Climate change - the evidence

The climate is constantly changing, it has and always will.

1) the quaternary period is the most recent geological time period - 2.6 million years ago till now.

2) in the period before quaternary, the earths climate was warmer and stable.

3) during the quaternary - global temperatures shifted between cold glacial periods that last around 100 000 years, and warmer interglacial periods that last for around 10 000 years.

4) last glacial period - 15 000 years ago - been warming since then.

5) Global warming describes the sharp rise in global temperatures over the last century - its a type of climate change. 

1) ice sheets are made up of layers of ice - one layer is formed each year.

2) scientists drill into ice sheets to get long cores of ice.

• by analysing the gases trapped in the layers of ice, they can tell what the temperature was each year.

3) the remains of organisms found in cores taken from ocean sediments can be analysed. this can extend the temperature record back at least 5 million years

1) as a tree grows, each year it forms a new ring.

• the tree rings are thicker in warm, wet conditions.

2) scientists take cores and count the rings to find the age of a tree.

• the thickness of each ring shows what the climate was like

3) reliable source of evidence of climate change for past 10 000 years.

1) pollen from plants gets preserved in sediment 

• e.g. at the bottom of lakes or in peak bogs

2) scientists can identify and date the preserved pollen to show which species were living at that time.

3) scientists know the conditions that the plants live in now, so preserved pollen from similar plants shows that climate conditions were similar.

1) since the 1850s global temperatures have been measured accurately using thermometers.

• reliable but short-term record of temperature change.

2) historical records can extend the record of climate change from further back.

• e.g. harvest dates, newspaper weather records.