The evidence for and causes of past and present climate change; the greenhouse effect and feedbacks; the differential impacts on people and environments; and the mitigation and adaptation responses, evaluated synoptically across physical and human geography.

What this dot point is asking

This Geographical debate asks you to weigh the evidence for and causes of climate change, explain the greenhouse effect and feedbacks, evaluate the differential impacts on people and environments, and assess the mitigation and adaptation responses, all synoptically, drawing physical and human geography together. It is one of five debates from which you study two for Paper 03.

The answer

Evidence for past and present climate change

The evidence is multiple and convergent. Ice cores record temperature and atmospheric composition over hundreds of thousands of years, showing carbon dioxide and temperature cycling together between glacials and interglacials. Instrumental records show roughly $1.1$ degrees Celsius of warming since pre-industrial times, accelerating in recent decades. Physical indicators, retreating glaciers, shrinking Arctic sea ice, rising global sea level, earlier springs, corroborate the thermometers. The strength of the case lies in this convergence of independent lines, and in the recent departure from the natural pattern visible in the long record.

Causes: natural and anthropogenic

Climate changes through natural and human forcings. Natural drivers include Milankovitch cycles (orbital variations pacing the glacial-interglacial rhythm over tens of thousands of years), solar output variations, and volcanic eruptions (short-term cooling from aerosols). These explain past change and ongoing background variability. The dominant cause of present warming, however, is anthropogenic: the burning of fossil fuels and deforestation have raised atmospheric carbon dioxide from about $280$ to over $420$ ppm, plus rising methane and other greenhouse gases. The isotopic fingerprint of the added carbon, and the mismatch between natural forcings and the observed rapid warming, point firmly to human activity as the principal driver.

The greenhouse effect and feedbacks

The enhanced greenhouse effect drives the warming: added greenhouse gases trap more outgoing longwave radiation. The danger lies in feedbacks. Positive (amplifying) feedbacks dominate the concern, the ice-albedo feedback (melting bright ice exposes dark, absorbing surfaces), the permafrost-carbon feedback (thaw releases carbon dioxide and methane), the water-vapour feedback (warmer air holds more water vapour, itself a greenhouse gas), and reduced ocean solubility (warmer water absorbs less carbon dioxide). Negative (damping) feedbacks exist (enhanced plant growth, faster weathering) but act slowly. The net effect is a non-linear system that can amplify an initial warming and approach tipping points such as ice-sheet collapse or Amazon dieback, which is the key synoptic link across the course.

Differential impacts and responses

The impacts of climate change are uneven and inequitable. Physical impacts (sea-level rise, more intense extremes, shifting rainfall, ecosystem stress) translate into human impacts that fall hardest on low-lying, low-income and agriculturally dependent places, often those that contributed least to emissions. Small island states, the Sahel and deltaic regions are especially exposed. Responses split into mitigation (reducing emissions and enhancing sinks: renewables, efficiency, carbon pricing, the Paris Agreement) and adaptation (managing the consequences: flood defences, drought-resistant crops, managed retreat). Because some warming is locked in, both are needed; the recurring synoptic judgement is that mitigation sets the ceiling on how much adaptation will ultimately be required, and that equity must shape who pays and who is protected.

Examples in context

Example 1. Small island developing states (for example the Maldives and Tuvalu). Low-lying island states face existential threats from sea-level rise, storm surge and freshwater salinisation, yet contribute negligibly to global emissions, the clearest case of the inequity of climate impacts. They pursue adaptation (sea defences, raised infrastructure, even relocation planning) while pressing for global mitigation and climate finance at COP negotiations. They are the textbook example for the differential-impacts and equity strands and a powerful synoptic link to coastal landscapes and oceans.

Example 2. The Paris Agreement and the mitigation-governance challenge. The 2015 Paris Agreement commits nearly all states to limit warming to well below $2$ degrees, ideally $1.5$, through nationally determined contributions. It illustrates global mitigation governance: it sets a shared direction and ratchet mechanism, but its effectiveness depends on national follow-through, and current pledges fall short of the goal. This connects climate change to the carbon-cycle management strand and to the governance debates, and provides balanced evidence for the extended-response essay on responses.

Try this

Q1. Name two lines of evidence for present climate change. [2 marks]

• Cue. Any two of: instrumental temperature records, retreating glaciers and sea ice, rising sea level, ice-core data, earlier seasonal events.

Q2. Explain why the impacts of climate change are described as inequitable. [4 marks]

• Cue. The poorest, low-lying and agriculturally dependent places are most exposed and least able to adapt, yet have contributed least to greenhouse-gas emissions, so the burden falls hardest on those least responsible.