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New Antarctic Ice Core Data: A Closer Look
These additional graphs of the ice core data were made on May Day, 2000.
This page was last updated on May 30, 2000.
The previous web page shows ice core data for temperature variability and CO2 concentration over the past 420,000 years. Because of the large time scale, the details of how temperature and CO2 have changed in more recent times are not apparent. The graphs on this page are of the same data, but with progressively smaller time scales in order to show those changes. The ranges in temperature variation and CO2 concentration have also been narrowed to highlight changes.
The first graph (Data 2) on this page is for the past 18,000 years. This time period roughly corresponds to the time since the last glacial maximum, that is, when temperatures and CO2 concentrations were lowest. It shows how temperatures and CO2 levels then rose, reached a plateau at the beginning of the present Holocene interglacial phase, and then rose again to above +2C over the plateau around 8,000 years ago. These brief high temperatures triggered a short relapse of colder conditions for about 200 years, but were evidently not hot enough or long enough to trigger another glacial phase. 
This relapse was more pronounced in the northern hemisphere, as was another glacial relapse known as the Younger Dryas around 11,000 BP. It seems the northern hemisphere is affected more by global temperature changes than the southern hemisphere. This could be explained by the fact that the North Polar sea ice is much thinner and much less extensive than the South Polar continental ice, and is therefore much more susceptible to melting under warm conditions, thereby precipitating shifts or shutdowns in the thermohaline circulation. The mass of North Polar sea ice has thinned by at least 50% in just the past 30 years.
The second graph (Data 3) is for the past 200 years. This time period includes all of the Industrial Revolution which began in the mid-1800s. The start of the Industrial Revolution marked the beginning of the large-scale exploitation of fossil fuels. The small dip in temperature in the early 1800s was caused by volcanic eruptions which reduced the amount of sunlight reaching the Earth’s surface. CO2 inflection points are visible at around 1860, 1950 and 1975. After 1958, the data are from annual air measurements, not ice core proxies, and are therefore of higher quality. 
The third graph (Data 4) illustrates the most recent data set of actual air measurements. It shows how temperatures and CO2 concentrations have increased in recent times. A linear trend line fitted to the temperature data would indicate that the critical +2C level would be reached in about 40 years. But we don’t know that the trend is linear. Recent research indicates that it is probably exponential. Or it may be that peak temperatures are more important than mean temperatures. In either of these cases the +2C threshold would be reached much sooner.
As Wallace Broecker likes to say, the Earth’s climate system is “an angry beast” and one that we should not be poking with sticks, which of course is exactly what we are doing with all our carbon dioxide and other GTG emissions. We don’t know exactly when or how “the beast” will react, but we do know that it eventually will. It’s not a matter of whether, it’s only a matter of when and how. Those of us who live in geographcal regions affected by the North Atlantic thermohaline circulation should be especially aware of how sensitive this part of “the beast’s” anatomy is to poking and prodding.
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