Here is a neat little animation that illustrates the time history of atmospheric carbon dioxide (CO2) from 800,000 years ago until January, 2011.
The animation begins with the CO2 variability (based on direct measurements from key observation sites) from January 1979 until January 2011. There are several patterns that are worth noting, firstly the relentless upward trend of the globally averaged carbon dioxide concentration beginning in January 1979 at 336 ppm (parts per million) and ending with a concentration of 391 ppm, the average in January 2011. Strong inter-annual variability are also evident, particularly in the northern hemisphere – we are essentially seeing the Earth’s breathing pattern! Fluctuations follow the growing season, peaking in spring with widespread plant greening and minimizing in autumn when biomass is greatest. During the growing season photosynthesizing plants suck up CO2 whereas during the colder part of the year respiration dominates – plants and animals exhale CO2. As shown on the graph these fluctuations are far greater in the northern hemisphere than the southern hemisphere (where land area and vegetation cover is much smaller in comparison).
To go back further in time from the preindustrial era to 800,000 years ago requires the careful analyse of ancient air trapped in ice-cores drilled from Greenland and Antarctica. (Blog posts on detecting past climate information from ice-cores can be read here and here). Long timescale variability reveals cycles of ~41000 years and ~100000 years, which mark the intervals of glaciations.
Finally, the data clearly shows that current concentrations of atmospheric carbon dioxide are at levels not seen in the last 800 thousand years (and actually most likely not even the past 20 million years). This rapid rise of atmospheric CO2 to such heightened levels is worrying for our planet and those who (will) live on it.