Post by kaima on Jul 28, 2006 18:54:45 GMT -7
I have had some initial luck at Googling for "800,000 year ice " and "800,000 year ice core" and suggest you all might try the same. I have not yet located all of the data I was presented at an engineering & science conference I attended, but essentially the scientific (not political) results from testing the trapped atmospheric gasses brought me over to believe in Global Warming about 3 or 4 years ago - which I consider rather recent in the argument.
In a picture, it is approximately
from www.sciencepoles.org/index.php?s=2&rs=home&uid=650&lg=en
"Sciencepoles talked, on 23 March, to Dominique Raynaud, from France's Laboratoire de Glaciologie et Géophysique de l'Environnement, who has worked for some time on understanding the "story of the ice" - what the ice cores extracted in recent years from the polar ice are telling us about the planet's climate history. He is coordinating the EU EPICA-MIS (European Project for Ice Coring in Antarctica - Marine Isotopic Stage) project devoted to paleoreconstruction and integrated climate analysis through marine and ice core studies. He is a lead author for the chapter on paleoclimate in the upcoming Fourth Assessment Report of the InterGovernmental Panel on Climate Change (IPCC) - due for release next year and which will represent a new benchmark for our understanding of climate change.
Dr. Raynaud is collaborating with Belgian researchers in Louvain-la-Neuve and elsewhere in Belgium in deciphering the critical climate evidence emerging from analysis of the ancient air trapped in ice, as well as cross-checking it against modelling approaches and against evidence obtained from deep sea sediments.
SciencePoles: Dr Raynaud, you've been involved for some time with deciphering what the Antarctic ice has to tell us. Previous ice cores from Antarctica have produced 400,000 years of evidence of a very strong relationship between greenhouse gas levels and global temperature - now you've examined even older ice. Is that telling us something new?
Doctor Raynaud (DR): It's important for people to remember that when we talk about the evidence of the ice, we're talking about the best possible means of preserving specimens of ancient atmosphere imaginable - modern science would have to work very hard to devise such a time capsule, a container that would preserve the air so well. So when we examine these ice cores, we're testing snow laid down eons ago - and the original air that surrounded the snowflakes is still trapped inside.
I've been involved for some time in the EPICA (European Project for Ice Coring in Antarctica) ice-core research. The ice-cores we've extracted from Antarctica take us back at least to eight hundred thousand years ago.
Previous ice-cores, extracted at Vostok in Antarctica, gave us four hundred thousand years of evidence. These demonstrated that average temperature and greenhouse gas levels were closely linked over four 100-thousand year cycles of glacials (ice ages) and interglacials. So far we've been able to confirm that story through the EPICA cores and unveil new data on the quarter of a million years before then (ie up to 650,000 years ago). What's interesting is that even though the character of the cycles over that quarter million year period are somewhat different - the interglacial periods are longer and not quite as warm - the strong correlation between temperature and greenhouse gases is still very clear. We don't expect it to be any different as we move further back in time to the 800,000 year mark.
SciencePoles: It's pretty clear how you go about measuring greenhouse gas levels - seeing as you have actual air from hundreds of thousands of years ago - but what about temperature? How do you asses that?
It is necessary to use proxy evidence to assess the global temperature over the corresponding periods. We do this by looking in particular at the isotopic composition of the ice which varies with the temperature of the snow at its formation site. This technique is often described as using a "paleothermometer".
The paleothermometer record tells us what was going on in the regional climate above where the ice formed, so we've got a pretty good picture of what was happening in Antarctica, as well as in Greenland. But when we cross-check the Antarctic record against other paleo records, such as marine sediments, you see that changes in temperature were happening globally, although to different degrees. The temperature changes closer to the poles are significantly larger than those at lower latitudes. Sometimes tens of degrees Celsius are involved.
SciencePoles: Is it shifts in the planet's orbit and corresponding shifts in the amount of energy reaching us from the sun (insolation) that causes an ice age to end or begin?
This is the curious thing. The shifts in energy input from orbital variation are small but they act as triggers. They are not the main drivers, but they are the initial drivers. These small increases or decreases in energy input to the earth's climate system seem to set in motion a range of complex feedback processes, some self-reinforcing (known as "positive feedback") and some self-extinguishing (or "negative feedback").
