IGCSE Geography / Fragile environments and climate change

Natural causes of climate change

Edexcel International GCSE Geography (4GE1), chapter 7: Fragile environments and climate change, specification point 7.1c. Free lesson.

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Natural climate change can be caused by Milankovitch cycles, changes in the Sun’s energy output and volcanic eruptions. These natural causes do not explain the Earth’s warming since the 1950s.

How Milankovitch cycles change climate

The Earth’s orbit changes slowly in three ways. These Milankovitch cycles alter how much of the Sun’s energy reaches different parts of the Earth. Together, they help start and end ice ages, which are long cold periods. Orbit shape: the path changes from nearly circular to more oval and back, over about 100,000 years. Tilt: the Earth’s axis leans more, then less, over about 41,000 years. Wobble: the axis slowly swings round like a spinning top, over about 26,000 years.

How solar variation affects climate

Solar variation means changes in the energy the Sun gives out. The number of sunspots, which are dark patches on the Sun’s surface, rises and falls over about 11 years. More sunspots mean the Sun gives out slightly more energy. For an exam answer, name sunspots or the Sun’s energy output. Saying only “changes in sunlight” is too vague.

How volcanic eruptions cool the Earth

Volcanism means volcanic activity. A large eruption can affect climate within months. Mount Pinatubo in the Philippines erupted in 1991, sending ash and sulfur dioxide high into the atmosphere. The sulfur dioxide formed a haze of tiny droplets that spread around the Earth. This haze reflected sunlight back towards space, so less energy reached the surface. The Earth cooled by about 0.5 °C for about two years. A large eruption cools the climate. The effect is temporary and is usually gone within a year or two.

Why natural causes do not explain warming since the 1950s

The Earth has warmed since the 1950s, but the natural causes do not fit this recent warming. Each has a different timescale or effect. Milankovitch cycles take tens of thousands of years, far too long to cause a change over a few decades. Solar variation follows an about 11-year cycle, but there has been no overall rise in the Sun’s output since the 1950s. Volcanism cools the Earth, and the climate recovers within a year or two.

Telling natural causes from human causes

A cause is natural if it would happen with no people. Methane from cattle is a human cause because people farm the cattle. Methane is a gas that traps heat. Natural causes: Milankovitch cycles, solar variation and volcanism. Human causes include industry, transport, energy use and farming.

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