L8 Flashcards
What does the IPCC say aboout negative emissions tech?
“the deployment of carbon dioxide removal to counterbalance hard-to-abate residual emissions is unavoidable if net zero Co2 or GHG emissions are to be achieved.”
to stay below 2oc given the amount of carbon already in the atmosphere we will require negative emissions tech to manage the emissions curve in time
What is the best estimate for mitigation and negative emissions per year to limit warming to 2oc
.5-3 Gt per year
What are four NETS?
- direct air capture
-bioenergy with carbon capture and storage
-enhanced weathering
-nature-based climate solutions
Whare are the 4 global resevoirs of carbon?
Atmosphere
land
ocean
geological
What is the broad theoretical underpinning of a NETS?
if we trap carbon and send it back it is not a NET as it is only addressed emissions going forward rather than previous emissions
if it cannot address past emissions it is not an NET
How does direct air capture work?
Takes carbon from the atmosphere and puts it into the geological reserve
filters the air to capture CO2 but requires a lot of air to capture a meaningful amount of CO2
What are the pros and cons of DAC?
low land footprint
high energy requirments –> to regenerate the absorbant requires electricity
high costs - tech might work but too expensive to be supported by the market?
Can DAC be scaled up in time?
We are currently at .001% capacity - fairly advanced development but difficult to model the tech diffusion
risks associated with assuming DAC can be deployed at scale - potential for a global temperature overshoot of .8oc
How does bionergy with carbon capture and storage work? BECCS
Carbon from the atmosphere goes into land (plants) - burn plants for energy and at that point of burning capture the carbon and put in the geological reservoir
this is negative emissions because the plants sequester carbon first and the carbon is captured from the burning
What are the pros and cons of BECCS?
Pros
generates electricity
modest costs
Cons
High land footprint
biodiversity cost is potentially huge - habitat loss is major threat to biodviersity
Is BECCS scalable?
we would need to scale 3x to provide sufficient Co2 capture and prevent warnings
but more emissions associated with bioenergy as you increase production because…
- conversion of habitats to provide bioenergy
- carbon cost of chopping down a forest outweigh the benefits we get from bioenergy
What are the give major threats to biodiversity?
Habitat degradation
pollution
exploitation
climate change
invasive species and disease
How does rock enhanced rock weathering work?
Atmospheric carbon reacts with minerals transferring carbon into geological reserves
silicate rocks applied to a field participate in this reaction
What are the pros and cons of enhanced weathering?
Pro
low land fooprint
moderate energy requirements
moderate costs
can be applied on any land
the most Co2 removal comes from the fertilisation effect on tress
most of the earths crust is silicate rocks - no geographical constraints
Cons
Co2 is emitted in moving rocks around and grinding them into a powder
changes the soil chemistry and could increase soil C emissions - unknown consequences on the soil and the stream water systems
What reaction does enhanced weathering rely on?
The Urey equation
silicate rocks react with Co2 to produce a bicarbonite ion - transported by ground or river water into the ocean – biological participated into bioorganisms shells at the bottom of the ocean = counter ocean acidification
- but this reaction takes place over millions of years
What is the potential impact on emissions pathways without NETS?
inability to scale NETS could lead to a substantial overshoot of 2o targets
difficult to model and understand as they are all in varying levels of development and have different land, energy and cost requirements
How does reforestation and natural capital work in the wider reservoir picture?
atmospheric co2 is taken up by plants and stored in the land
What are the pros and cons of nature based negative emissions?
Pros
- no energy requirements
- low cost
- potential benefits for biodiversity
- it is already happening - land is a huge Co2 sink
Cons
- high land footprint
How are nature based solution defined by the Un environmental assembly?
actions to protect, conserve, restore, sutainably use and manage natural or modified terrestrial, freshwater, coastal and marine ecosystems, which address social, economic and environmental challenges effectively and adaptively, while simultaneously providing human well-being, ecosystem services and resilience and biodiversity benefits”
What is the difference between natural climate outions and nature- based solutions
NCS - mainpulate natural ecosystems to address climate change = natural climate solutions use nature to MITIGATE climate change
NbS - solution to any environmental problem not just climate
e.g. plant trees around rivers to reduce pollutants to oceans
may deliver climate adaptation e.g. mangroves for coastal defence
What are the most effective natural climate solutions?
Reforestation
Avoided forest conversion
natural forest management
What are the co-benefits of nature-based solutions?
Human well-being
biodiveristy benefits
How do you measure forest growth?
Measuring pools - where carbon resides eg. trees
- reflects outcome of many underlying processes such s growth and mortality
but ignores soil C fluxes that determine C balance of whole ecosystem
i.e. doesn’t give the full picture
Measuring Fluxes
- the ACC movement of carbon between the ecosystem and the atmosphere
- cannot directly measure plant c uptake
-soil and plant c losses lumped together
but
we don’t understand the underlying processes of whether photosyn or respir. changed
What is the difference between old and young trees in terms of carbon dioxide removal?
Old trees are bigger and grow slower
Young trees are fast but smaller - takes them a while to catch up with the amoundont take up as much carbon as old
What is the impact of distrubing ecosystems
Ecosystems already hold a lot of emission inside of them - if we disturb them carbon is released
carbon in trees and soil - recovery of carbon in the soil and biomass
recovery can be v sow there is irrecoverable carbon
How many Gt of carbon will be irrecoverable by 2050 and why?
260 Gt of carbon
distrubrance to tropical peatlands and mangtroves as well as many forests
Aside from existing tree canopy how much extra canopy cover is possible and how many gt of carbon can it store?
.9 billion hectares of canopy cover
205 gt of carbon that would naturally support woodlands
however there is uncertainty in what constraints in our capacity to reach this potential - eg. how fast forests can grow and what about the land use for agriculture
What are the constraints on Co2 removal via reforestation and afforestation
- natural rate of carbon uptake by forests
- availability of suitable land - ecological constraints and economic and political constraints
- participation of people
regrowing a forest can take up a lot of Co2 but there is limited room for new forests
What are the pitfalls of forestry anywhere?
There are certain climates that are more effective for reforestation and afforestationie. not the tundra - unknown consequences of changing the colour of the land for instance
trees are a people-centred approach - tree or food producing plant, also need to be able to tend to the tree
