L15 - Solutions

What is geoengineering?

• Large-scale deliberate manipulation of our climate to keep earth in a habitable state for humans

  • Carbon dioxide removal

  • Solar radiation management

How does afforestation/reforestation remove carbon dioxide?

• Reforestation = restoring trees

• Afforestation = growing trees where they were never before

• Global REDD (Reducing Emissions by Deforestation and Degradation) = wealthier countries pay poorer countries to not cut down trees

  • Supplements the profit they would have received from selling timber, etc.

How sustainable is reforestation/afforestation for carbon dioxide removal?

• Some debate over older trees and whether they are continuing to remove carbon from the atmosphere

• Once trees reach a certain level of maturity, they stop removing carbon from the atmosphere, but continue to store previously absorbed carbon.

What are the issues associated with reforestation/afforestation?

1. Need suitable soil to grow trees; this soil isn’t being used to grow food and food security is an increasing problem

2. Trees have a lower albedo (reflectivity) than whatever vegetation was growing there before, and can have a warming effect.

   • This is offset to a certain extent by transpiration.

   • In tropical regions, the evapotranspiration cooling effect will outweigh warming effect

   • In Boreal regions, the decreasing reflectivity dominates and planting trees can have a warming effect

3. Carbon is vulnerable - more frequent and intense forest fires are putting trees in more vulnerable positions

How could BECCS remove carbon dioxide?

• Bio Energy with Carbon Capture and Storage (BECCS) = growing biomass (fast-growing trees) are burned in a power plant and the released CO2 is captured and stored.

• An improvement on biofuels

How can biochar remove carbon dioxide from the atmosphere?

• Between 500BC and 1000AC, Amazonian natives produced charcoal to produce fairly pure carbon and then were burying it in the soils to boost soil fertility and productivity.

• Biochar introduces carbon particles into the soil which are able to hold onto nutrients and converts carbon to immovable version and is buried.

How will enhanced rock weathering remove carbon dioxide from the atmosphere?

• People try to take advantage of the geological carbon cycle - where magnesium and carbon silicate minerals weather.

• The powder from crushed rocks are buried and its minerals are dissolved in the soil, releasing silicon, which is taken up by plants and used to be able to cope with drought and resist insects and pathogens better.

• Nutrients run off into oceans; silicate favours growth of diatoms over red algal blooms.

  • By increasing silica relative to phosphorus, more diatoms = more biodiversity.

What is the environmental cost of enhanced rock weathering?

• Mining is needed to get this rock powder, which has environmental costs associated with it.

• Whilst there are large stockpiles of basalt that could be used, this could generate dust.

• There is also a need to ensure the rocks do not contain poisoning elements that could be transferred to the soil.

What is Direct Air Capture?

• Sucking CO2 from atmosphere and storing it somewhere

• Can be set up anywhere

  • On top of buildings

  • Uninhabited deserts

How could ocean fertilisation remove carbon dioxide from the atmosphere?

• By boosting productivity in oceans, there is more growth which could contain carbon.

• When these die, the carbon-containing organisms sink to the bottom where the carbon is left.

What are the risks associated with ocean fertilisation?

• Boosting biomass productivity in one area could cause nutrient deficit downstream

• Adding nitrogen and phosphorus to oceans could cause eutrophication.

How could ocean pumps remove CO2 from the atmosphere?

• The water at the ocean surface is at equilibrium with atmospheric CO2.

• By increasing the circulation rate of ocean water by pumping deeper waters containing low amounts of CO2 to the top, this could facilitate more carbon to be dissolved

Where and how could CO2 be stored?

Pressurise CO2 and concentrate it down, converting it to liquid and:

1. Pumping it into saline aquifers

2. Pumping it beneath ice caps where the liquid CO2 freezes into solid compounds

3. Pumped to deep sea depths where, due to its density, the CO2 will stay at ocean’s pressure and temperature.

4. Pump into basaltic rock. When the basaltic rock fractures, silicate minerals react with CO2 to form carbonates, where CO2 is locked up.

What is solar radiation management?

Aims to reduce the amount go energy the earth’s surface receives from the sun by reflecting back into space.

What is cloud albedo enhancement?

• The creation of clouds are promoted in the troposphere by spraying sea water into the atmosphere, increasing cloud condensation nuclei

• By enhancing cloudiness, the albedo is increased.

How can stratospheric aerosols be used?

• More regional effects in stratospheric aerosols

• Some sort of aerosol-generating deice which is floated in the atmosphere promotes cloud formation (sulphur dioxide and hydrogen sulphide)

How can space mirrors be used?

• By using finely disseminated aluminium particles that reflect light, the energy reaching the earth’s surface will be reduced

• Would have a global impact, possibly reducing seasonal contrast between poles and equator

What is the risk of solar radiation management?

• The Termination Effect

  • Strategies would have a rapid effect but would be short lived.

  • To maintain strategies, they would need to be maintained.

  • If you stopped renewing technologies, suddenly the amount of radiation and CO2 will increase rapidly.