Week 2 p 2 Flashcards
What is a well-mixed GHG?
A well-mixed GHG remains in the atmosphere a long time and a single value can describe the concentration well (i.e. CO2)
What is a short-lived GHG?
A short-lived GHG is a powerful climate forcer with a short time spent in the atmosphere (i.e. methane, sulphur, soot which leads to contrails..)
Why does shipping tend to initially lead to a reduced temperature effect?
Shipping fuel oil contains sulphur which cools initially before the effects of the CO2 lead to a small temperature increase after 30 years
Why does aviation tend to have a quicker fall in temperature impact over the years compared with road use?
Aviation fuel contains a mix of CO2 and non CO2 greenhouse gas products and so the impact of the CO2 on temperature is lesser
What is the global warming potential for CO2 compared with sulphur and NOX?
GWP for CO2 is consistently 1 for 20 or 100 years
GWP for sulphur and NOX is negative and becomes smaller as time progresses due to the products being more short-lived
How are aviation contrails formed?
- Atmospheric conditions are favourable (super-saturated w.r.t. ice)
- Aircraft engine particle emissions (soot) provide a nucleation site for
condensation and ice particle formation
How do contrails impact earth’s temperature at day and night?
During the day they can reflect sunlight back into space
(increase Earth’s albedo) – cooling effect
At night, they can trap outgoing long wave radiation –
warming effect
What can contrails become?
Contrails can develop into clouds, this is called aviation
induced cloudiness or contrail cirrus
How can activity impact GHG emissions and lead to reductions?
Mode shifting - move to public transport and reduce vkm
Active travel - walking and cycling
Change land use to reduce derived transport demand
Freight: * Reducing empty trailers on return from delivery
* Optimising delivery routes
* Larger vehicles
How can changes in energy intensity (kWh/km) reduce GHG emissions?
Short-distance travel has lots of stopping and starting with energy going into acceleration -> lighter vehicle load, regenerative braking (saves energy mostly from inertia = ma), and slow driving
Long distance travel has energy into overcoming drag -> move slower, reduce drag
Energy-conversion chain - more efficient for EVs than ICEs (internal combustion engines), although both are becoming more efficient with time
What are 6 principles for efficiency?
- Reduce the frontal area per person
- Reduce the vehicle’s weight per person
- When travelling, go at a steady speed and avoid using brakes
- Travel more slowly
- Make the energy chain more efficient
- (Travel less)
What is the logic behind using biofuels?
- Biofuels have the potential to reduce transport CO2
emissions. In theory, the CO2 emitted when the fuel is
burned was absorbed when the plant was growing - Bioethanol
- Biodiesel
- Biomethane
What is life cycle analysis?
Life cycle analysis (LCA) accounts for all of the energy and
emissions that result from the fuel supply chain and end use
Life cycle -> resource extraction -> refining/distillation -> distribution/storage -> energy consumption
What is the sustainability criteria relevant to biofuels?
Sustainability criteria: Renewable fuel must deliver at least a 50% GHG saving and must not originate from land with high biodiversity value or carbon stock; also a cap on food-crop sources
What is a problem with biofuels?
Not currently utilised much in the UK despite targets
