Week 5 Quiz Flashcards

Front: What is the main cause of increasing CO2 emissions?
Back: Anthropogenic (human) activities, including population growth and increased demand for material goods, energy, and services.

Front: By how much has atmospheric CO2 increased in the last 250 years?
Back: Atmospheric CO2 has increased by at least 140 ppm, from about 280 ppm in the pre-industrial era to approximately 424 ppm in 2024.

Front: How has the rate of CO2 increase changed over time?
Back: The first 50 ppm increase above pre-industrial levels took over 200 years (before the 1970s), but the next 50 ppm increase occurred in only 30 years.

Front: How do scientists determine past atmospheric CO2 levels?
Back: By extracting gas from tiny air bubbles trapped in ice cores from Greenland and Antarctica, which record past atmospheric composition.

Front: What was the atmospheric CO2 concentration before industrialization?
Back: About 270-280 ppm before 1750 AD.

Front: What is the Keeling Curve?
Back: A graph that shows the rise in atmospheric CO2 concentrations since the 1950s through direct air measurements.

Front: What is the dominant source of anthropogenic CO2 emissions?
Back: Fossil fuel combustion, which provides the main global energy source.

Front: Which sector is the largest contributor to greenhouse gas emissions?
Back: Electricity and Heat Production (25% of total emissions), closely followed by Agriculture, Forestry, and Land Use (24%).

Front: What percentage of total GHG emissions is carbon dioxide responsible for?
Back: About 75% (65% from fossil fuels + 11% from land use changes).

Front: How do methane (CH4) and nitrous oxide (N2O) compare to CO2 as greenhouse gases?
Back: Methane is more potent than CO2 but breaks down in about a decade. Nitrous oxide is also a strong GHG but is present in lower concentrations.

Front: How does methane (CH4) compare to CO2 as a greenhouse gas?
Back: Methane is much more powerful per molecule than CO2 but has a lower overall warming effect due to its lower atmospheric concentration (ppb vs. ppm).

Front: Why is methane’s atmospheric concentration lower than CO2?
Back: Methane has a short atmospheric lifetime (~10 years) before oxidizing to CO2, while CO2 remains for 200–1,000 years.

Front: How have methane concentrations changed since the pre-industrial era?
Back: Methane has increased from ~720 ppb to ~1950 ppb, about 2.5 times higher.

Front: What was the methane concentration during glacial times (~20,000 years ago)?
Back: About 400 ppb, compared to 720 ppb in interglacial times (pre-industrial era).

Front: How do scientists measure past methane concentrations?
Back: By analyzing tiny air bubbles trapped in ice cores, similar to CO2 measurements.

Front: What is significant about current atmospheric methane levels?
Back: They are the highest in the past 800,000 years and have been increasing steeply in recent years.

Front: What are some major sources of methane emissions?
Back: Wetlands, rice agriculture, biomass burning, ruminant animals, fossil fuel mining, and leaks in gas pipelines.

Front: How might climate change affect methane emissions?
Back: A 2°C temperature rise could increase methane emissions by 19%, partly due to permafrost thawing, which releases stored methane.

Front: What is the methane-climate change positive feedback loop?
Back: More methane emissions cause warming, which then leads to more methane release (e.g., from permafrost), further enhancing warming.

Front: Why do methane emissions from living plants pose a challenge for climate models?
Back: This newly discovered source complicates predictions, as greenhouse gas inputs to models must be well understood.

Front: What temperature increase limit has the IPCC set to prevent dramatic climate change?
Back: The global average temperature should not rise much above 2°C.

Front: By how much must global greenhouse gas emissions be reduced to stay within the 2°C limit?
Back: By 50-80% by the year 2050.

Front: Why is reducing CO2 emissions quickly challenging?
Back: While energy efficiency and renewable energy can help, they are unlikely to scale up fast enough to meet the IPCC reduction target.

