I previously did a research project on polar ice cores at my college and I just want to share some parts of this here, as it relates to correlation between global warming and greenhouse gases.
Continue below the fold...
Just to familiarize everyone with what polar ice cores are, some basic information:
Ice cores are cylinders of ice, removed from an ice sheet or glacier by drilling into the polar ice caps, located in places like Antarctica and Greenland, where temperatures remain below freezing year around.
Because snow cannot melt in these environments, each year’s snowfall accumulates on top of previous year’s snowfalls. Over a long period of time, these snowfalls form layers of ice deep down. Some polar ice cores, such as one in Vostok, Antarctica, are as deep as 2000 meters.
Ice cores contain an abundance of information about past climatic periods, as discussed here.
When snow falls it carries with it the compounds that are in the air at the time, compounds ranging from sulfate, nitrate and other ions, to dust, radioactive fallout, and trace metals. When snow falls in a place where temperatures above freezing are rare (there is only a hint of any melting at the GISP2 site in the 750 year record recovered to date), such as in polar regions or at high altitude, the snow from one year falls on top of the previous year without melting.
Included in these records are evidence in any given year for the temperature, ocean volume, precipitation, methane totals, greenhouse gas totals, solar variability, sea-surface productivity, and gas composition of the atmosphere. The cores also show records for volcanic eruptions, desert extent, and forest fires.
By drilling at greater and greater depths and analyzing the ice, a timeline can be established for the history of the core and the history of the climate that was left in the core. In some cases, polar ice cores have left climatic records of up to 500,000 years.
Information on collection of the core can be found here.
Determining the Timeline of Events
The recent history is much easier to date, since individual layers may be counted, each layer representing a year. The process for calculating the layers involves visibly looking at them, chemically examining them, and looking at the isotopes. Once at greater depths, the core layers become thinner. At this point, a time frame is given by using rate variations and ice flow.
Inside the Ice
A long with the snowfall, everything that is in the air at the time of the snow is also buried. This may include dust, radioactive material, ash, trace metals, atmospheric gases, and ions such as sulfate and nitrate. Thus when climatic events such as volcanic eruptions or meteorite showers occur, evidence is left in the snow in the form of ash, particles, and isotopes.
Volcanic Eruptions and Other Findings
One area where the ice cores can be used is to determine past volcanic eruptions, as discussed here.
Volcanoes can produce large quantities of particles and leave a record in the ice. Scanning electron micrographs of the particles from a particularly large dust peak in an ice core may reveal that it is from a known volcano and allow a firm date to be placed on that section of core. For prehistoric times, the dust record is a key tool for reconstructing a history of volcanic activity.
The dusts records help establish a history for volcanic eruptions since volcanoes leave a large quantity of particles in the ice, such as ash, sulfate, and chloride when they erupt. Thus, there will be visible ash layers in the ice, indicating any volcanic eruptions. By analyzing one of these large dust peaks in the ice with an electron micrograph scan, the source of the eruption may be indicated and a timeline of the event can be established.
One case here was a volcanic eruption in Oraefajokull, Iceland. With the use of electrical conductivity measurements, it was determined that a volcanic eruption originated from in the area in 1362 A.D. Large peaks in dust particles from the ice were analyzed and identified as volcanic ash by evidence of morphology and chemical composition. By using the timeline methods mentioned earlier, scientists were able to assign a date.
Other findings include metheor strikes, solar strength, conclusions of glacial advances, sea level variations, and of course global warming caused by increases in greenhouse gases.
Global Warming
Besides volcanoes and the other indicators, there appears to be a correlation between temperature and greenhouse gas levels, as indicated by research at Vostok. Interglacial periods (periods of warming), for example, are correlated with findings of high levels of CO2 and CH4 (greenhouse gases) in the ice. Meanwhile periods of cooling are indicated with low levels of CO2 and CH4 in the ice.
The first and third graphs above are CO2 and CH4 levels, while the middle one is the change in temperature. The more recent years are on the left. As you can, there is almost exact correlation in those graphs between the greenhouse gas levels and temperature.
Now how does this relate to global warming today?
Research at the Vostok ice core has shown current CO2 levels to be the highest in the history of the core, due to the increased burning of fossil fuels. If the global climate of the past is used as an indicator, higher temperatures and an interglacial, warming period would be predicted for the future. As we are seeing today, in fact temperatures are increasing, a long with the CO2 levels in the core.
Here is another graph, showing more clearly the recent increases in CO2, being caused mostly by humans. At the end, there is a very rapid increase.
So there you have it, the record is all in the ice. And if we look at the past in the cores from these graphs, it would seem the warming period is going to be followed by extreme cooling, as some scientists have predicted.
Basically what polar ice cores are showing us is that there is a correlation between higher temperatures and increases in greenhouse gases. Once again, we have come to a period of high presence of greenhouse gases and research at Vostok is showing that it has been caused by a large part from human causes, such as the burning of fossil fuels.