Global atmospheric circulation and ocean currents redistribute heat; natural causes explain past climate change over the Quaternary, evidenced by ice cores, tree rings and historical sources.

What this dot point is asking

This is Edexcel GCSE Geography B (1GB0) Paper 1, Section A (Topic 1, Hazardous Earth). Edexcel expects you to explain how the global atmospheric circulation and ocean currents transfer and redistribute heat energy around the Earth, how that circulation fixes the location of arid (high-pressure) and high-rainfall (low-pressure) zones, and the natural causes of climate change. You must also know how scientists reconstruct past climate from ice cores, tree rings and historical sources across the Quaternary period and for the UK since Roman times. Questions are set in a resource context, often a climate graph, so data skills are tested alongside the theory.

Global atmospheric circulation

The Sun heats the Earth unevenly. The Equator receives concentrated, high-angle sunlight and a surplus of energy, while the poles receive low-angle sunlight spread over a larger area and a deficit. If nothing moved this heat, the tropics would keep warming and the poles keep cooling, so the atmosphere and oceans constantly transfer heat from the Equator towards the poles to keep the system in balance.

This is why the location of the world's climate zones is no accident. The wet tropical rainforests sit under the rising air of the Inter-Tropical Convergence Zone; the great deserts (the Sahara, the Arabian and Australian deserts) sit under the sinking air at around 30 degrees. Ocean currents add to this transfer: warm surface currents such as the North Atlantic Drift carry tropical heat polewards, which is why the UK is mild for its latitude, while cold currents return cooler water towards the Equator.

Natural causes of climate change

Climate has never been fixed. Long before humans, the Earth swung between cold glacial periods and warmer interglacial periods, and these natural changes have four main causes.

These operate on very different timescales: orbital cycles act over tens of thousands of years and drive the ice ages, whereas a volcanic eruption cools the climate for only a year or two. The current geological period, the Quaternary (the last 2.6 million years), has seen many of these glacial and interglacial swings.

Evidence for natural climate change

Because instrumental records only go back a couple of centuries, scientists reconstruct past climate from natural and human archives.

• Ice cores. Cores drilled from ice sheets in Antarctica and Greenland contain annual layers of ice with trapped air bubbles. The bubbles record past carbon dioxide concentration, and the ratio of oxygen isotopes in the ice records temperature, giving a year-by-year record stretching back hundreds of thousands of years.
• Tree rings (dendrochronology). Each year a tree adds a growth ring; wide rings indicate warm, wet years and narrow rings indicate cold, dry years, so counting and measuring rings reconstructs climate back thousands of years.
• Historical sources. Paintings, diaries, harvest and grape-harvest records, and records of fairs held on a frozen River Thames all evidence the colder "Little Ice Age" and reconstruct UK climate since Roman times.

Try this

Q1. Explain how sinking air at about 30 degrees north and south creates desert conditions. [4 marks]

• Cue. Air that rose at the Equator cools, loses its moisture and sinks at 30 degrees, warming and drying as it descends, creating high pressure with clear skies and very low rainfall.

Q2. Explain one way tree rings provide evidence of past climate change. [2 marks]

• Cue. Each year a tree adds a ring; wide rings show warm, wet years and narrow rings show cold, dry years, so the pattern reconstructs past climate.