The positive feedback processes are much more powerful than the negative ones, which is why we see very large cyclical swings in temperature (global average of around 5-7 degrees Celsius between glacial maxima and interglacials) occurring. There is now a strong consensus among climate scientists that there are two major factors that contribute most to this "amplification" of the slight increases or decreases in the earth's exposure to the sun's power. The two key factors are consequent changes to atmospheric greenhouse gas levels and to the extent of ice coverage at the poles, especially in the North. The extent of vegetation across the planet and the levels of dust in the atmosphere are additional players.
In a warming phase, the heating of the globe leads to a decrease in annual ice coverage, which decreases the poles' reflectiveness, which in turn absorbs more heat, setting in train a "positive feedback loop". The level of greenhouse gases in the atmosphere is also increased by a slightly warming world (in particular the ocean becomes a source of atmospheric CO2 and permafrost retreats, releasing stored methane), which then leads to a still warmer world and so on until a stable, much warmer, climate is ultimately reached. All of this applies in reverse when the solar input decreases slightly at the other end of the cycle, taking the world back into an ice age.
Aren't clouds, which cover a much greater area of the earth's surface, more important in determining the earth's temperature? Aren't they an important part of the greenhouse effect and also reflect the sun's energy?
Yes, indeed they are important. In fact in a warming world they are one of the feedbacks that we are not yet able to understand well, with some competing effects: some clouds are contributing to the warming while others are cooling the atmosphere.
The retreat of the polar ice is where we are seeing major change, to a large degree as a result of human-induced changes to the levels of greenhouse gases.
Humankind is now heading towards a doubling of the CO2 level which was present in the atmosphere prior to the industrial revolution. The changes are small in terms of energy, a little like the orbital forcing inputs that set in train shifts in and out of ice ages, but they will entail all sorts of consequences: some predictable, others less so. What we are confident of is that the overall global temperature will increase by from 1.5 to 6 degrees by the end of the 21st century. By way of comparison the change in global average temperatures when we moved out of the last ice age was between 5 and 7 degrees. Only then it took around 10,000 years to do so. Now we're looking at compelling the planet to do it in a couple of centuries.
Would you agree with the description, by New York Times journalist Elizabeth Kolbert, that this represents "a vast uncontrolled experiment on the planet"?
I think we have to hope that it can be brought under control."
_ _ _
There are much better presentations of the analysis out there as well.
In a picture, it is approximately
from www.sciencepoles.org/index.php?s=2&rs=home&uid=650&lg=en
"Sciencepoles talked, on 23 March, to Dominique Raynaud, from France's Laboratoire de Glaciologie et Géophysique de l'Environnement, who has worked for some time on understanding the "story of the ice" - what the ice cores extracted in recent years from the polar ice are telling us about the planet's climate history. He is coordinating the EU EPICA-MIS (European Project for Ice Coring in Antarctica - Marine Isotopic Stage) project devoted to paleoreconstruction and integrated climate analysis through marine and ice core studies. He is a lead author for the chapter on paleoclimate in the upcoming Fourth Assessment Report of the InterGovernmental Panel on Climate Change (IPCC) - due for release next year and which will represent a new benchmark for our understanding of climate change.
Dr. Raynaud is collaborating with Belgian researchers in Louvain-la-Neuve and elsewhere in Belgium in deciphering the critical climate evidence emerging from analysis of the ancient air trapped in ice, as well as cross-checking it against modelling approaches and against evidence obtained from deep sea sediments.
SciencePoles: Dr Raynaud, you've been involved for some time with deciphering what the Antarctic ice has to tell us. Previous ice cores from Antarctica have produced 400,000 years of evidence of a very strong relationship between greenhouse gas levels and global temperature - now you've examined even older ice. Is that telling us something new?
Doctor Raynaud (DR): It's important for people to remember that when we talk about the evidence of the ice, we're talking about the best possible means of preserving specimens of ancient atmosphere imaginable - modern science would have to work very hard to devise such a time capsule, a container that would preserve the air so well. So when we examine these ice cores, we're testing snow laid down eons ago - and the original air that surrounded the snowflakes is still trapped inside.
I've been involved for some time in the EPICA (European Project for Ice Coring in Antarctica) ice-core research. The ice-cores we've extracted from Antarctica take us back at least to eight hundred thousand years ago.
