Page 74 - The World About Us

Ice core
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1.1.1
2.2.32.3.1

What is the evidence for climate change?

Discussion of the changing climate of the Quaternary years are marked by more narrow rings.
involves being able to iden fy global temperatures and how Cores can be drilled into the centre of living trees to
they have changed over the last 2.52 million years. Since remove a sample without having to cut the tree down.
accurate thermometers have only been available for li le Analysis of these rings can give valuable climate data.
over 100 years, how do we know that temperatures have
been fluctua ng over such long periods of me? However, the data from tree rings is limited to the age of
the tree. Even the most ancient of trees rarely live for more
Cultural items than 2,000 years. In 2016, NASA scien sts used
dendrochronology to suggest that areas of the Middle East
Evidence for the ‘Li le Ice Age’ comes from wri en were experiencing the worst drought in 900 years.
records kept by places such as monasteries and manor
houses, as well as personal diaries of the me. Pain ngs of Fig.204 Drilling ice core samples, Antacr ca.
the 'ice fairs' held on the frozen River Thames support
wri en evidence that mes then were colder than today.
Even older cave pain ngs display images of the animals
present as long ago as 40,000 years. While clearly these
cultural items cannot give us an accurate temperature of the
mes, they can give a flavour of the changing climate.

Ice cores

In Antarc ca and Greenland, snow has fallen and been
compacted into ice for hundreds of thousands of years. Each
year's snow is slowly compressed by the layers above into
solid ice. In some places the ice has become almost 5km
thick.
Fig.202 Lascaux cave pain ngs, France. Each layer becomes a dis nct record of the clima c
condi ons present when the water was evaporated from
Dendrochronology the seas before falling as snow. The ice at the base of some
ice sheets may be as old as 1.5 million years.
As a tree grows, each season of growth (and season of
dormancy) leaves a dis nct ring within the wood. This gives Scien sts are able to drill cylindrical cores deep into the
wood its characteris c 'grain' but also creates a record of ice sheet. Careful recording of each core sample allows every
climate change. ice layer to be dated to a specific year or few years. Chemical
analysis of the water molecules, specifically the propor on of
In the trees of Northern Europe's temperate forests,
warmer, we er years (which are more advantageous for Oxygen-16 and Oxygen-18 isotopes in the H₂O molecules,
growth) are marked by wider, thicker rings. Colder and drier allows for a rela vely accurate predic on of mean global
temperatures when the water evaporated from the sea.
Fig.203 Tree rings can show seasonal and annual climate.
Analysis of the air trapped in ny bubbles also provides
clues to atmospheric composi on. Ice cores in Antarc ca,
drilled to a depth of 3.2km, have enabled scien sts to
produce accurate climate data for the last 800,000 years.
Ice cores also record other drama c events, such as large
volcanic erup ons. Layers of volcanic ash trapped in specific
layers can be mapped to individual erup ons (see figure
201). An analysis of the ice before and a er the erup ons can
indicate the impact of these events on the global climate (see
page 76 and 77).

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The climate has changed from the start of the Quaternary period.