Climate change · GCSE Geography

Evidence

The Quaternary period is the last 2.6 million years. It has had cold glacial periods and warmer interglacial periods, and we are in an interglacial now.
Evidence of past climate: ice cores (air bubbles trapped in ice show past temperatures and carbon dioxide levels, going back about 800,000 years), tree rings (thicker rings grow in warm, wet years), and historical records such as paintings, diaries and harvest dates.
Evidence of recent warming: temperature records since the 1850s show the world has warmed by more than 1 °C since the late 1800s. Sea levels are rising, and glaciers and Arctic sea ice are shrinking.

Orbital changes (Milankovitch cycles): the shape of the Earth's orbit, its tilt and its wobble change slowly, changing how much energy reaches the Earth. They match the glacial and interglacial cycles.
Solar output: the Sun's energy varies slightly. The Maunder Minimum (1645–1715), when there were very few sunspots, matches the coldest part of the Little Ice Age.
Volcanic eruptions: ash and sulphur dioxide block sunlight, cooling the Earth for a year or two, as after Mount Pinatubo erupted in 1991.

Greenhouse gases, such as carbon dioxide and methane, trap heat in the atmosphere. Humans have added more, strengthening the natural greenhouse effect.
Burning fossil fuels (coal, oil and gas) for electricity, transport and industry releases carbon dioxide. Farming releases methane from cattle and rice paddies. Deforestation removes trees that absorb carbon dioxide, and burning them releases more.

On the environment: rising sea levels (warming water expands and land ice melts), shrinking glaciers and ice sheets, coral bleaching, changing habitats and more extreme weather.
On people: coastal flooding in low-lying places such as Bangladesh and the Maldives, water shortages and droughts, lower crop yields in some places, deaths from heatwaves, and people forced to move. There are some benefits, such as longer growing seasons in cooler places.

Mitigation reduces the causes: renewable energy, carbon capture and storage, planting trees, and international agreements. The Paris Agreement (2015) aims to keep warming well below 2 °C, and to try to limit it to 1.5 °C.
Adaptation copes with the effects: drought-resistant crops, storing and saving water, flood defences, raising buildings and managing coastal retreat.

Quaternary period: The last 2.6 million years of the Earth's history.
Ice core: A cylinder of ice drilled from an ice sheet, containing evidence of past climates.
Greenhouse effect: The natural trapping of heat by gases in the atmosphere, which keeps the Earth warm.
Enhanced greenhouse effect: Extra warming caused by the greenhouse gases added by humans.
Fossil fuel: A fuel formed from ancient plants and animals, such as coal, oil or gas.
Milankovitch cycles: Slow changes in the Earth's orbit, tilt and wobble that affect the climate.
Mitigation: Reducing the causes of climate change.
Adaptation: Changing the way people live to cope with the effects of climate change.
Carbon capture: Collecting carbon dioxide from power stations and storing it underground.