Recent Record Growth in Atmospheric CO2 Levels
Roger J. FranceyCSIRO Atmospheric Research, Melbourne VIC 3195, Australia. Email: roger.francey@csiro.au
Roger Francey is a Post-Retirement Fellow at CSIRO Atmospheric Research. He shared, with Paul Steele, the 2001 Victoria Prize for ‘ground-breaking work to improve ways to measure greenhouse gases’. He is an advisor to the Max-Planck Institute for Biogeochemistry and to the flagship European Commission CarboEurope program. |
Environmental Chemistry 2(1) 3-5 https://doi.org/10.1071/EN05013
Submitted: 10 February 2005 Accepted: 18 February 2005 Published: 21 March 2005
Environmental Context. Excessive levels of carbon dioxide are accumulating in the atmosphere, principally from burning fossil fuels. The gas is linked to the enhanced greenhouse effect and climate change, and is thus monitored carefully, along with other trace gases that reflect human activity.The rate of growth of carbon dioxide has increased gradually over the past century, and more rapidly in the last decade. Teasing out fossil emissions from changes due to wildfires and to natural exchange with plants and oceans guide global attempts in reducing emissions.
[1]
C. M. Trudinger,
I. G. Enting,
P. J. Rayner,
R. J. Francey,
J. Geophysical Research 2002, 107, D20 4423.
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* The mixing ratio of CO2 in dry air is given in units of ppm or μmol mol–1. The rate of growth, around 1.4 ppm yr–1 (0.36% yr–1) through the 1990s, has been around 2 ppm yr–1 or more (0.53% yr–1) since 2001.
† Measurements are made at Gaslab, CSIRO Atmospheric Research. Samples collection relies on direct and/or in-kind support, particularly from the Bureau of Meteorology, Antarctic Division, and Institute of Marine Science (Australia), NOAA and Scripps Institute of Oceanography (USA), Environment Canada, and Centre for Ecology & Hydrology (UK).
‡ ENSO stands for El Niño–Southern Oscillation. El Niño describes the quasi-periodic ocean upwelling in the tropical east Pacific, and Southern Oscillation describes the climatically linked pressure gradient between Tahiti and Darwin.
§ Allowing at least six months for the atmosphere to mix globally. The growth rates at Cape Grim, north-west Tasmania (selected for winds off the Southern Ocean), Macquarie Island, and the Antarctic sites Mawson, Casey, and South Pole are remarkably consistent. Note that the small differences that do exist between these sites, if measured precisely, assume considerable significance in detecting possible slow changes in the crucial ability of the Southern Ocean to absorb CO2.
¶ Gt stands for giga (109, sometimes billion) tonnes. Current fossil fuel emissions are ~26 Gt CO2 or ~7 Gt C (carbon) per year. A 0.471 ppm global CO2 increase corresponds to an extra 1 Gt C (3.7 billion tonnes of CO2).
║ This period also includes the 1991 volcanic explosion at Pinatubo, the Phillipines. It is also interesting that the previous extended El Niño during the 1940s also showed low CO2 growth based on the reconstruction of atmospheric CO2 from Antarctic ice cores.[1]
** The atmospheric variations observed in stable CO2 isotopes predominantly involve carbon that has experienced fractionation during CO2 photosynthesis by land plants (which includes the fossil plants comprising fossil fuels). The longer the timescale of the atmospheric variations, the more the original isotopic labelling by terrestrial photosynthesis is diluted, mainly by exchange with the large reservoirs of oceanic carbon. Monitoring of 14CO2 that distinguishes fossil from modern plant sources is, unfortunately, not yet widely available.
†† The extended conflagration of 600 oil wells in the 1991 Gulf War represented only about 1% of global industrial emissions and were not detected in the global CO2 growth rates.
‡‡ Atmospheric lifetimes are: for CO, 20 days in the tropics, >100 days at high latitude; for H2, ~2 years; for CH4, ~11 years; and for CO2 ~100 years.
§§ For example, with relatively low Cape Grim CO growth in 2002 explained by tropical fires in the more distant Amazon, compared to the 1997–1998 Indonesian event, and in 2003 by fires in Siberia.
