The inconvenient truth about the Ice core Carbon Dioxide Temperature Correlations | ScienceBits
This page introduces Antarctic ice-core records of carbon dioxide (CO2) that now the CO2 ratio is calculated as the ratio of the CO2 peak to the air (O2 + N2) peak. , Climate and Atmospheric History of the Past , years from the. May 27, To quote, he says the following when discussing the ice-core data (about 40 “ The relationship is actually very complicated but there is one relationship When there is more carbon dioxide, the temperature gets warmer. Dec 3, At least three careful ice core studies have shown that CO2 starts to rise The correlation between CO2 and temperature in the pre-industrial.
Such an example is found in the figure below. There are many examples of studies finding lags, a few examples include: Science, volp. Science vol, find that the start of the CO2 increase in the beginning of the last interglacial lagged the start of the temperature increase by years.
Clearly, the correlation and lags unequivocally demonstrate that the temperature drives changes in the atmospheric CO2 content. The same correlations, however cannot be used to say anything about the temperature's sensitivity to variations in the CO2. I am sure there is some effect in that direction, but to empirically demonstrate it, one needs a correlation between the temperature and CO2 variations, which do not originate from temperature variations.
The only temperature independent CO2 variations I know of are those of anthropogenic sources, i. Since the increase of CO2 over the 20th is monotonic, and other climate drivers e.
Ice core basics
This "random walk" in the amount of CO2 is the reason why there were periods with 3 or even 10 times as much CO2 than present, over the past billion years. Unfortunately, there is no clear correlation between CO2 and temperature over geological time scales. More about it in this paper. The moral of this story is that when you are shown data such as the graph by Al Gore, ask yourself what does it really mean.
You might be surprised from the answer. Upper limit on the effects of CO2 It turns out that the CO2 temperature correlation can be used to say one thing about the temperature effects of CO2 variations. It can be used to place an upper limit on the temperature sensitivity to CO2. The reason is that if CO2 has a large effect, the positive feedback from any temperature change would drive an additional temperature change which could render the climate system unstable, something which luckily isn't the case.
We can calculate this critical feedback relatively easily, and thus place an upper limit on the temperature sensitivity. Per unit temperature change, it is: This statement does not tell the whole story. In the case of warming, the lag between temperature and CO2 is explained as follows: In turn, this release amplifies the warming trend, leading to yet more CO2 being released.
In other words, increasing CO2 levels become both the cause and effect of further warming. This positive feedback is necessary to trigger the shifts between glacials and interglacials as the effect of orbital changes is too weak to cause such variation. Additional positive feedbacks which play an important role in this process include other greenhouse gases, and changes in ice sheet cover and vegetation patterns.
A study by Shakun et al. Disparate records often provide conflicting evidence. This ice core attempted to investigate the evidence for cooler temperatures during this period. The top 50 m of the ice core was analysed at 2.
Ice Core Data Help Solve a Global Warming Mystery - Scientific American
Ice core samples were analysed for stable isotope ratios, major ions and trace elements. An age model was extrapolated to the ice core using a firm decompaction model. The study showed that there were three distinct periods: The area was cooler and stormier. The ice core is continuously melted and analysed by numerous automatic machines. The most important property of ice cores is that they are a direct archive of past atmospheric gasses.
Air is trapped at the base of the firn layer, and when the compacted snow turns to ice, the air is trapped in bubbles.
Ice Core Data Help Solve a Global Warming Mystery
This transition normally occurs m below the surface. The offset between the age of the air and the age of the ice is accounted for with well-understood models of firn densification and gas trapping. The air bubbles are extracted by melting, crushing or grating the ice in a vacuum. This method provides detailed records of carbon dioxide, methane and nitrous oxide going back overyears.
Ice core records globally agree on these levels, and they match instrumented measurements from the s onwards, confirming their reliability. Carbon dioxide measurements from older ice in Greenland is less reliable, as meltwater layers have elevated carbon dioxide CO2 is highly soluble in water.
Older records of carbon dioxide are therefore best taken from Antarctic ice cores. Other complexities in ice core science include thermal diffusion. Prior to becoming trapped in ice, air diffuses to the surface and back.
There are two important fractionation processes: Thermal diffusion occurs if the surface is warmer or colder than the bottom boundary the close-off depth. This temperature gradient occurs from climate change, which affects the surface first. The heavier components of the air like stable isotopes also tend to settle down gravitational settling. Thermal diffusion and gravitational settling can be measured and analysed because the fractionation of air follows well understood principles and relationships between different stable isotopes namely, nitrogen and argon.
Other gasses Other major gases trapped in ice cores O2, N2 and Ar are also interesting. Other ice-core uses The vertical profile of an ice core gives information on the past surface temperature at that location.
In Greenland, glass shard layers from volcanic eruptions tephra are preserved in ice cores. The tephra ejected in each volcanic eruption has a unique geochemical signature, and large eruptions projecting tephra high into the atmosphere results in a very wide distribution of ash.
These tephra layers are therefore independent maker horizons; geochemically identical tephra in two different ice cores indicate a time-synchronous event. They both relate to a single volcanic eruption.