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Mikhail Budyko - 1974

proposed injecting sulfur dioxide in the stratosphere to cool the earth (like volcanoes).


Edward Teller and collaborators - early 1990s

proposed putting designer (nanotech) particles into the stratosphere to deflect sunlight.


1992 - The National Academy of Sciences issues a

detailed study on geoengineering options, including a cost-benefit analysis for each option.


2006 - Paul Crutzen (Nobel Prize winner for his work on the Ozone Hole) argues

that the scope and speed of climate changes due to increasing CO2 -- coupled with the lack of any progress on mitigation – requires sulfate aerosol geoengineering solution be seriously considered.


Why should we consider geoengineering?

- Many see little progress in mitigation efforts. This could be the only way we avoid serious harm.
- The potential for unanticipated climate catastrophes. what if the West Antarctic Ice Sheet started to collapse? Huge drought or lots of violent storms that are clearly linked to global warming.
- Could be a much cheaper solution than mitigation.
- Hard to rule out high climate sensitivities.


Uncertainty in Climate Sensitivity

High sensitivity climates are hard to rule out. Very high temperature changes (e.g., 8 C) are unlikely, but hard to rule out (on the other hand, small temperature changes like 1 C are essentially impossible).


Two Main Strategies of Geoengineering.

- Taking CO2 out of the atmosphere.
- “Solar radiation management”: blocking out the Sun
to cool the Earth back down. What most people are talking about when they refer to geoengineering.


Remove CO2 from the air – scrubbing CO2

This is different from, and less practical than, capturing it at the power plant, which we call carbon capture and sequestration.
- Many processes can do this, but very expensive & energy intensive. No realistic way to do this at a large scale.


Ocean Fertilization

Promote enhanced CO2 take-up by the ocean
through photosynthesis. Add trace metals (iron) where they are needed gives leverage.
- It’s not practical, because not enough carbon gets buried per unit of effort. Life in the ocean spins up, but only a small fraction of the carbon gets buried.


Promote enhanced CO2 take-up by

the land in soils or vegetation.


Ocean photosynthesis

- Life in the ocean buries some carbon in sediment – the
Biological Pump.
- In some places life is limited by trace metals (e.g. Iron) and we can add some to speed up life there.


Ocean Primary productivity very Seasonal

obviously more productive with photosynthetically active radiation from Sun.


Downsides of Photosynthesis by Fertilizing the Ocean

- Studies show after the phytoplankton bloom, most carbon goes right back into the atmosphere.
- Major disruption to the base of the marine food chain.
- Could cause harmful algal blooms.


Haida Salmon Restoration Corporation

Village of Old Masset funded a project to spread 100
tons of iron sulfate off the coast of BC, to boost biological productivity, enhance salmon and store
carbon. July 2012.


Terra preta

black earth” in Portuguese; in the Amazon basin has tons of old carbon in it. Created by humans between 450 BC and AD 950. Adding charcoal to soil can keep carbon there for thousands of years! Extremely high quality soil too.


Amazonian soils are usually

infertile due to leaching of nutrients. Terra Preta soils can self-maintain and even expand – amazing old technology.


Key elements of Terra preta

- Wood Charcoal – humans use of fire makes them a
keystone species? Early farmers created charcoal with low-temperatures with low oxygen – smothered fires – and used it as a soil amendment.
- Organic matter and nutrients.
- Micro-organisms and animals in the soil.



Burning biomass without oxygen (pyrolysis).
- Can be made in biomass synfuel plants (half the carbon goes into fuel, half into char).
- Can be made in biomass synfuel plants (half the carbon goes into fuel, half into char).
- Can be buried in the ground to sequester carbon. Also improves soil quality: nutrients, water holding quality,
buffering, Microorganisms.
- Could help developing countries slow deforestation, improve food security, provide renewable energy, & sequester carbon.


Taking CO2 out of the atmosphere at a large scale
with biochar may be possible

Currently projects are extremely small but all technology is there.
- This is a little mentioned, possibly very important element of solutions to global warming. Could cut CO2 levels by 8 ppm within 50 years? (Hansen).


Solar Radiation Management

goal: reduce shortwave radiation that gets to the surface. If the radiative forcing decrease from this equals the radiative forcing increase from CO2, the global temperature change should be close to zero.
-   Paint roofs white
- Stratospheric Aerosols or nano-particles
- Reflective mirrors in Space or on Earth
-  Enhancing cloud reflectivity
-  Land Surface management


Goal of geoengineering:

decrease energy in from the Sun to make energy balance happen (& stop warming).


