Natural & Human Climate Change
A Climate That Has Always Changed
Earth’s climate has never stood still. The most recent geological period, the Quaternary, has cycled between cold glacial periods (when ice sheets advanced over much of northern Europe and North America) and warmer interglacial periods. The last glacial maximum was around 18,000 years ago, when ice covered most of Britain north of the Thames. We are currently in an interglacial — the Holocene — that began about 11,700 years ago. Within that long-term picture, climate has wobbled noticeably even in the last thousand years, before any human industrial activity at all.
Natural climate change has three main drivers: orbital changes (Milankovitch cycles), variations in solar output, and major volcanic eruptions. Each operates on a different timescale.
Natural Causes of Climate Change
Milankovitch cycles describe slow wobbles in Earth’s orbit. Three cycles overlap: eccentricity (the orbit’s shape over 100,000 years), obliquity (axial tilt, 41,000 years) and precession (axial wobble, 26,000 years). Together they change how much summer sunshine high latitudes receive, triggering the start and end of glacial periods. Solar variation includes 11-year sunspot cycles and longer trends; the ‘Maunder Minimum’ (1645–1715), when sunspots almost disappeared, coincided with the coldest part of the Little Ice Age. Volcanism can cool the planet for years — the 1815 Tambora eruption produced the ‘year without a summer’ in 1816 because ash and sulphur particles reflected sunlight back into space.
Evidence for Past Climate Change
Geographers reconstruct past climate from natural archives. Ice cores drilled in Antarctica and Greenland trap tiny air bubbles — chemists measure their CO2 content directly, going back over 800,000 years. Tree rings show wide growth in warm wet years and narrow growth in cold or dry ones. Pollen records in lake sediments preserve the dominant vegetation of each century, and vegetation tracks climate. Historical sources — harvest records, paintings of frost fairs on the Thames, monastery diaries — complete the picture for the last thousand years.
The Enhanced Greenhouse Effect
The natural greenhouse effect makes Earth liveable. Greenhouse gases (water vapour, carbon dioxide, methane, nitrous oxide) trap some of the heat radiated from Earth’s surface, holding the planet at around 15°C rather than -18°C. The problem is that human activity has loaded the atmosphere with extra greenhouse gases, intensifying that natural effect. The enhanced greenhouse effect is the result. Atmospheric CO2 has risen from about 280 parts per million (ppm) before the Industrial Revolution to over 420 ppm today — the highest level for at least three million years. Average global temperature has risen by about 1.2°C since 1850.
Burning fossil fuels (coal, oil, gas) for industry, energy and transport releases carbon that was locked away for hundreds of millions of years. Agriculture contributes methane (cattle, rice paddies) and nitrous oxide (fertilisers). Tropical deforestation not only releases stored carbon when trees are burned, it also reduces the planet’s ability to absorb future emissions. The biggest single source globally is electricity and heat generation; the fastest growing is transport.
Negative Effects of Today’s Climate Change
The impacts cluster around three changes. Crop yields are shifting: heat stress and unreliable rainfall cut maize and wheat yields in Africa and southern Europe, while northern latitudes (parts of Canada and Russia) gain growing degree-days. Sea levels have risen 21 cm since 1880 and are rising faster every decade as polar ice melts and ocean water expands. Low-lying countries like Bangladesh and Tuvalu face existential risk; UK coastal cities including Hull, Portsmouth and Newport will spend billions on raised defences this century. Glaciers are retreating worldwide — the Alps have lost over 50% of their ice volume since 1850, threatening summer water supplies for millions in southern Europe.
Developing countries near the equator suffer earliest and worst from climate change despite emitting the least: hotter starting temperatures, agriculture-dependent economies, and fewer financial resources for adaptation. Developed countries with temperate climates and capital can defend coastlines, breed heat-tolerant crops and air-condition cities. The injustice of this pattern shapes international climate negotiations — richer countries are typically asked to fund adaptation in poorer ones (e.g. the COP27 ‘loss and damage’ fund agreed in 2022).
Atmospheric CO2 has risen from 280 ppm (pre-industrial) to over 420 ppm today, and average global temperature has risen by about 1.2°C since 1850. The rate is faster than any natural cycle on record.