CSIRO logoCSIRO video

Understanding why the Earth system is warming

YouTube Ref: http://youtu.be/tzSt4byjvIY

Date: 27 September, 2013


[Music plays and text appears: Understanding why our Earth system is warming]

[Image changes to an animated image of Earth, text appears: Global change]

Dr Pep Canadell: Climate change it is like a global problem in the sense that the atmosphere is a commons for society. What we Australians do or somebody else does at the other end of the world, it actually all gets mixed within a year. [Image has changed to Dr Pep Canadell, Global Carbon Project – CSIRO]

So we really need to develop strategies, which are strategies working globally in partnership. Both in the science to understand it, but also in the way we address the mitigation ultimately.

[Image has changed to Dr John Church, Research Scientist – CSIRO]

Dr John Church: Well the Earth is warming, principally, because we're releasing greenhouse gases into the atmosphere. These trap the outgoing long wave radiation and lead to a warming Earth. The energy, total energy in the Earth's system increases and much of that energy is locked up in the oceans.

[Image changes to an aerial shot of an ocean, text appears: Changes to our oceans]

Dr Steve Rintoul: I'm an oceanographer and the oceans are important to climate because they store huge amounts of heat and carbon dioxide. And in fact about 93 per cent of the extra heat that's been stored by the Earth over the last 50-years, is found in the ocean. So I we want to understand climate change and track how it's evolving we really need to be measuring the ocean. And that's relevant to current discussions about the rate at which the Earth has warmed recently.

[Image has changed to Dr Steve Rintoul, Research Scientist – CSIRO]

So, over the last decade or so the speed at which the surface has been warming has slowed a bit, it's still warming, and the last decade is still the warmest decade in the instrumental record. But the rate of warming has slowed, even though the amount of Co2 in the atmosphere has increased, so that sounds like a surprise at first, but we're beginning to understand exactly how that's happening.

[Image changes to show glaciers, text appears: Changes to ice and sea level]

Dr John Church: We also see other changes; glaciers are continuing to lose mass. The sea ice, particularly in the Artic, is continuing to retreat and the ice sheets of Greenland and Antarctica are contributing by losing mass contributing to sea level rise which is continuing to rise at a faster rate over the last 20 years than over the 20th century as a whole.

[Image changes to a shot of sky and clouds, text appears: Changing rates of warming]

Dr Steve Rintoul: These pauses or periods when the earth warms more slowly than average are not unusual. They happen in the climate system frequently.

[Image has changed back to Dr Rintoul] The second point is that we now understand what's happening and part of what's happening is that the heat in the earth's system is moving around and, in particular, more of the heat that used to be near the surface of the ocean has moved deeper in the ocean so if we look at the... how the heat that's stored by the earth has changed over the last decade and include the upper 2000 metres of the ocean we see that the earth has continued to warm during this last decade just like it has in the decades before.

[Image changes to an animated image of Earth with the sun seen behind it]

The other factor that contributes is that the sun that goes through a cycle of about a decade of energy output from the sun increasing and then decreasing has been in a decreasing phase over the last ten years and that's now turning around.

[Image changes to show a volcano with smoke bellowing out of it]

And finally there have been a few small volcanoes and volcanoes put small particles up into the atmosphere and that tends to shield the earth from some of the sun's energy and that also causes the earth to cool. So the combination of those factors can explain why the surface of the earth both on land and in the ocean has warmed less rapidly over the last decade than it did in the decade before.

[Image has changed back to Dr Rintoul]

[Image changes to show mountains and clouds, text appears: Greenhouse gases]

Dr Pep Canadell: So greenhouse gases are gases which are naturally occurring in the atmosphere.

[Image has changed to Dr Canadell]

They trap some of the energy from the sun and allows the Earth to be a very comfortable place as a whole to live in, so a lot of the human activities specifically the combustion of fossil fuels, coal, gas and oils and also what we call land use change deforestation, largely the burning of the forest, are the main causes of greenhouse gases.

[Image changes to different pictures of factories with smoke stacks and the deforestation process]

[An aerial shot of Cape Grim appears on screen with the text: Cape Grim Baseline Air Pollution Station, Tasmania monitors and studies global atmospheric composition]

So we have now acceleration in the accumulation of these greenhouse gases and that's why there is a warming and warming actually leads to other changes in climate patterns including precipitation and others.

