BIOLOGY · Stage 8 · Chapter 8: Weather and Climate
Biology 8.3 Climate changes past and present — Ice Ages and Glacial Cycles — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
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Lesson summary
8.3 Climate changes past and present — Ice Ages and Glacial Cycles — Alhussan International Academy — Biology (Stages 7–9) notes: Describe evidence that the climate has changed naturally in the past and explain the natural causes of climate change.Long history — Earth's climate h…
- Warm periods
- Recent cycles
- Atmosphere
- Carbon dioxide levels
- Link to temperature
- Earth's orbit
Section 1 of 6Climate has always changed
- Long history
- Earth's climate has varied greatly over its 4.5 billion year history.
- Warm periods
- in the Age of the Dinosaurs, about 252-66 million years ago, the climate was much warmer than today.
- Fossils show that huge plants and animals lived on Earth then.
- Ice ages = times when the Earth cools and much of the land and sea is covered in ice.
- Plants and animals struggle to survive and many species die out, for example woolly mammoths lived in an ice age.
- Recent cycles
- for about 2.6 million years the climate has swung between cold glacial periods and warmer interglacial periods.
- The last glacial period ended about 11 700 years ago, so we live in an interglacial.
- At the coldest times average temperature was roughly 5 to 6 °C lower and sea level over 100 m lower because water was locked in ice.
Section 2 of 6The atmosphere and carbon dioxide
- Atmosphere
- it is mainly nitrogen and oxygen with a tiny amount of carbon dioxide, and this mixture has changed over millions of years.
- Carbon dioxide levels
- they go up and down over time.
- Volcanoes and living things release carbon dioxide and plants take it in.
- Carbon dioxide traps heat from the ground, keeping the surface warm enough for life.
- Link to temperature
- high carbon dioxide levels make the climate warmer and low levels cause cooling.
- Graphs of past temperature and carbon dioxide show two very similar cycles.
Section 3 of 6Natural causes of climate change
- Earth's orbit
- the shape of the orbit, the tilt of the axis and the wobble of the axis change slowly.
- (Milankovitch cycles)
- They repeat over tens of thousands of years and alter how much sunlight reaches different parts of the planet.
- Cool summers in the far north let snow survive from year to year and build into ice sheets.
- the shape of the orbit, the tilt of the axis and the wobble of the axis change slowly.
- Activity of the Sun
- the Sun is hotter at some times than at others, which warms or cools the Earth.
- Volcanic eruptions and meteorite impacts
- they fill the atmosphere with ash, dust and sulfur gases that stop sunlight reaching the Earth, so the climate cools for a few years.
- Ocean currents
- changes in them also alter the climate.
- Feedback
- ice and snow are white and reflect sunlight, so as ice spreads the Earth reflects more energy and cools further.
- Falling carbon dioxide in cold periods weakens the greenhouse effect too.
Section 4 of 6Length of the natural cycles
- Ice age
- it lasts around 80 000 to 90 000 years.
- Warm period
- it lasts 10 000 to 20 000 years before the climate cools again.
- Last ice age
- it was about 20 000 years ago and took 5000 years for global temperature to rise by 5 °C.
Section 5 of 6Effects on living things
- Ice sheets pushed species towards the equator or into refuges.
- Lower sea levels created land bridges, which let animals and humans migrate, for example between Asia and North America.
- Cold-adapted animals such as woolly mammoths thrived, and many later became extinct as the climate warmed.
- Melting ice
- glaciers carved valleys and lakes formed.
Section 6 of 6Past changes compared with today
| Past changes | Present change |
|---|---|
| Natural causes: orbit, volcanoes | Mainly human: burning fossil fuels, deforestation |
| Changes took thousands of years | Warming is occurring within about 100 to 150 years |
| Species could slowly migrate or adapt | Rapid change gives species little time |
- Rate
- average temperature has risen by about 1 °C in just 100 years, much faster than the natural cycles would give.
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