Previous ice-cores, extracted at Vostok in Antarctica, gave us four hundred thousand years of evidence. These demonstrated that average temperature and greenhouse gas levels were closely linked over four 100-thousand year cycles of glacials (ice ages) and interglacials. So far we've been able to confirm that story through the EPICA cores and unveil new data on the quarter of a million years before then (ie up to 650,000 years ago). What's interesting is that even though the character of the cycles over that quarter million year period are somewhat different - the interglacial periods are longer and not quite as warm - the strong correlation between temperature and greenhouse gases is still very clear. We don't expect it to be any different as we move further back in time to the 800,000 year mark.
SciencePoles: It's pretty clear how you go about measuring greenhouse gas levels - seeing as you have actual air from hundreds of thousands of years ago - but what about temperature? How do you asses that?
It is necessary to use proxy evidence to assess the global temperature over the corresponding periods. We do this by looking in particular at the isotopic composition of the ice which varies with the temperature of the snow at its formation site. This technique is often described as using a "paleothermometer".
The paleothermometer record tells us what was going on in the regional climate above where the ice formed, so we've got a pretty good picture of what was happening in Antarctica, as well as in Greenland. But when we cross-check the Antarctic record against other paleo records, such as marine sediments, you see that changes in temperature were happening globally, although to different degrees. The temperature changes closer to the poles are significantly larger than those at lower latitudes. Sometimes tens of degrees Celsius are involved.
SciencePoles: Is it shifts in the planet's orbit and corresponding shifts in the amount of energy reaching us from the sun (insolation) that causes an ice age to end or begin?
This is the curious thing. The shifts in energy input from orbital variation are small but they act as triggers. They are not the main drivers, but they are the initial drivers. These small increases or decreases in energy input to the earth's climate system seem to set in motion a range of complex feedback processes, some self-reinforcing (known as "positive feedback") and some self-extinguishing (or "negative feedback").
The positive feedback processes are much more powerful than the negative ones, which is why we see very large cyclical swings in temperature (global average of around 5-7 degrees Celsius between glacial maxima and interglacials) occurring. There is now a strong consensus among climate scientists that there are two major factors that contribute most to this "amplification" of the slight increases or decreases in the earth's exposure to the sun's power. The two key factors are consequent changes to atmospheric greenhouse gas levels and to the extent of ice coverage at the poles, especially in the North. The extent of vegetation across the planet and the levels of dust in the atmosphere are additional players.
In a warming phase, the heating of the globe leads to a decrease in annual ice coverage, which decreases the poles' reflectiveness, which in turn absorbs more heat, setting in train a "positive feedback loop". The level of greenhouse gases in the atmosphere is also increased by a slightly warming world (in particular the ocean becomes a source of atmospheric CO2 and permafrost retreats, releasing stored methane), which then leads to a still warmer world and so on until a stable, much warmer, climate is ultimately reached. All of this applies in reverse when the solar input decreases slightly at the other end of the cycle, taking the world back into an ice age.
Aren't clouds, which cover a much greater area of the earth's surface, more important in determining the earth's temperature? Aren't they an important part of the greenhouse effect and also reflect the sun's energy?
Yes, indeed they are important. In fact in a warming world they are one of the feedbacks that we are not yet able to understand well, with some competing effects: some clouds are contributing to the warming while others are cooling the atmosphere.
The retreat of the polar ice is where we are seeing major change, to a large degree as a result of human-induced changes to the levels of greenhouse gases.
Humankind is now heading towards a doubling of the CO2 level which was present in the atmosphere prior to the industrial revolution. The changes are small in terms of energy, a little like the orbital forcing inputs that set in train shifts in and out of ice ages, but they will entail all sorts of consequences: some predictable, others less so. What we are confident of is that the overall global temperature will increase by from 1.5 to 6 degrees by the end of the 21st century. By way of comparison the change in global average temperatures when we moved out of the last ice age was between 5 and 7 degrees. Only then it took around 10,000 years to do so. Now we're looking at compelling the planet to do it in a couple of centuries.
Would you agree with the description, by New York Times journalist Elizabeth Kolbert, that this represents "a vast uncontrolled experiment on the planet"?
I think we have to hope that it can be brought under control."
_ _ _
There are much better presentations of the analysis out there as well.