The evidence and causes of climate change, the role of feedbacks linking the water and carbon cycles, the projected physical and human consequences for places, and the mitigation and adaptation strategies needed for a sustainable future.

What this dot point is asking

Edexcel wants you to explain the evidence and causes of climate change, explain the feedbacks linking the water and carbon cycles, analyse the projected physical and human consequences for places, and evaluate the mitigation and adaptation strategies needed for a sustainable future.

Evidence and causes of climate change

Natural factors (solar variation, volcanic activity, orbital Milankovitch cycles) shape long-term climate but cannot explain the rapid recent warming. The Keeling Curve at Mauna Loa shows atmospheric carbon dioxide rising from around $315$ ppm in 1958 to over $420$ ppm today, and global mean temperature has risen roughly $1.1\,^{\circ}\text{C}$ above pre-industrial levels, with the warmest years on record all falling since 2015.

Feedbacks linking the cycles

The Arctic is the clearest located case of feedback. Arctic sea-ice extent has fallen by over 40 per cent in summer since 1979, and as bright ice (albedo near $0.8$) is replaced by dark ocean (albedo near $0.06$) more solar energy is absorbed, accelerating warming, which is why the Arctic is heating around three to four times faster than the global average. Thawing Siberian permafrost is releasing stored methane, a feedback that could push the system past a tipping point.

Projected consequences for places

Consequences include sea-level rise threatening low-lying coasts and small island states (the Maldives, with a mean elevation near $1.5$ m, and Tuvalu, which has discussed relocation), shifting precipitation and drought, more frequent extreme weather, ecosystem stress and ocean acidification, and threats to food and water security. Impacts are uneven: the poorest and most exposed places, which contributed least to emissions, are often most vulnerable, a core equity argument.

Mitigation and adaptation

Mitigation reduces emissions through renewables, nuclear, energy efficiency, afforestation, carbon capture and storage and international agreements such as the Paris Agreement (2015, aiming to hold warming "well below" $2\,^{\circ}\text{C}$ and pursue $1.5\,^{\circ}\text{C}$) and carbon trading (the EU Emissions Trading System). Adaptation manages unavoidable impacts through flood defences, managed retreat, drought-resistant crops and water conservation. A sustainable future requires both, with equity between rich high-emitters and poor, vulnerable nations. Synoptically, players (high-emitting superpowers, vulnerable small states, NGOs) hold sharply different attitudes, and the futures of exposed places depend on global cooperation that is hard to secure.

Examples in context

Example 1: the Maldives. A low-lying Indian Ocean nation of around 1,200 islands averaging just $1.5$ m above sea level, the Maldives faces existential threat from sea-level rise. It has invested in adaptation (the raised artificial island of Hulhumale, sea walls around Male) and used diplomacy (a symbolic underwater cabinet meeting in 2009) to press high-emitting states for mitigation, illustrating the equity gap between those causing and those suffering warming.

Example 2: the Netherlands and the Delta Works. A wealthy, low-lying country where around a quarter of the land is below sea level, the Netherlands has pursued large-scale adaptation through the Delta Works storm-surge barriers and "Room for the River" managed-retreat schemes. It shows that effective adaptation is possible but capital-intensive, underlining why poorer, equally exposed places struggle to protect themselves and why mitigation remains essential.

Try this

Q1. Explain how the ice-albedo effect acts as a positive feedback. [4 marks]

• Cue. Warming melts reflective ice, exposing darker land or ocean that absorbs more heat, causing further warming and more melting.

Q2. Distinguish between mitigation and adaptation. [2 marks]

• Cue. Mitigation reduces emissions to tackle the cause; adaptation adjusts to cope with the consequences of warming.