Sunday, March 28, 2010
Saturday, March 27, 2010
Thursday, March 25, 2010
The Economist on climate change science
Summary/excerpts of a recent Economist article on Climate change science, mostly for my own reference:
Full article here:
http://www.economist.com/displaystory.cfm?story_id=15719298
======
In any complex scientific picture of the world there will be gaps, misperceptions and mistakes. Whether your impression is dominated by the whole or the holes will depend on your attitude to the project at hand. You might say that some see a jigsaw where others see a house of cards. Jigsaw types have in mind an overall picture and are open to bits being taken out, moved around or abandoned should they not fit. Those who see houses of cards think that if any piece is removed, the whole lot falls down. When it comes to climate, academic scientists are jigsaw types, dissenters from their view house-of-cards-ists.
The defenders of the consensus tend to stress the general consilience of their efforts—the way that data, theory and modelling back each other up. Doubters see this as a thoroughgoing version of “confirmation bias”, the tendency people have to select the evidence that agrees with their original outlook.
No one doubts that carbon dioxide is a greenhouse gas, good at absorbing infra-red radiation. It is also well established that human activity is putting more of it into the atmosphere than natural processes can currently remove. Measurements made since the 1950s show the level of carbon dioxide rising year on year, from 316 parts per million (ppm) in 1959 to 387ppm in 2009. Less direct records show that the rise began about 1750, and that the level was stable at around 280ppm for about 10,000 years before that. This fits with human history: in the middle of the 18th century people started to burn fossil fuels in order to power industrial machinery. Analysis of carbon isotopes, among other things, shows that the carbon dioxide from industry accounts for most of the build-up in the atmosphere.
Disagreement is not with the level of C02 or that it comes from human activity. It is with the warming associated with a particular level of CO2. Problems:
Background natural climate cycles.
Climate is a complex non-linear system
Oceans can absorb heat and add inertia to the climate system, so atmosphere warms more slowly than expected.
On the data front: There are three records of land-surface temperature put together from thermometer readings in common use by climatologists, one of which is compiled at the Climatic Research Unit of e-mail infamy. They all show warming, and, within academia, their reliability is widely accepted. Various industrious bloggers are not so convinced.
Pure theory says that doubling Co2 will result in 1 degree C of warming, which is not so problematic. "climate sensitivity". However there are feedback effects that can increase this. The most important involve water vapour and clouds. Warming air will absorb water vapour (powerful greenhouse gas) which is a positive feedback loop for warming. There is scientific uncertainity about how much the water vapour adds, one estimate is 1.7 degrees C, up from the 1 degree C above.
Another point of contention: greenhouse warming should cause warming down below and cooling in the stratosphere. Earlier observations did not corraborate this, but now evidence is building up in favour.
Clouds have both a cooling effect (reflecting sunlight from the upper atmosphere), as well as a greenhouse effect. Sorting these two out to get the net is complicated.
Another source of evidence is the climate of the past, like ice ages and the associated CO2 and other factors that contributed to it. The temperature records of the past millenium is one particular hotspot of debate. Tree rings is one source of data. A 1998 Nature article found a 'hockey stick' shape for temperatures of the last century, mostly flat but with the blip towards the end of the 20th century. This paper is widely contested by sceptics. One contestation is that this curve does not account for the 'medieval warm period' ; when, it is believed, temperatures were as warm or warmer than now.
The most accurate recent climate data cannot be used easily for checking the quality of models because of complexities like aerosols in the atmosphere whose effects are not known well enough so their effect is parameterized in the model instead of being strictly modelled. This also leads to accusations that they are parameterised in such a way as to make the models show higher levels of warming.
Full article here:
http://www.economist.com/displaystory.cfm?story_id=15719298
======
In any complex scientific picture of the world there will be gaps, misperceptions and mistakes. Whether your impression is dominated by the whole or the holes will depend on your attitude to the project at hand. You might say that some see a jigsaw where others see a house of cards. Jigsaw types have in mind an overall picture and are open to bits being taken out, moved around or abandoned should they not fit. Those who see houses of cards think that if any piece is removed, the whole lot falls down. When it comes to climate, academic scientists are jigsaw types, dissenters from their view house-of-cards-ists.
The defenders of the consensus tend to stress the general consilience of their efforts—the way that data, theory and modelling back each other up. Doubters see this as a thoroughgoing version of “confirmation bias”, the tendency people have to select the evidence that agrees with their original outlook.
No one doubts that carbon dioxide is a greenhouse gas, good at absorbing infra-red radiation. It is also well established that human activity is putting more of it into the atmosphere than natural processes can currently remove. Measurements made since the 1950s show the level of carbon dioxide rising year on year, from 316 parts per million (ppm) in 1959 to 387ppm in 2009. Less direct records show that the rise began about 1750, and that the level was stable at around 280ppm for about 10,000 years before that. This fits with human history: in the middle of the 18th century people started to burn fossil fuels in order to power industrial machinery. Analysis of carbon isotopes, among other things, shows that the carbon dioxide from industry accounts for most of the build-up in the atmosphere.
Disagreement is not with the level of C02 or that it comes from human activity. It is with the warming associated with a particular level of CO2. Problems:
Background natural climate cycles.
Climate is a complex non-linear system
Oceans can absorb heat and add inertia to the climate system, so atmosphere warms more slowly than expected.
On the data front: There are three records of land-surface temperature put together from thermometer readings in common use by climatologists, one of which is compiled at the Climatic Research Unit of e-mail infamy. They all show warming, and, within academia, their reliability is widely accepted. Various industrious bloggers are not so convinced.
Pure theory says that doubling Co2 will result in 1 degree C of warming, which is not so problematic. "climate sensitivity". However there are feedback effects that can increase this. The most important involve water vapour and clouds. Warming air will absorb water vapour (powerful greenhouse gas) which is a positive feedback loop for warming. There is scientific uncertainity about how much the water vapour adds, one estimate is 1.7 degrees C, up from the 1 degree C above.
Another point of contention: greenhouse warming should cause warming down below and cooling in the stratosphere. Earlier observations did not corraborate this, but now evidence is building up in favour.
Clouds have both a cooling effect (reflecting sunlight from the upper atmosphere), as well as a greenhouse effect. Sorting these two out to get the net is complicated.
Another source of evidence is the climate of the past, like ice ages and the associated CO2 and other factors that contributed to it. The temperature records of the past millenium is one particular hotspot of debate. Tree rings is one source of data. A 1998 Nature article found a 'hockey stick' shape for temperatures of the last century, mostly flat but with the blip towards the end of the 20th century. This paper is widely contested by sceptics. One contestation is that this curve does not account for the 'medieval warm period' ; when, it is believed, temperatures were as warm or warmer than now.
The most accurate recent climate data cannot be used easily for checking the quality of models because of complexities like aerosols in the atmosphere whose effects are not known well enough so their effect is parameterized in the model instead of being strictly modelled. This also leads to accusations that they are parameterised in such a way as to make the models show higher levels of warming.
Wednesday, March 24, 2010
Saturday, March 13, 2010
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