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Climate change from the Ice Age to today

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Earth's climate has always changed. What is different now is how fast it is warming, and the main cause: us.

Ice ages and natural change

Over the last 2.6 million years Earth has swung between cold glacial periods and warmer interglacial periods.
At the height of the last glacial, about 20,000 years ago, ice sheets covered much of Britain and sea levels were far lower; Britain was joined to mainland Europe by land.
We live in a warm interglacial that began about 11,700 years ago.
Natural causes of change: changes in Earth's orbit and tilt, changes in the sun's output, and large volcanic eruptions.

Evidence

Ice cores from Antarctica contain bubbles of ancient air, showing past temperatures and carbon dioxide levels for hundreds of thousands of years.
Tree rings, pollen in old sediments and historical records also help.
From about the 1300s to the 1800s Europe had a cooler spell called the Little Ice Age, when the River Thames sometimes froze and frost fairs were held on it.

Climate change today

The greenhouse effect keeps Earth warm: gases like carbon dioxide and methane trap heat.
Since the Industrial Revolution, burning fossil fuels and cutting down forests have added more greenhouse gases: the enhanced greenhouse effect. Carbon dioxide has risen from about 280 parts per million before industrialisation to over 400 today.
The IPCC reports that global surface temperature in 2011 to 2020 was about 1.1 degrees C warmer than in 1850 to 1900.
Effects: melting ice, rising sea levels and more extreme weather. Responses: mitigation (cutting emissions, such as using renewable energy) and adaptation (coping, such as flood defences). In the Paris Agreement (2015) countries agreed to try to keep warming well below 2 degrees C.
Worked example

How is climate change today different from changes since the Ice Age?

  1. Past changes were caused naturally, by orbit changes, the sun and volcanoes.
  2. Today's warming is mainly caused by people adding greenhouse gases.
  3. It is also happening much faster than most natural changes.

Answer: Today's change is mainly human-caused and much faster than most past natural change.

Key idea

Glacial and interglacial periods over 2.6 million years; last glacial peak about 20,000 years ago; our interglacial began about 11,700 years ago. Natural causes: orbit, sun, volcanoes. Evidence: ice cores, tree rings, pollen. Burning fossil fuels has raised CO2 from about 280 ppm to over 400 ppm; warming about 1.1 degrees C (2011 to 2020). Mitigation and adaptation; Paris Agreement 2015.

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