Front: What is Carbon Capture and Sequestration (CCS)?
Back: A technology that captures CO2 from fossil fuel combustion, transports it, and stores it underground or in marine environments.

Front: Why is CCS considered an important interim solution?
Back: It allows fossil fuel use to continue while renewable energy infrastructure develops, reducing CO2 emissions in the meantime.

Front: For which CO2 sources is CCS most practical?
Back: Large stationary sources like power stations, refineries, and cement factories.

Front: Why is CCS not feasible for transportation emissions?
Back: Mobile sources like cars, planes, and trucks cannot easily use CCS technology.

Front: How can electrification of transport help reduce CO2 emissions?
Back: Electric vehicles can run on renewable energy or electricity from power plants with CCS.

Front: How might hydrogen fuel help in reducing transport emissions?
Back: Hydrogen produced from wind energy can serve as a clean fuel alternative for vehicles.

Front: What is the 'moral hazard' concern with CCS?
Back: The promise of CCS might reduce the urgency to transition away from fossil fuels, leading to continued dependence on them.

Front: What are the four main steps of Carbon Capture and Storage (CCS)?
Back: 1) Capture, 2) Transport, 3) Safe storage, 4) Continued monitoring.

Front: Why is continued monitoring important in CCS?
Back: To ensure stored CO2 remains contained and does not leak back into the atmosphere.

Front: At what stages of CCS can CO2 be lost to the atmosphere?
Back: Possible emissions and losses can occur during capture, transport, storage, and monitoring.

Front: Where is CO2 stored in CCS?
Back: In underground geological formations or marine environments.

Front: What will lectures on CCS include?
Back: Specific examples of operational CCS plants around the world.

Front: How much CO2 can CCS technologies capture from a power plant?
Back: CCS can capture 85-95% of carbon emissions from a power plant equipped with the system.

Front: Why does a power plant with CCS require more energy?
Back: CCS plants need 10-40% more energy than non-CCS plants, mainly for CO2 capture and compression.

Front: What is the net CO2 emission reduction from a power plant with CCS?
Back: Assuming secure storage, CCS reduces CO2 emissions by 80-90% compared to a plant without CCS.

Front: What is the difference between CO2 captured and CO2 avoided?
Back: - CO2 captured: The total amount of CO2 removed from emissions.

• CO2 avoided: The difference in net emissions between a plant with and without CCS.

Front: Why is CO2 avoided always less than CO2 captured?
Back: A CCS plant requires extra energy, which increases overall CO2 production before capture.

Front: What are the three types of carbon sequestration?
Back: 1) Geosequestration (underground geological storage)
2) Marine sequestration (storage in the ocean)
3) Mineral sequestration (chemical reactions with minerals)

Front: What is geosequestration?
Back: Geosequestration involves pumping CO2 deep underground for long-term storage in geological formations.

Front: Why are oil and gas reservoirs good locations for CO2 storage?
Back: These reservoirs are well-mapped, have existing infrastructure, and contain porous rock formations sealed by impermeable caprock.

Front: What is Enhanced Oil Recovery (EOR)?
Back: EOR involves injecting CO2 into an oil reservoir to reduce oil viscosity, making extraction easier. The CO2 can be recycled for further use.

Front: How does CO2 behave at depths below 800-1000 m?
Back: CO2 forms a supercritical fluid, behaving like a liquid, which allows it to flow and be stored efficiently.

Front: How can CO2 be stored in unusable coal seams?
Back: CO2 binds to organic matter in coal, displacing methane, which can then be used for energy production.

Front: Why do saline aquifers have the largest potential for CO2 storage?
Back: Saline aquifers are abundant, contain non-drinkable water, and can dissolve CO2, trapping it underground.

Front: What are sedimentary basins, and why are they good for CCS?
Back: Sedimentary basins are depressions filled with layered sediments that create natural reservoirs and caprocks for CO2 storage.

