of -4 W/m². (Latham 2002) Cloud Whitening Scheme by John Latham (University of Manchester, NCAR) and Steve Salter (University of Edinburgh) to increasing cloud albedo by injecting more sea salt cloud condensation nuclei into marine stratus clouds. more condensation nuclei  same amount of condensing water produces more (and smaller) cloud droplets  more surface area  more scattering  higher cloud albedo  Cools Earth

from a presentation by Alan Robock, Heidelberg 2010 57 Primary Susceptible Regions for Cloud Whitening

Jones et al. 2009 Problem: Side-Effects regarding the Spatial and Temporal Distribution of Climate Forcing

Spatial and temporal distribution of forcing caused

by x4 CO 2

(negative) Radiation forcing due to stratospheric aerosol

Govindasamy et. al. Global and Planetary Change 37 (2003) 157–168 Consequences of CE Offseting 2xCO2 on the Global Temperature Distribution

Govindasamy et. al. Global and Planetary Change 37 (2003) 157–168 Consequences of CE on Global Precipitation Patterns

CE-measures offsetting the mean global temperature rise

caused by 2xCO 2

Change in daily precipitation column, (mm), J. Feichter et al. submitted

Blackstock et al. 2009 Ocean (Iron) Fertilization: Enhance CO2- Uptake Redfield Ratio: C:N:P:Fe 106:16:1:0.001 (e.g. Sarmiento&Gruber 2006) C  6.6 N C 1 P C 105 Fe CO2 – Uptake in the Ocean: The “Biological Pump”

S.W. Chisholm, Nature 407 , (2000) CO 2 Sequestration by Fertilization of Suitable Ocean Areas

Side Effects: … it is difficult to see how ocean iron fertilization with

enhanced production of such a low Csequestered : Fe added greenhouse gases like DMS, export efficiency would easily COS, organic halogen species scale up to solve our larger global C imbalance problems… M. Lawrence, Science, 2001 It would scale up to a region of 10 9 km²—more than an order of magnitude larger than the entire area of the Southern Ocean.

K. O. Buesseler et al., Science 2002 and 2008

Boyd, 2007 CO2 – Removal from the Atmosphere

“Synthetic Tree”

Art: Stonehaven CCS, Montreal, from Klaus Lackner , Columbia University Unconventional CE-Techniques

Climate Engineering is based on innovative technology „Immaterial“ transport of Sulfur to the stratosphere Bubbles in the ocean: Bright water Terramobile – LASER: Make Aerosol out of Air

And more ... Enhancing the Natural Sulfur Cycle to Slow Global Warming?

Wingenter O.W., Elliot S.M., Blake D.R. (2007), New Directions, Atmospheric Environment, 41 (34), 7373-7375, ISSN: 13522310, +Atmos. Env. 2008, 42, (19), 4806-4809, ISSN: 13522310.

The Idea: Iron-fertilize about 5% of the southern ocean area (1nM, 3 x per week) (don‘t care about C-fixation)  Enhance dimethyl-slufide (DMS) concentration by 20%  Enhanced DMS leads to +10% CCN (since ½ of CCN are due to DMS-oxidation)  ≈0.8% albedo increase due to „cloud whitening“ (from 46.0% to 46.4%)  Negative forcing of 3 W/m 2 (summer)

See also: „The Iron CLAW“ (M. Harvey, Environmental Chemistry 4 (6), 396- 399, 2007) Conclusions (Unconventional Techniques)

• There are many new ideas to facilitate CE • Some of them may actually work • It is likely that more ideas will emerge ...  We should not prematurely settle with the presently discussed techniques • In fact it could be that – should CE measures ever be implemented – none of the presently discussed techniques are actually used Efficiency – Cost – Safety - Timeliness of CE-Measures

source: Geoengineering the climate: Science, Governance and Uncertainty, The Royal Society, 2009 What Happens if we stop Climate Engineering Measures?

Robock et al. JGR 2008 How to Test Climate Engineering Measures?

The Role of Field Trials

Sooner or later, the improvement of our understanding of CE technologies will necessitate large-scale field trials that come very close to an actual application of the technologies. Such field trials should be accompanied by comprehensive monitoring programs. Even if we assume the best possible design for large-scale trials, unequivocal identification and quantification of the effects and side-effects of particular technologies would take many years or even decades. In the course of a field trial extending over such a long period, apparent effects and side-effects unrelated to the application of the technology would also occur.

The conduct of such a large-scale trial without the occurrence of significant social and political impacts must be considered one of the major challenges of climate engineering. Questions beyound Technological Feasibility and Cost of CE-Measures

CE in cases of severe emegency (Crutzen)? CE could give a feeling of false scurity (we continue as usual, apply CE if there should be a problem) CE could be used as excuse for neglecting mitigation and adapatation? Some CE-measures appear to be very cheap in comparison to mitigation  Danger of unilateral application? Ethics of CE? Legal questions (precautionary principle, compensation for damages) Political enforceability? Who decides on termination or continuation of CE – measuresin case of problems? Who can guarantee the continuation of CE-measures over centuries (or millennia)? What happens if CE-measures are (or have to be) terminated? Marsilius Projekt der Univ. Heidelberg: „The Global Governance of Climate Engineering“ RNZ v. 1.12.2009

Teilprojekte (Work Packages)

A: Umweltphysik: Profs. Leisner, Platt, Aeschbach, S. Müller-Klieser B: Philosophie: Prof. M. Gessmann, H. Fernow C: Humangeographie: Prof. H. Gebhardt, T. Wiertz D: Umwelt-Ökonomie: Prof. T. Goeschl, D. Heyen E: Psychologie: Prof. J. Funke, S. Wüstenberg F: Internat. öffentl.Recht: Prof. R. Wolfrum, D. Reichwein G: Politische Wissenschaft: Prof. S. Harnisch, S. Uther H: Politische Ökonomie: Prof. S. Walter, W. Dietz Really Roughly Estimated Cost of CE-measures (10 9 US$ per W/m2)

Reduction of CO2 Emission: 200 (for comparison) Urban albedo reduction: 2000 Desert albedo reduction: 1000 Cloud Whitening: 0.135 (or more) Stratospheric S-Aerosol: 2-67 Space Shades: 1700 (L1)

Source: Rickels et al. 2011 (BMBF-Report) Summary

• Climate modification measures are already being applied to our planet (Emission of greenhouse gases, deforestation, etc.) – although not deliberate. • The idea to add deliberate Climate Engineering to these measures may appear blasphemic, however there might be emergency situations where CE may be the only solution (e.g. because of time scales). • CE might not be feasible at all or much more difficult (and expensive) to implement than anticipated. • There are great dangers associated with CE: - Moral dangers – less incentive for mitigation („Climate Sceptics“: „Climate change is not a problem and CE is the solution“) - Side effects and unwanted effects - Political disturbances • However, research can answer some of these questions and reduce some of the uncertainties. “ T i m e M a g a z i n 2 4 . 3 . 2 0 0 8