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Geoengineering the atmosphere (Impacts of CDR (Causes reduction in atm CO2…
Geoengineering the atmosphere
Climate change
20th century
Extra-tropics warming more quickly than tropics
More complex patterns of regional change- annual precipitation over land has increased in regions but reduced (below 0mm) in others
Widespread warming-
land warming more quickly than oceans
21st century
what can be done
Mitigation
Human intervention to reduce the sources or enhance the sinks of greenhouse gases
Adaptation
The process of adjustment to actual or expected climate and its effects
Seeks to avoid harm or exploit beneficial opportunities
Global annual mean surface air temperatures have increased-
projections for each RCP are also expected to increase- some showing up to 6 degrees celsius temp surface temp change
Carbon dioxide removal
Intention is to reduce the atmospheric CO2 concentrations- causing a cooling effect
Set of techniques that aim to remove CO2
directly
from atm
By increasing the natural sinks of carbon
Vegetation stores carbon
Oceans act as reservoirs for carbon
Long term storage in sediments and land in Earth
By using chemical engineering to remove the CO2
CDR methods
Afforestaion and reforestation
Grow plants and trees and use them for bio-energy with carbon capture and storage
Biochar- wood turned into charcoal, buried/ planted within soils to lock carbon and fertilise soils
Ocean fertilisation and ocean upwelling
Geoengineering
A broad set of methods and technologies that aim to
deliberately alter the climate system
in order to alleviate the impacts of climate change
large scale
supplement to mitigation and adaptation- not an alternative
mitigation and adaptation may be too slow
Geoengineering is NOT: reducing emissions by CCS, biofuel energy production, reducing emissions from deforestation and degradation
Earth's energy budget
If Earth's climate system is in balance, these 3 factors will balance out to zero- there is no warming or cooling annually
Factors affecting radiation
Greenhouse gases
Increase in greenhouse gases affects the outgoing long wave radiation
Clouds
Affects the solar radiation that the system receives- low dense clouds are very good at reflecting solar radiation leading to a cooling impact
Clouds can have a warming impact at night as there is no solar radiation to be reflected by clouds still emit long wave radiation
Aerosols
Interact with clouds- gives growth to cloud droplets and can be strongly absorbing of solar radiation- warms mid levels of atm, cause cooling lower down
Surface albedo
Vegetated areas have low albedo so absorb most incoming radiation
Oceans absorb solar radiation- low albedo
Snow/ ice have high albedo- cause reflection of shortwave radiation
Radiation
Outgoing reflective solar radiation-
Proportion of incoming is reflected back to space- can be reflected by clouds or surface of Earth
Outgoing longwave radiation-
radiation emitted by the Earth, by clouds and molecules in the atmosphere
Incoming radiation from sun-
drives climate system
Incoming solar radiation is 340Wm-2, 102Wm-2 is scattered back to space-
30% incoming is scattered back to space
Impacts of CDR
Causes reduction in atm CO2 and temps
If CDR not persisted, eventually climate will return anyway-
temporary
Long time scale- slow to take effect
Risk of outgassing from oceans and terrestrial stores
Use of technology and deployment is uncertain
Unlikely to present option for rapidly preventing climate change
Feedbacks on other parts of energy budget (albedo)
Solar radiation management
Intentional modification of Earth's shortwave radiative budget with aims to reduce climate change
Albedo=
the fraction of solar radiation reflected by a surface or object
Estimated planetary albedo: SW radiation relfected (102)/ incoming (340)= 30%
SRM methods
Mirrors in space
Stratospheric aerosols
Delivery by aircraft, rockets, balloons, precursor gases
lifetime long in stratosphere
Marine cloud brightening
Injection of sea spray into boundary layer
Increased cloud albedo and increased scatter of SW radiation
Ocean, desert, crop and urban albedo enhancement
Impacts of SRM
(assuming all technologies happened in one go in 2020)
Temperature has rapid response to SRM
- reduction in global temperature in 10 year time frame
Change in temp reflects scale of geoengineering intervention
As soon as you stop SRM, climate system goes back to where it was beforehand-
temporary
For stratospheric aerosols: cooling effect is strongest over land than oceans
Feedback is magnifying climate change in Arctic
SRM reduces precipitation
- precipitation proportional to atm heating/ cooling rates