chapter 5 review questions

What are the three factors that matter for the predictive power of climate models?

1. understanding fundamental physics laws & atmospheric feedback mechanisms

2. accuracy of underlying socioeconomic assumptions that dictate future GHG emission trajectories

3. available computational processing power

How can we test if climate models are correct?

• hindcasting: run models back in time to see if they accurately replicate known data

• if yes, they can test future climates

Concept and empirical evidence of climate sensitivity.

• expected equilibrium increase of global average surface temp resulting from permanent doubling of atmospheric CO2 levels above pre-industrial levels

• current evidence & climate modelling: 2.5-4ºC

• climate system has powerful feedback loops that amplify initial GH warming

Why did the IPCC recently abandon the SSP5-8.5 "business as usual" trajectory?

• core assumption: global coal consumption could multiply by 2100 → not realistic baseline for BAU future

• implausible due to falling costs for renewable energy, shifts away from coal, & expanding global climate policies

Which emission path is likely under current NDCs, and what temperature increase does it imply?

• moderate emission path that sits below worst-case scenarios, but lacks rapid cuts needed for safe stabilisation

• implies that global emissions will plateau or slightly decline by 2030

• planet path toward 2.4-2.7ºC temp increase by 2100 → overshoots paris limits

What is natural carbon sequestration?

• long-term process when planetary ecosystems naturally absorb & store atmospheric CO2

• occurs through photosynthesis in terrestrial forests & wetlands, and physical/chemical dissolution into waters & oceans

Why does a 50% absorption by sinks not mean we only have to cut emissions by 50%? Give two counterarguments.

• 50% emission reduction = concentration gradient shifts → sinks slow absorption rate rather than maintaining absolute volume

• global temps rise → land & ocean sinks get climate-induced stress → weakens their long-term capacity to absorb carbon → need net-0 emissions to stabilise temps

How does global warming affect extreme weather frequency? Explain using a normal distribution.

• entire curve shifts right → higher mean

• far-right tail expands → extreme hot more frequent

• far-left tail shrinks → extreme cold less frequent

Explain two processes of sea-level rise, main drivers, future changes, and expected rise by 2100.

1. processes: thermal expansion of sea water as it traps heat, & physical melting of land-based glaciers & ice sheets

2. historic drivers: thermal expansion & mountain glaciers melting

3. current drivers: accelerating melt from greenland & arctic ice sheets

4. expected rise: 0.4-0.8

What are tipping points, and how do they affect the impact of global warming?

• critical thresholds where tiny temperature increase triggers a massive, unstoppable change in an ecosystem

• crossing it activates positive feedback loops that accelerates global warming

• once triggered, they become self-sustaining → will continue even with human emission reductions

Present two tipping elements, their mechanisms, certainty, and timeframes.

• amazon rainforest: climate-driven drought & deforestation disrupt internal moisture recycling loop → threaten to abruptly transition entire ecosystem into a dry savanna over decades

• greenland ice sheet: ongoing melting lowers ice sheet's surface altitude into warmer layers of lower atmosphere → initiates a self-reinforcing melting cycle that will lock in multi-meter sea-level rise over centuries

How likely are "abrupt" substantial changes within a couple of decades?

• risk of crossing individual regional tipping thresholds increases with every degree of warming

• scientific consensus: sudden, global-scale climate collapse occurring within a couple of decades remains low

• massive tipping systems will unfold over centuries rather than a few years

• initiation of these irreversible changes is a near-term risk if warming surpasses 1.5-2ºC

How is global warming shifting the distribution of diseases?

• it alters the geographic distribution of infectious diseases by expanding the warm, humid habitats required by climate-sensitive disease vectors eg mosquitoes & ticks

• as temperatures rise, they migrate into higher latitudes & loftier altitudes, exposing previously unexposed human populations to diseases like malaria, dengue fever, & Lyme disease

• warmer waters accelerate proliferation of waterborne pathogens eg cholera

Agricultural productivity: One positive and one negative example of global warming

• high-latitude regions: GW can temporarily boost agricultural productivity by lengthening frost-free growing season & enhancing photosynthesis via CO2 fertilisation

• low-latitude, arid regions: rising temperatures cause heat stress, accelerate topsoil moisture evaporation, & trigger prolonged droughts that collapse staple crop yields & devastate local food security

Give two examples of positive effects of global warming for humankind.

• Warmer winter temperatures in temperate zones reduce seasonal cold-related human mortality rates & lower the residential energy demand required for space heating

• retreat of Arctic sea ice opens up new, shorter international maritime shipping lanes & unlocks access to previously unreachable northern mineral & energy reserves

How will climate change damages be distributed, and which countries are most affected?

• highly unequally distributed → disproportionately harm developing nations located in tropical and subtropical zones

• these countries face the most severe physical impacts (intense heatwaves, agricultural failure) while lacking the financial resources, infrastructure, & institutional adaptive capacity to cope

• wealthier nations in temperate latitudes have more economic resilience & may experience temporary net benefits in certain sectors before higher warming levels set in

Provide two reasons why the transition to a zero-carbon economy is so difficult.

• modern global society is structurally anchored to using fossil-fuel power plants, factories, & transport networks that represent immense sunk capital costs & political resistance to change

• fossil fuels have high energy density & reliability that clean alternatives struggle to match in heavy industrial processes → deep decarbonisation is technically challenging & expensive

Will we achieve net-zero by 2050 based on current trends? If not, when?

• no

• unless international mitigation efforts, clean energy financing, & regulatory mandates are dramatically accelerated, current trends indicate 2070 or the final decades of the 2100s