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3.2. How do we know the climate is changing

Earth’s climate has constantly been changing — even long before humans came into the picture. Most
of these climate changes are attributed to very small variations in Earth’s orbit that change the amount
of solar energy Earth receives.
Scientists use weather stations, ocean buoys, and remote sensing instruments to collect many types
of information about Earth's land, atmosphere, ocean and ice which show the changes in the climate.

Scientists study:

- trees (the colour and width of tree rings provide information on how old a tree is and what the
weather conditions were like during each year of that tree’s life; eg. tree rings usually grow
wider in warm, wet years and they are thinner in years when it is cold and dry)
- ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers (layers of ice give
clues about every year of Earth's history back to the time the deepest layer was formed – the
ice contains bubbles of the air from each year; scientists analyze the bubbles in each layer to
see how much CO2 they contain)
- sediment cores from the bottoms of lakes or the ocean floor (they provide evidence of climate
variation over time; eg. the composition of the sediment – for example, the amount of iron it
carries – differs between wet and dry periods)

This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times
faster than the average rate of ice-age-recovery warming. Carbon dioxide from human activity is
increasing more than 250 times faster than it did from natural sources after the last Ice Age.

1
This body of data, collected over many years, reveals the signals of a changing climate .

1 https://climate.nasa.gov/evidence/

This project has been funded with support from the European Commission. This communication reflects the
views only of the author, and the Commission cannot be held responsible for any use which may be made of the

information contained therein.