Can Dimming the Skies Perfectly Cancel the effects of increasing CO2?

No! Solar radiation and greenhouse gases have
different effects. Greenhouse gases have a different signature than solar forcing. Greenhouse gases warm nights more: Geoengineering by Solar Radiation Management would cool days more.


Other Problems with Dimming the Skies

- Precipitation has a different sensitivity to solar vs
greenhouse gases. Geoengineering should dry out the climate more (solar radiation helps evaporate more water vapor from the surface).
- Effects on plant growth? they need sunlight.
- Ocean acidification would continue. Remember this just depends on atmospheric CO2 levels. Large effects on marine life would not be prevented.


Would have to continue dimming forever

If somehow we weren’t able to continue the scheme, Earth would experience very rapid warming.
- Estimates suggest 2-4 C warming within 10 years
- Even after emissions go to zero (i.e., once we run out of fossil fuels), we’ll have to continue to do this until CO2 returned to a safe level (1000 years?).


The basic strategy for dimming: Block enough sunlight to cancel radiative forcing due to increasing CO2

feasibility increases as list goes on:
- Solar reflectors placed in outer space at a point where the gravitational field from the earth cancels that from the sun.
- Mirrors orbiting the earth to reflect sunlight.
- Make more clouds or more reflective clouds.
- Place/shoot tiny particles in the stratosphere that reflect visible sunlight but don’t absorb infrared radiation.


Stratospheric Sulfur Injections

- Designed to imitate volcano eruptions
- Inject a sulfate aerosol precursor (such as sulfur dioxide SO2) into the stratosphere that then forms sulfuric acid solutions & eventually small particles.
- These aerosols increase earth’s albedo by reflecting solar radiation back to space.
- When injected really high up & if the particles remain small, they take a long time to fall out (months).
- Cheap compared to some estimates of mitigation costs, 10-20 billion $US/year.


Possible (unproven) options for getting 10Mt of sulfur aerosols in stratosphere each year

Artillery: shooting barrels of particles into stratosphere with 16” Iowa Class
naval guns
- Three guns firing twice per minute for 300 yrs
- Doable and affordable compared to mitigation of CO2 – in short term.
- “…surprisingly practical” (NAS 1992)


Some downsides of the stratospheric aerosol sunshade solution

- Large uncertainty to how much/how often you
have to inject sulfur into the stratosphere to cancel warming effect of increased CO2
- Not clear injecting SO2 works, recent study
suggests injecting sulfuric acid instead!
- Sulfur chemicals in the stratosphere may destroy
ozone in the protective ozone layer. So we might try nanoteched particles (may be difficult or impossible to remove).


Unintended Impacts of SRM

- May be able to offset global temperature rise but
since it’s not the same kind of forcing it’s impossible to cancel exactly.
- For example, these schemes alter precipitation
Stratospheric aerosols tend to dry the tropics
Sea spray-cloud brightening over ocean preferentially
cools the ocean, causing land-sea temperature gradients that tend to strengthen summer monsoons


Profound and unaddressed issues associated with geoengineering

- Who decides if it should be deployed, and at what level? Who decides if it should be stopped? What if one country decides to do it on its own, even though it harms another country?
- There are important cultural, legal, political, and economic implications of geoengineering. How will they be balanced?
- Moral hazard: If we have a possible solution to global warming, will we be less inclined to reduce carbon emissions?
- We can’t rule out unanticipated harmful and perhaps irreversible consequences (e.g., ozone hole).



- We have the technology and innovation (but not the
commitment of government incentives) to halt the increase emissions of CO2, reasonably fast and even reduce emissions greatly.
- Progress has been (still is) too slow to stem the tide however: Lack of public resolve and  lack of leadership and commitment in business and government.



- It is incredibly easy and (in the short term) inexpensive compared with reducing emissions and transitioning to a non-carbon emission economy. Cost is maybe only ~$10B/yr compared to ~$200B/yr to reduce carbon emissions (lots of uncertainty in these estimates though). Cost is less than 0.1% GDP for US, less than 2% for about 30 countries.
- Players who are currently influential and have a lot to lose if greenhouse gas emissions are limited/reduced (oil and gas companies, libertarians) don’t lose from climate engineering.
- Whoever holds the contract for the solution has huge profits guaranteed for a millennium.


NRC Recommendations – 2015

Mitigation preferred. Research CO2 Removal. Don’t Deploy Albedo Enhancement. Research Albedo Modification. Measure Climate Forcing Changes. Study the Governance of Climate Intervention Research.