Flashcards · IB Diploma Programme Environmental Systems and Societies · Topic 6

Atmosphere and climate change flashcards

22 cards on Topic 6, subtopics 6.1 to 6.4. Pick a subtopic or study them all.

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What is the composition of dry air?: N₂ 78%, O₂ 21%, Ar 0.93%, CO₂ about 0.04%. CO₂ was about 280 ppm before industrialisation and is now above 420 ppm.
Troposphere versus stratosphere: Troposphere: surface to about 12 km on average; weather, almost all water vapour, most of the mass; temperature falls about 6.5 °C per km. Stratosphere: to about 50 km; contains the ozone layer; temperature rises with height because ozone absorbs UV.
What is albedo and how do you use it?: The fraction of incoming solar radiation a surface reflects (0 to 1); Earth's overall albedo is about 0.30. Absorbed = incoming × (1 − albedo). Example: 300 W m⁻² on snow of albedo 0.8 → 60 W m⁻² absorbed.
Natural versus enhanced greenhouse effect: Natural: naturally occurring greenhouse gases keep Earth's average near 15 °C instead of about −18 °C (about 33 °C of warming); it is essential. Enhanced: extra warming caused by human additions of greenhouse gases.
How do greenhouse gases warm the surface?: Short-wave radiation comes in from the Sun; some is reflected and the rest absorbed. The surface emits long-wave (infrared) radiation, which greenhouse gases absorb and re-emit, some back towards the surface. They do not absorb UV or "reflect heat".

What is global warming potential (GWP) and CO₂e?: GWP: warming from 1 t of a gas relative to 1 t of CO₂, usually over 100 years (CO₂ 1, CH₄ about 28, N₂O about 265). CO₂e = mass × GWP. Example: 4 t CH₄ × 28 = 112 t CO₂e.
Main human sources of CO₂, CH₄ and N₂O: CO₂: fossil fuels, deforestation, cement. CH₄: livestock, rice, landfill, fossil-fuel leaks. N₂O: fertilisers. Halocarbons: refrigerants and foams.
Give three positive feedbacks in climate change: Ice–albedo (melting ice exposes darker surfaces that absorb more energy); permafrost thaw releasing CH₄ and CO₂; more water vapour in warmer air; forest dieback and fire. Negative feedbacks include more plant growth and more low cloud.
What evidence shows rising greenhouse gases and temperatures?: Direct CO₂ measurements (rising trend with a seasonal wobble from Northern Hemisphere plants); air bubbles in ice cores; instrumental temperature records — about 1.1 °C warming by 2011–2020 above 1850–1900 (IPCC AR6).
Name five impacts of climate change: Sea-level rise (thermal expansion and land-ice melt); more extreme weather; species and biomes shifting poleward and uphill; coral bleaching and ocean acidification; changes to crop yields, water supply and disease vectors; displacement of people.
What is a tipping point in the climate system?: A threshold beyond which a system shifts to a new, hard-to-reverse state.

Mitigation versus adaptation: Mitigation reduces emissions or removes greenhouse gases (tackles the cause): renewables, reforestation, carbon capture, carbon tax. Adaptation reduces harm (tackles the effects): sea walls, drought-tolerant crops, early-warning systems, managed retreat.
Kyoto Protocol versus Paris Agreement: Kyoto (1997): binding targets for industrialised countries only. Paris (2015): keep warming well below 2 °C and pursue 1.5 °C, through nationally determined contributions (NDCs) reviewed every five years. Both sit under the UNFCCC (1992).
What is a carbon sink?: A store that takes in more carbon than it releases, such as forests, peat and oceans. Protecting and expanding sinks is a form of mitigation.
What is the main limitation of solar radiation management?: It reflects sunlight to cool the planet, so it treats a symptom: greenhouse gases stay high and ocean acidification is left untouched.
How do you evaluate a climate strategy?: Say whether it is mitigation or adaptation; give strengths (scale, speed, co-benefits) and limitations (cost, who pays, technology risk, side effects, equity); bring in a perspective (technocentric vs ecocentric, richer vs poorer countries); end with a conditional judgement.

How is stratospheric ozone formed and how does it absorb UV?: Formation: O₂ + UV → O + O, then O + O₂ → O₃. Absorption: O₃ + UV → O₂ + O.
How does chlorine destroy ozone?: UV releases Cl from CFCs. Cl + O₃ → ClO + O₂, then ClO + O → Cl + O₂. Chlorine is regenerated, so it acts as a catalyst: one atom can destroy many thousands of ozone molecules.
Why does the Antarctic ozone hole form in spring?: Polar stratospheric clouds form in the polar winter; chlorine is released from them when sunlight returns in spring (September–October). Below 220 Dobson units counts as an ozone hole.
Montreal Protocol and Kigali Amendment: Montreal Protocol (1987), following the Vienna Convention (1985): phased out ozone-depleting substances; ratified by every UN member state. Kigali Amendment (2016): phases down HFCs, the substitutes, because they are strong greenhouse gases.
Ozone depletion versus climate change: Different mechanisms: ozone absorbs UV; greenhouse gases absorb infrared. The ozone hole does not cause warming and CO₂ does not destroy ozone. The link: CFCs and HFCs are also greenhouse gases.
Why is ozone recovery slow?: Ozone-depleting substances last decades in the atmosphere, so recovery lags behind the ban. The 2022 WMO/UNEP assessment expects the Antarctic ozone layer to return to 1980 levels around the 2060s.