Climate change

• Earth was formed about 4.5 billion years ago
• Earth's climate has changed continually since it was formed
• Earth has mostly been warmer than now, with no ice anywhere
• There have been many ice ages, when Earth cooled and ice sheets and glaciers spread
• Graph A


  Shows changes in Earth's average temperature compared to today over the last 5 million years
• The dashed line represents Earth's average temperature today, labelled 0
• The zig-zag line shows how the average temperature rose and fell compared with today's
• In the period shown, Earth was almost always warmer than today - sometimes over 2 °C warmer
• The period from 2.6 million years ago until today is called the Quaternary period, and has been almost always colder than today
• Ice sheets spread from the poles each time Earth grew colder, giving ice ages. They retreated again as Earth warmed
• The last ice age began around 110,000 years ago, and about a third of Earth's land surface got covered in ice sheets, including much of Britain
• About 12,000 years ago, Earth began to warm up, and the only ice that remains today is around the poles, and up high mountains
• Woolly mammoths first appeared about 400,000 years ago, and disappeared 4,000 years ago either because we hunted them, or Earth grew too warm for them, or both
• In the last ice age, sea levels fell by 120 m, exposing sea floor as 'land bridges' and allowing humans to migrate
• Land bridges joined Britain to Ireland and France
• The first human species (Homo habilis) appeared about 2.5 million years ago
• We modern humans (Homo sapiens) appeared around 0.2 million years ago
• Climate detectives


  Scientists who study past climate changes
• We have been measuring climate properly for less than 200 years
• Scientists look for clues about past climates in many places
• Every year, billions of tonnes of dead organisms, and particles carried by the wind and rivers, settle on the ocean floor
• Ocean sediment


  1. Builds up layer by layer over millions of years

  2. Drilled from the ocean floor

  3. Studied layer by layer using radiometric dating
• Radiometric dating


  • Tells scientists the age of a layer and what the climate was like then
• Ice sheets


  1. Build up in layers from snow

  2. Analysis of ice cores tells scientists when the snow fell, the temperature then, and what gases were in the air
• Tree rings


  1. Counting the rings tells us a tree's age

  2. Their widths tell us about changing climates

  3. Can drill a plug from a living tree
• Scientists must also find out why climate changed
• The data from above, matched to data from astronomers and others, has helped scientists to find the answers
• Global warming


  The warming of Earth
• Earth is getting warmer, so climates are changing in countries across Earth
• Average global temperatures from 1850 to 2018


  • Shift from blue to red shows how Earth has warmed
  • Temperature rose by about 1°C between 1850 and 2018
  • An extra 1°C can melt ice
• Warming of Earth


  • Uneven
  • Some places had warmed by less than 0.5°C
  • The Arctic had warmed by more than 2.5°C
• As temperature rises, the patterns of rainfall and wind and ocean currents change too
• Ice reflects sunlight away because it's white


  When ice melts, the darker surfaces absorb more sunlight, and then warm the air so more ice melts
• If Greenland's ice sheet melts, sea levels will rise by over 7 metres
• When ice melts, the ground warms up, because darker surfaces absorb more sunlight. It's the albedo effect.