The UnAustralian

Thursday, May 22, 2003
Atmospheric Carbon Dioxide Levels - Projected vs. Observed

The biggest problem with evaluating 110 year projections of future climate change, is that 110 years is a long time to wait and see. Fortunately, in the case of the IPCC SRES scenarios, they started running in 1990, so we have 13 years of data to look at. Unfortunately, 13 years out of 110 is bugger all, so and trends come and go unexpectedly, so any conclusions taken for these 13 years must be taken with a grain of salt. However, a bad assessment is better than no assessment at all, so here we go.

It is difficult to compare many climate and economic indicators as there are many different ways of collecting the data. For example, the IPCC measurement of total CO2 emissions includes land use. The IEA does not. The IPCC also has a different way of counting aviation related emissions, which leads to other differences.

There is however, one measurement which is pretty accurate. Atmospheric concentration of CO2 (and since GHG levels are what is important, it's a pretty significant measurement). Some of the best measurements of atmospheric CO2 are taken at Mauna Loa in Hawaii. In 2001 the atmospheric CO2 levels were 370.9 ppmv.

Other measurements around the world include Barrow in Alaska (372.3 ppmv), American Samoa (369.8 ppmv), and the South Pole (368.1 ppmv). All of these numbers are from 2001

Meanwhile, the various IPCC predictions fell into the 368 to 369 ppmv range, for the year 2000. Because the IPCC predictions are from 2000, whereas the observations are from 2001, it is necessary to add between 1.2 and 1.5 ppmv (these rates of change are taken from the observed values).

Sources: Carbon Dioxide Information Analysis Center
Climate Change 2001: The Scientific Basis
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