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Evidence for climate change

Evidence for climate change happening comes from many different sources that confirm each other. Together, the data show that we are now living in the hottest average temperatures for 2000 years.

Ice Cores

Ice Cores

When snow falls to the ground it traps tiny amounts of air between the snow flakes. As more snow falls, the weight above compresses the snow below into ice, trapping these tiny pockets of air. These form a record of the air composition at the time the snow fell. The deeper down the air pocket, the older the air.

Scientists have drilled into the arctic snow, down through hundreds of metres of ice, extracting ice cores and thus air pockets from thousands of years ago. By analysing the gases in these and how far down they are in the ice core, they can work out how much carbon dioxide and other gases were present in the air when the snow fell and how old it is.

Mud cores

Mud cores

In some parts of the world’s oceans, the sea floor is made of mud hundreds of metres thick. Tiny sea creatures have lived and died over vast numbers of years, falling to the sea floor to become mud. By extracting cores of mud at increasing depths, scientists can in effect look back through time at the remains of ancient sea creatues.

Sea shells = CO2

Some tiny molluscs grew shells, which still be seen in the mud. Since they build shells by combining calcium in the sea water with carbon dioxide, the thickness of their shells gives a good indication of how much CO2 was present in the water when they lived. Plotting the thickness of their shells through the depth of mud gives a pattern that shows changes in CO2 in the atmosphere over thousands of years.

Pollen = temperature

Also buried in the mud are grains of pollen from plants that were growing nearby at the time the mud was formed. Because different plants grow at specific temperatures, the presence of pollen from specific species is evidence of the local temperature when the pollen was deposited.



Since the 1950s satellites have recorded temperature data and taken photographs from across the earth. Climate change scientists now have access to data covering over five decades.



Many glaciers around the world are melting at an alarming rate. Look at this website documenting recent and old photos of the same glaciers.


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Limits of scientific knowledge

Any attempt to predict the future cannot be certain. There is no way to know for sure what will happen as any prediction can only be based on the evidence we have at the time. However, we can work out what is more likely or less likely to happen. Science can tell us a range of possible outcomes based on that evidence, where the predictions evolve and become more certain as more evidence is gathered.

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Follow the story

This video shows how evidence for climate change has gradually grown since the 1950's. Notice how much science is a process of experts regularly disagreeing. Debate and managing disagreement in order to come up with better explanations is an essential part of how science eventually arrives at the best evidence.

This is a YouTube video. If you can't see it in your school, ask your teacher to show it to you.

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A summary of climate change evidence by Peter Hadfield, New Scientist correspondent for 14 years, and regular contributor to science programmes for the BBC and ABC (Australia).

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 More videos about the science of climate change from this author


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NOT RATED Toby Joyce(IV-TeMpo-IV) 27-02-13 11:38
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