[Image changes to show hills and a dark stormy sky with bolts of lightning, text appears: Climate models – predicting future change]

Dr John Church: To project future changes just extrapolating the past is not sufficient.

[Image has changed to Dr Church]

[Image changes to show a Climate Model simulator and small changes are seen the world map as the year is adjusted to 2036 and beyond]

What we have to do is build an understanding of what's happened in the past, put this understanding in climate models which could then simulate the past, test them against the past and then use those climate models with scenarios of how our society might behave in the future in terms of emitting greenhouse gases and run those models into the future to predict future conditions.

[Image changes to a show a shot of the ocean, text appears: Studying the oceans to understand climate]

Dr Steve Rintoul: So to study the ocean to actually measure how the ocean's changing we use a variety of tools.

[Image changes to show an instrument being lowered into the water from a ship]

We use ships that we lower instruments from, ships that scan the ocean, use satellites, use instruments that we anchor to the sea floor for a year or two and we use these days simple robots, floats that drift through the ocean currents at a depth of 1 kilometre. Every ten days they drop drown to 2 kilometres and then rise up to the surface measuring temperature and salinity.

[Image changes to show an animated satellite beaming images back to Earth]

We transfer that data by satellite, sink back down and do it all again and do that for five years or so for each float. There are about 3600 of these floats now drifting around the world oceans and so in a real sense we're measuring the oceans for the first time.

[Image changes to show a shot of the ocean, text appears: Science informing our climate future]

[Image has changed to Dr Canadell] Dr Pep Canadell: We put a huge amount of effort in taking all these measurements and expensive measurements and expensive development of modelling capability but also we're putting an increasing amount of time in packaging this information in ways that can be readily used and understood and make a difference for the things that policy needs information on.

[Image has changed to Dr Rintoul]

Dr Steve Rintoul: The last decade has been the warmest in the instrumental record and each of the last few decades has been warmer than the last and that's part of the signal of greenhouse warming. The last 12 months for Australia has been the warmest on record and that is the combination of the slow continued warming due to greenhouse warming and the variability of the climate system and so we will get years that will be cooler than this last one but that's what we expect to see. The climate... the warming of the earth and the warming over Australia will not just be a steady trend, it'll go up and down a little bit. But the trend over longer time periods which is what you need to look at in order to detect a signal of climate change has been up and will continue to be warming in the future.

[Image has changed to Dr Church]

Dr John Church: Sea levels are continuing to rise. The amount of rise depends on future emissions of greenhouse gases.

[Image has changed to show city buildings with the beach next to it]

Larger emissions lead to larger rises both during the 21st century and beyond so the amount of sea level rise that Australia will have to deal with is impacted by the degree to which we mitigate ours and the world's emissions of greenhouse gases. We cannot stop all sea level rise. We will have to adapt but the amount of adaptation that we have to do will depend on our future emissions.

[Image changes to show city buildings and cars on roads and then changes to show a wind farm]

[Image has changed to Dr Rintoul]

Dr Steve Rintoul: So the challenge for climate science in the future, it's clear that the Earth is warming and it's clear that human activities have contributed. What is still more difficult to do is to project regional changes of temperature and, in particular, precipitation and that's crucial because the decisions that society will make to adapt to the climate change that we don't avoid requires information at those scales, at local and regional scales because that's where people make decisions.

[Image has changed back to show the ocean and shots of sea ice]

And so a challenge for the climate science is to deliver that sort of information, regional projections of changes in climate that can inform decision-makers about both how hard we're going to work to slow down the rate of climate change by mitigating, by reducing greenhouse gas emissions and how we can most effectively adapt to the climate change that we're not going to avoid.

[Credits roll: Film by Chris Johnson – CSIRO. Special thanks to Dr Pep Canadell, Dr Steven Rintoul, Dr John Church, Craig Macaulay, Simon Torok, Kim Marshall-Brown. Additional footage Andy Marsh, Nick Roden. Stock footage: shutterstock.com. Music: themusicbed.com, freemusicarchive.org]

[Music plays, CSIRO logo appears with the following text: Big ideas start here www.csiro.au]

CSIRO’s Official YouTube Channel: http://www.youtube.com/user/csiro/