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Death throes of the climate |
It was realised by the mid-18th century that some gases in the Earth's atmosphere, such as carbon dioxide, trap heat and keep the Earth warm. At the start of the 20th century, a Swedish scientist named Svante Arrhenius put forward the idea that human emissions of carbon dioxide would eventually raise temperatures. He didn't see this as a particularly bad thing, and most scientists at the time were sceptical that humans could burn fossil fuels fast enough to have a noticeable impact at all.
So, although the idea that mankind could influence Earth's global temperature was proposed over a century ago, it wasn't until relatively recently that scientists were able to confirm this with confidence. Data had to be gathered from around the world, technology had to develop to allow us to analyse that data, and basic advances in physics and other disciplines had to come about before we could understand it. What we now know about the climate is thanks to literally generations of dedicated researchers.
However, it is also easier to observe human caused climate change today because we've put so much more carbon dioxide into the climate system over the past century that the impacts of climate change are now clearly visible, affecting people and ecosystems all over the world.. More cars, more factories, and more power plants - all are changing the climate faster than was previously possible - and causing more obvious changes.
Taking the planet's temperature
To get an accurate picture of how warm the Earth is, you need measurements from all over because the whole planet does not heat up at the same rate. In fact, some parts might even cool down while the world as a whole heats up. Also, many temperature readings are needed over time to develop an accurate long-term picture. In order to develop a global temperature history, researchers have had to travel to the farthest corners of the Earth, and come up with ways to "go back in time".
Some sources of past temperature data:
- Historical records - Includes sources like ship's logs, farmer's diaries and newspaper articles. When carefully evaluated these can provide can provide both quantitative and qualitative data.
- Personal accounts and oral histories - Useful information can be gathered especially from the older generations of indigenous people who have always relied on nature for their survival, and so are particularly observant of changes over the past decades.
- Direct (e.g. thermometer) measurements - Only go back around 300 years, and are very sparse until about 150 years ago. Also, differences in thermometer types and other variables have to be taken into account.
- Data collected by balloon and satellite - Very useful, but only available since 1979.
- Tree ring thickness - Width and density varies depending on growing conditions.
- Ocean and lake sediments - Billions of tons of sediments accumulate each year. The tiny preserved fossils and chemicals in layers of sediment can be used interpret past climate.
- Coral skeletons - The water temperature that the coral grew in can be determined from trace metals, oxygen and the isotopes of oxygen contained in its skeleton.
- Fossil pollen - Each plant has uniquely shaped pollen. Knowing what plants were growing at a particular time in the fossil record lets scientists make inferences about what the climate was like at the time.
- Ice cores - Over the centuries snow falling on high mountains and the polar ice caps packs down and becomes solid ice. Dust and air bubbles trapped in this ice provide valuable climate data. For example, the air trapped in the ice serves as a record of carbon dioxide concentrations across the millennia.
- Observed melting - Rates of glacial retreat, permafrost thaw, shrinking polar ice caps and reduction in Arctic sea ice are indicators of both short and long term climate change.
The important thing is not to look at any one source of data independently, but instead to take them together. This produces a scientifically compelling picture of a warming world that matches with the corresponding increase in greenhouse gasses.
Predicting the climate future
Global climate models are mathematical representations of the real world's climate. Some models are attempts by scientists to boil the complex behaviour of the climate down to (comparatively!) simple formulas in an attempt to understand the forces at work. However, when people talk about specific predictions of long term climate behaviour they are usually talking about general circulation models. In these models, the equations are tweaked (within reason) until the model is able to predict past and present conditions, as accurately as possible, when tested against actual observations of past and present conditions.
Since it's impossible to know every last variable, and because the model will never match the real world perfectly, scientists compensate by running each model over and over, while making tiny changes to the starting conditions (increasing the wind speed over Detroit by one percent, for example) and other factors. This way they can get an idea of the different possible outcomes. If one result occurs more frequently then another then it's the more likely outcome.
In the end, each model predicts a range of possible outcomes. For example, the IPCC, taking into account all of the different available models, settled on a projected global temperature rise of 1.4 - 5.8° Celsius (about 3 to 8° Fahrenheit). No one can say exactly how much the temperature will increase over the next hundred years, but with a couple of caveats it is a safe bet that it will be within this range.
The caveats
One thing climate models can not predict are all the possible effects of feedback mechanisms, which might help stabilise the climate or cause the climate to change much faster and in unpredictable ways. Of course, it would be irresponsible to ignore the climate models and hope for the best because of these uncertainties. See our feedback effects page for more information.
Another thing these models can not really predict is human behaviour, and ingenuity. We could burn more fossil fuels than expected, and end up with a hotter planet then even the worst case scenario. Or we could deploy renewable energy and energy efficiency solutions faster then thought possible - eliminating the likelihood of the higher temperature ranges.
US National Oceanic and Atmospheric Administration - Climate proxy data
American Institute of Physics - History of climate change research
T he Climate Change Connection - Climate research
ClimatePrediction.Net - Distributed computing climate modelling project (join the Greenpeace team on the project!)
Reports
Energy Revolution: a sustainable pathway to a clean energy future for Europe
27 September 2005
The Greenpeace energy revolution scenario: A sustainable pathway to a clean energy future for Europe Greenpeace and the Institute of Technical Thermodynamics of the German Aerospace Center (DLR), have developed a blueprint for the EU energy supply that shows how Europe can lead the way to a sustainable pathway to a clean energy future.
Impacts of climate change on glaciers around the world
09 February 2004
The Patagonian ice-fields of Chile and Argentina, the largest non-Antarctic ice masses in the Southern Hemisphere, are melting faster than any other glaciers on Earth. They have lost 42 cubic kilometres of ice every year over the past seven years, which is equivalent to the volume of ten thousand large football stadiums. Today, they account for nearly 10 per cent of global sea-level change caused by mountain glaciers, according to a new study by NASA and Chile's Centro de Estudios Cientificos, and the rate at which they are melting is accelerating.
The State of the Cryosphere: What the Ice is Telling us
28 November 2003
The cryosphere comprises all the frozen water and soil on the surface of the Earth. The book from Cambridge University Press, "Mass Balance of the Cryosphere", to be published in January 2004, focuses on two key components of this sensitive environment: land ice, in the form of ice sheets, caps and glaciers, and sea ice. These are important indicators of both short and long- term climate change. Written by a team of 23 expert scientists and edited by Dr Jonathan Bamber and Dr Anthony Payne of Bristol University, the book warns that the cryosphere is extremely sensitive to climate change and we ignore at our peril the dramatic and disturbing trends that have already been observed globally.
Climate change and coral bleaching
17 June 2001
This scientific study concludes that if climate change is not stopped, coral bleaching is set to steadily increase in frequency and intensity all over the world until it occurs annually by 2030 - 2070.
Answers from the Ice Edge
01 June 1998
This report is about changes Alaska Native peoples of the northern Bering and Chukchi seas observe in their surroundings. Climate change is a grave threat to northern ecosystems and thus to the subsistence way of life that is the heart of Yup'ik and Inupiat cultures.
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