Exercises: Climate change

Look at the greenhouse effect diagram. Explain what each numbered arrow (1, 2, and 3) represents, why the natural greenhouse effect is essential for life on Earth, and what the human-caused alteration of it consists of.

Name three greenhouse gases, state the main source of each, and indicate which contributes most to current warming and why.

Relate the carbon cycle to the increase in atmospheric $\text{CO}_2$ since the Industrial Revolution, naming the two human processes that contribute most to this increase.

Distinguish between weather and climate, and explain why a week of intense cold in winter does not contradict the global warming trend, drawing on the difference between an isolated data point and a long-term average.

Explain what the albedo of a surface is, which surfaces on Earth have a high albedo and which have a low one, and why the melting of Arctic sea ice reduces the planet's average albedo.

Name two pieces of evidence of climate change observed in Spain (the retreat of the Pyrenean glaciers, earlier flowering, more frequent heat waves, rising sea level on the coast) and explain what each one consists of.

Explain what carbon sequestration is and name two natural carbon sinks (forests, soils, oceans, peat bogs), indicating how they store carbon and for how long.

What is a heat wave and how is it defined meteorologically? Explain why, in a warmer climate, heat waves are expected to become more frequent, longer, and more intense even if the average temperature only rises by one or two degrees.

Describe two consequences of climate change already observable in the ecosystems of the Iberian Peninsula and explain the physical or biological mechanism that produces them.

Differentiate between mitigation and adaptation strategies for climate change and give two specific examples of each, indicating at what scale (local, national, or global) they are applied.

The concentration of atmospheric $\text{CO}_2$ has gone from around $280\ \text{ppm}$ in pre-industrial times to around $420\ \text{ppm}$ today. Calculate the percentage increase and discuss what would have happened to ecosystems if this increase had occurred over centuries instead of less than two.

Sea level rises for two main reasons: the thermal expansion of water as it warms and the input of water from glaciers and continental ice sheets. Explain both mechanisms and discuss, using Archimedes' principle, why the melting of floating sea ice barely contributes to the rise.

The average temperature of the Iberian Peninsula has already risen by more than $1.5\ \text{°C}$ since pre-industrial times. Explain what consequences this warming has for the snow cover of Spanish mountains and how it changes the flow regime of the rivers that rise in them (more water in winter, less in summer).

The IPCC works with emissions scenarios, from the very ambitious to the very high. Explain what a climate scenario is, why science cannot announce a single future temperature, and what role human decisions (energy, economy, demography) play in the range of outcomes.

Many countries have committed to "carbon neutrality" by 2050. Explain what reaching net zero emissions means, what role removals by sinks play in the balance, and why it does not mean stopping emitting altogether.

Salt marshes and Posidonia seagrass meadows store large amounts of carbon in their sediments ("blue carbon"). Explain why they are especially effective and long-lasting sinks, and discuss what happens to that carbon when a marsh is drained or a meadow is destroyed by anchoring and construction work.

Design a mitigation plan for your local area: choose three sectors (for example, energy, transportation, and carbon sinks) and justify, for each proposed action, how it reduces emissions or increases removals and what co-benefits it brings.

Imagine that global warming exceeds the $+1.5\ \text{°C}$ threshold, triggering accelerated processes in high northern latitudes.\na) Model the interaction between the summer melting of Arctic sea ice and the oceanic radiative balance using a cause-and-effect flow chart. Predict the impact of this loop on heat absorption by the water and on ice formation in subsequent winters.\nb) Thermokarst lakes form in peatlands and thawing permafrost soils. Reason under what biogeochemical conditions the decomposition of organic matter will predominantly release $\text{CH}_4$ instead of $\text{CO}_2$, and justify, based on the relative radiative forcing capacity of both gases, why this worsens short-term forcing.\nc) Based on both mechanisms, justify what a "tipping point" is and argue why, once crossed, the total cessation of anthropogenic emissions might not be sufficient to stop warming.

A ski resort at an altitude of $1800\ \text{m}$ in the Rocky Mountains has seen its average natural snow season reduced from 120 to 75 days over the last three decades. To sustain economic activity, the management company plans to build a $200\,000\ \text{m}^3$ water reservoir and install artificial snow guns to cover $80\ \%$ of the skiable area.\na) Justify why this technical solution can be considered an example of "maladaptation", analyzing its energy balance, its carbon footprint, and the impact on water availability for downstream river ecosystems.\nb) If the winter $0\ \text{°C}$ isotherm rises an additional $150\ \text{m}$ over the coming decades, evaluate the thermodynamic limits of technical snowmaking (wet-bulb temperature) and predict the medium-term viability of the resort.\nc) Design an alternative socioeconomic and ecological adaptation proposal for the valley that replaces snow monoculture, justifying how it diversifies employment and protects alpine biodiversity.

Analyze the following data from two countries ahead of an international climate summit:\n• Country A (developed country): Population: 40 million; cumulative historical emissions (1850-2020): $18\ \%$ of the global total; current per capita emissions: $12\ \text{t}$ of $\text{CO}_2$/year; GDP per capita: $\$42\,000$.\n• Country B (small island developing state): Population: 1 million; cumulative historical emissions: $<0.05\ \%$; current per capita emissions: $1.2\ \text{t}$ of $\text{CO}_2$/year; GDP per capita: $\$3\,000$; its territory suffers from aquifer salinization and irreversible coastal erosion due to sea level rise.\na) Apply the principle of "common but differentiated responsibilities and respective capabilities" to justify what specific financing and mitigation obligations Country A must assume regarding the Loss and Damage Fund for the benefit of Country B.\nb) Country A proposes setting an identical $40\ \%$ cut in emissions for all countries relative to their current levels by 2035. Evaluate the asymmetric impact of this proposal on Country B using climate justice and socioeconomic development criteria.\nc) Design an equitable criterion for sharing the mitigation effort that weights cumulative historical emissions, per capita emissions, and the Human Development Index, justifying why equity is an indispensable requirement for the effectiveness of climate agreements.