A potential fallacy in ice core studies?

A thought about ice cores just occurred to me, and I need someone in the know to verify or refute this argument.

Scientists claim to know what the temperature was in past years primarily by drilling ice core samples. They measure levels of specific gasses, like carbon dioxide, that are trapped within the layers of the ice, and somehow they calculate the temperature for that time based off of "certain assumptions" (none of which are mentioned in the wikipedia article). That is rather dubious inandof itself, but I want to take that thought in a different direction.

We all know that it was warmer at times in the past than it was today. We also know that glaciers melted, species became extinct due to climate changes and violent hurricanes stuck the mouth of the Mississippi River long before we ever got here. However, the environmentalists cite the ice core temperature data to claim that things are worse today because we are increase the Earth’s temperature at an unprecedented rate.

However, even in a super compacted state, like deep within a glacier, ice is still relatively porous and open to gas diffusion. At the depths layers from 50k-100k+ years ago are found, the pressure of the ice's own weight prevents any rapid movement of gas, but the prevailing physical law that everything moves from areas of higher concentration to lower concentration holds true. Consequently, even if the diffusion rate is very, very slow, there will be some amount of gas diffusion between ice layers.

As a result, the further back in time we go, the more gasses used to measure the temperature of the atmosphere will have diffused between layers. The diffusion rate would likely be slow enough that the temperature calculation could be accepted as fact, assuming their assumptions are true. However, in the event of a rapid increase or decrease in temperature, the concentration levels would vary greatly between nearby layers, and so the gas would diffuse to a greater extent. Unless you find a sufficiently accurate means to account for this, the resultant temperature change would appear to happen much slower than what actually occurred.

So that calls into question all ice core data, especially in relation to the assertion that humans are causing unprecedented warming. Not that global warming has much to do with actual science, but generally the people involved are trying to be scientifically accurate in their own way.

This may be something the calculations already take into account or one of the unspoken "certain assumptions", but given what I know about chemistry and ice, this makes sense to me. Is there a chemist, a mineralogist or an atmospheric physicist in the house? (Did you hear about when they want to a bar? The mineralogist fell into the chemist, and they both evaporated into the atmospheric physicist.)

I know nothing about ice cores and temperature measurement, but a quick google turned up this NASA link which you might find interesting:

Paleoclimatology The Ice Core Record

The relevant bit seems to be this:

"As with marine fossils, the ratio of oxygen isotopes in the snow reveals temperature, though in this case, the ratio tells how cold the air was at the time the snow fell. In snow, colder temperatures result in higher concentrations of light oxygen."

There is another article on the subject of oxygen isotopes:

Paleoclimatology The Oxygen Balance

Okay, so they use the oxygen isotope ratio in the snow to reveal the temperature, which makes sense, and look at the levels of dissolved gasses within ice layers to get a picture of the atmosphere at that moment in time. Diffusion would still throw off results, and unless they account for this, they have a significant error to deal with as they attempt to relate that atmosphere to today. Furthermore, as the ice compacts, the layers become indistinguishable which means there is probably some exchange of oxygen isotopes between layers, not to mention what would occur as the ice very slowly flows over 100,000 years or if there was a period of warming that melted some layers away.

I'll have to read more about this, but something about ice core drilling never seemed right to me.

///@\\\

Short answer, I dunno. The same thought has crossed my mind. I would like to know about all the traces found in these ice cores, with a view of perhaps finding junk suggestive of bolide impacts and whatnot. Iridium was found in a layer laid down in Antarctica (if memory serves, and it sometimes doesn't, so I'll go look later) by the Eltanin impact 2 million years ago. And traces of an Alaskan volcano's eruption was found in one of the Greenland cores, although it was (of course) first attributed to the (IMHO fictional) mid-2nd millennium BC eruption of Thera.

Identification of Aniakchak (Alaska) tephra
in Greenland ice core
challenges the 1645 BC date
for Minoan eruption of Santorini
Nicholas J. G. Pearce
John A. Westgate and Shari J. Preece
Warren J. Eastwood
William T. Perkins
Minute shards of volcanic glass recovered from the 1645 ± 4 BC layer in the Greenland GRIP ice core have recently been claimed to originate from the Minoan eruption of Santorini [Hammer et al., 2003]. This is a significant claim because a precise age for the Minoan eruption provides an important time constraint on the evolution of civilizations in the Eastern Mediterranean. There are however significant differences between the concentrations of SiO2, TiO2, MgO, Ba, Sr, Nb and LREE between the ice core glass and the Minoan eruption, such that they cannot be correlatives. New chemical analyses of tephra from the Late Holocene eruption of the Aniakchak Volcano in Alaska, however, show a remarkable similarity to the ice core glass for all elements, and this eruption is proposed as the most likely source of the glass in the GRIP ice core. This provides a precise date of 1645 BC for the eruption of Aniakchak and is the first firm identification of Alaskan tephra in the Greenland ice cores. The age of the Minoan eruption of Santorini, however, remains unresolved.

Oh, okay, it wasn't in the Antarctic ice, it was in ocean floor sediments.

Ocean splashdown
by Henry Gee
UC Davis Geology Department
An asteroid between one and four km in diameter that splashed into the Southern Ocean, 1500 km SW of Chile, just over two million years ago, may have worsened a period of global cooling that saw the emergence of modern humans... The impact in question was first discovered during a cruise of the Eltanin in the 1960s: betrayed by anomalously high amounts of iridium in ocean-bed cores... Gersonde and his colleagues have taken another look, their results coming from a cruise in 1995 by the research ship Polarstern. The impact left a distinctive 'signature' of geological layers, very like that of the Chicxulub impact. Lowest in the 'impact' sequence is a thick layer of disordered rubble, full of chunks of rock up to 50 cm across: this layer represents the large-scale disturbance immediately after the impact as the ten-megaton blast ripped up the ocean floor. This layer took around four hours to settle after the blast. Smaller particles, such as grains of sand, took longer to settle, explaining why this layer was found immediately above the rubble layer. Capping the whole sequence is a thin layer of very fine sediment, dispersed over a wide area. This would have contained fine-grained material (including vaporized asteroid) flung high into the air and which took days or months to settle out. This layer contained the iridium.

Ice core data is valid when making a comparison between different gases present. The Vostok samples have proven cyclical movement of temperatures (derived from O¹⁸ isotope) that nearly coincide with cyclical movement of CO₂ levels.

The problem lies when alarmists mix Antarctic ice core data from tens of thousands of years ago with North American atmospheric data taken today. There is no scientific validity in mixing both data sets. Atmospheric levels will naturally be higher because of diffusivity.

As for the causal relationship of CO₂ levels and temperature levels throughout the cyclical patterns of the ice core data over the last 600,000 years, the evidence shows that changes in CO₂ levels actually trailed changes in temperature. Thus higher temperatures lead to higher CO₂ levels, and not the other way around.

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