Front: What is marine sequestration?
Back: Marine sequestration involves pumping CO2 into the deep ocean to increase the rate at which it is removed from the atmosphere.

Front: How much CO2 have the oceans absorbed from anthropogenic emissions in the past 200 years?
Back: The oceans have absorbed 500 Gt CO2 out of the 1300 Gt CO2 total anthropogenic emissions.

Front: What are two proposed methods for CO2 storage in the ocean?
Back:

1. Dispersal of CO2 by ships

2. Creation of CO2 lakes on the ocean floor at depths greater than 3 km.

Front: Why must CO2 lakes be stored at depths greater than 3 km?
Back: At depths >3 km, CO2 is denser than seawater, allowing it to form a stable lake on the ocean floor that slowly dissolves into surrounding seawater.

Front: What are the three major risks of marine sequestration?
Back:

1. Ocean acidification – CO2 dissolves in seawater, lowering pH and harming marine life.

2. Non-permanent storage – Ocean circulation can bring CO2 back to the surface, where it can be released.

3. Harm to marine life – CO2 lakes could create anoxic conditions, making areas uninhabitable.

Front: How does CO2 affect ocean pH?
Back: CO2 dissolves in seawater, forming carbonic acid, which lowers the pH and increases ocean acidity.

Front: Why is ocean acidification a concern for marine organisms?
Back: Acidification dissolves carbonate minerals, threatening organisms that build shells and skeletons from calcium carbonate (e.g., corals, mollusks).

Front: Why is marine sequestration not a permanent solution?
Back: Ocean circulation (e.g., thermohaline circulation) can bring deep-sequestered CO2 back to the surface, where it may re-enter the atmosphere.

Front: How does temperature affect CO2 solubility in water?
Back: Warmer water holds less dissolved CO2, meaning rising ocean temperatures could cause stored CO2 to be released.

Front: How long does it take for stored CO2 to return to the atmosphere due to ocean circulation?
Back: It takes hundreds to thousands of years, but CO2 will eventually be released, creating problems for future generations.

Front: What is mineral sequestration?
Back: Mineral sequestration accelerates natural weathering by reacting CO2 with metal oxides or hydroxides to form stable carbonate minerals, permanently storing CO2.

Front: What is the general chemical reaction for mineral sequestration?
Back:
MO + CO2 → MCO3 + heat
(M = metal, MO = metal oxide, MCO3 = metal carbonate)

Example: CaO + CO2 → CaCO3 + heat

Front: What are some examples of metal oxides used in mineral sequestration?
Back:

1. Calcium oxide (CaO)

2. Calcium hydroxide (Ca(OH)₂)

Front: What are the benefits of mineral sequestration?
Back:

1. Permanent CO2 storage – Converts CO2 into stable carbonate minerals.

2. Useful byproducts – Carbonates can be used in construction.

3. Heat generation – The reaction is exothermic, potentially providing energy for heating or power.

Front: What are the challenges of mineral sequestration?
Back:

1. High energy demand – Requires 60-180% more energy than non-CCS power plants.

2. Costly – Estimated at several hundred US dollars per ton of CO2 stored.

3. Complex processing – Involves extracting, purifying minerals, and capturing concentrated CO2.

Front: What is enhanced weathering?
Back: Enhanced weathering involves adding ground-up minerals (e.g. olivine, basalt, crushed concrete) to soils to react with CO2, converting it into bicarbonate ions that are transported to oceans.

Front: How does enhanced weathering help with ocean acidification?
Back: It increases the flow of bicarbonate ions to the ocean, which helps neutralize the acidity caused by atmospheric CO2.

Front: What is a key challenge of enhanced weathering?
Back: Monitoring, reporting, and verification (MRV) of CO2 storage is difficult.

Front: What is mineral carbonation?
Back: Mineral carbonation uses metal oxide-rich industrial waste (e.g. cement, steel production waste) to react with CO2 flue gas, forming solid carbonate minerals that permanently store carbon.