How do scientists measure climate change?

Back to ‘EcoLogic – Climate Change’

In this section:

How does the climate change naturally?
What’s carbon got to do with climate?
How do scientists measure climate change?
What can we do about climate change?

Climatic change happens over many years so it might be hard to notice dramatic changes over just one human lifetime. Scientists are using modern tools to read clues that were left long ago, and building a picture of what’s happening to the Earth’s climate. There are thousands of scientists studying different aspects of climate science including chemists, biologists, physicists, oceanographers and geologists. They’re looking everywhere. Scientists are trained to be skeptical and to debate ideas until they all agree. Even then, there’s always room for new evidence that can help refine a theory and deepen our understanding.

Reading rings to probe the past

Trees, corals and limestone deposits (speleotherms), such as stalactites and stalagmites in caves, hold clues about ancient climates. Corals and trees can live for thousands of years. Each year’s growth is recorded as a new layer or ‘growth ring’. The layers provide information about temperature, rainfall and other environmental conditions at the time they were created. The growth rings incorporate materials from the surroundings and thus create a record of the environment’s history.

Cross section of a tree showing growth rings
Every year a tree lays down new growth rings that provide information about local environmental conditions
Cross section of a piece of coral showing growth rings
The rings reflect the way conditions change from year to year on a coral reef. Gift of Australian Institute of Marine Science 2010.
Cross section of a stalagmite showing rings
Rings in stalagmites reflect changes in rainfall and temperature over time. Powerhouse Museum Collection NN1512


Air bubbles in Antarctic ice are time capsules

Ice at the South Pole contains air bubbles that are up to 800 000 years old.

Gloved hands holding a block of ice containing air bubbles
The air bubbles in Antarctic ice can be hundreds of thousands of years old. Photo: CSIRO


Snow traps air bubbles when it falls and is compressed to form ice. Scientists have drilled 3200 metres into the ice to sample air from ancient times. They’ve tested the air in the bubbles to see how much of each gas (eg oxygen, carbon dioxide, nitrogen) it contains. Carbon dioxide levels have gone up and down in cycles of about 100 000 years. The temperatures and carbon dioxide concentrations shown in the graph occurred at Vostok in Antarctica during the last 400 000 years. It seems that when carbon dioxide levels are high, the temperature goes up too.

Graph showing 10,000 year cycles in changes in carbon dioxide and temperature
This graph shows how carbon dioxide in the air and temperatures at Vostok have changed over time. Adapted from Nature 453, 15 May 2008.


Water in the ice holds secrets too

The water in the ice around the bubbles reveals what temperatures were like at the time. The ice is made up of a mix of ordinary water and heavy water (deuterium). At least one of the hydrogen atoms in heavy water is a bit bulkier than normal so it’s harder to evaporate and deposit as snow. Only high temperatures can do the job. So if there’s a lot of heavy water in the ice it indicates that temperatures were high. Scientists use the ratio of heavy to normal water in ice layers to estimate average temperatures at the time the ice was made.

Measuring carbon in the air

Scientists have regularly sampled the Earth’s atmosphere since the 1950s. They’re measuring the carbon dioxide and other gases that contain carbon in the air. Click here to see the latest atmospheric greenhouse gas measurements from CSIRO in Tasmania.

Aerial shot of the beautiful rugged landscape and wind turbines of Cape Grim
Northern Tasmania’s pristine air is sampled regularly at Cape Grim. Photo: Bureau of Meteorology


A man reading a gauge on a metal cylindrical tank in a room stacked high with similar tanks
CSIRO has kept an archive library of air samples since the 1970s. Photo: CSIRO Marine and Atmospheric Research

The Carbon in carbon-dioxide gas exists naturally in two forms (isotopes), carbon-12 and a heavier carbon-13.

Carbon-12 is lighter than Carbon-13 because it has one less neutron.
Diagram showing Carbon-13's make-up
A diagram of carbon 13 showing six electrons, six protons and seven neutrons.


Plants preferentially take in carbon-dioxide that contains carbon-12 so they, and the fossil fuels they turn into, contain almost no carbon-13. Scientists have sampled the air continuously since the 1950s. They’ve found that the type of carbon increasing in the air is carbon-12 and is thus likely to be coming from the burning of fossil fuels.When carbon is burned, carbon dioxide gas is released into the air. It’s measured in parts per million (ppm) by volume, which means the number of units of carbon dioxide per million units of air.

Argo floats measure the oceans

More than 3500 Argo floats are drifting along in the world’s ocean currents. These small robots constantly gather information about temperature and salinity. Each float spends most of the time 2000 metres below the surface but it emerges every ten days to transmit data to satellites.

Diagram showing the progress of the Argo float when measuring ocean salinity
There are thousands of Argofloats taking measurements in the world’s oceans.

Australia’s CSIRO scientists released the first Argo floats in 1999. Today 26 countries are involved, gathering data and building a clear picture of warming oceans.

Men throwing a cylindrical yellow Argo float from a ship into the ocean
Scientists deploy a robotic Argo ocean-profiling float. Photo: Alicia Navidad, CSIRO

Yearly weather records are averaged to describe the climate

Weather is what’s happening outside the window right now. Daily temperature and rainfall has been measured in Australia for the past 200 years. These weather records have documented daily conditions throughout the year. When averaged over a number of years, the records create a picture of prevailing conditions, or climate, in each region. So, climate describes the long term pattern of weather conditions that occurs in a locality. Thermometers and rain gauges are used to collect weather data. These days temperatures are also taken by satellites to reduce the possibility of false high readings due to heat in cities.

Overall, rainfall has dropped in south eastern areas and temperatures have risen in inland regions. Since 2005, temperatures have reached record highs. CSIRO’s climate models suggest that, although we’ll experience more dry days in future, the rainfall will be heavier when it comes.

Arctic sea ice melting away

Polar ice cap as seen from space
This photograph shows the extent of sea ice in the summer of 1983. Photo: NASA/Goddard Space Flight Center Scientific Visualisation Studio
Polar ice cap as seen from space
Satellite photos show that by 2007 the extent of summer sea ice was greatly reduced. Graphic: NASA/Goddard Space Flight Center Scientific Visualisation Studio

These satellite images show how much less summer sea ice there was in 2007 compared with the amount in 1983. Average temperatures are rising faster in Arctic regions than other parts of the Earth. Sea ice is melting rapidly and shipping routes will soon be ice-free all year. When the Arctic was covered with ice the white surface reflected solar radiation back into space. The dark sea surface now absorbs the radiation. This creates a feedback loop that will keep heating the planet. You can see how the extent of summer sea ice has dropped since 1979.

Click here for current information about Arctic sea ice.

If the Arctic heats too much an ocean current known as the Great Ocean Conveyor might slow or stop, making Europe colder. The Great Ocean Conveyor is a current that carries warm water from equatorial regions up the coast of Europe to the Arctic. When it reaches the Arctic, the water cools and sinks, taking oxygen to the ocean depths. Because the current affects the climates of so many countries scientists are keeping an eye on its temperature and flow rate.

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