The level of the major greenhouse gas, carbon dioxide, in the Earth鈥檚 atmosphere has hit a record high, US government scientists have reported.
The new data from the US National Oceanic and Atmospheric Administration also suggest that the rate of increase of the gas may have accelerated in the last two years. Carbon dioxide emissions, mainly from burning fossil fuels, are thought to be a principle cause of global warming.
Recordings from a volcano-top observatory, NOAA鈥檚 Mauna Loa Observatory on Hawaii, showed carbon dioxide levels had risen to an average of about 376 parts per million (ppm) for 2003.
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This is 2.5 ppm up from the average for 2002. It is not the highest leap in year-on-year atmospheric carbon dioxide levels recorded by NOAA. But it is the first to be sustained, with 2002 levels up 2.5 ppm from 2001.
This year-on-year hike is considerably larger than the average annual increase of about 1.5 ppm seen over the last few decades says Pieter Tans, chief scientist at NOAA鈥檚 climate monitoring and diagnostic lab in Boulder, Colorado, US. Other NOAA scientists suggest that economic development in China and India, which leads to increased fuel use, could be a key factor.
Year on year
鈥淲e have been increasing our emissions of greenhouse gases since 1990 and this acceleration is something that we have been aware of and expected,鈥� says David Viner, a climate change expert at the University of East Anglia, UK.
鈥淚t鈥檚 going to continue to cause profound changes in the climatic system,鈥� he told 麻豆传媒. 鈥淲e are almost already seeing year on year increases in global temperatures.鈥�
But Brian Hoskins, a member of the UK鈥檚 Royal Commission on Environmental Pollution, which advises the government, warns that it is not possible to conclude that the rise in carbon dioxide levels has quickened its pace from just one year鈥檚 figures.
鈥淥ne swallow does not make a summer,鈥� he told 麻豆传媒. 鈥淲e know how much carbon dioxide we are producing and it hasn鈥檛 changed suddenly over the last year.鈥�
Tans agrees: 鈥淚 would be cautious at this point to interpret too much. Yes it鈥檚 certainly the highest increase in any two-year period we have seen. But to draw conclusions that now we are really into a new trend 鈥� that鈥檚 too early.鈥�
However, he adds: 鈥淭hings are steadily going up. Every single month is a new record. I鈥檓 not surprised that carbon dioxide levels continue to go up because fossil fuel burning also continues to go up,鈥� he told 麻豆传媒.
Charles Keeling at the Scripps Institution of Oceanography in San Diego, US, notes that global warming itself could increase the amount of carbon dioxide released from the oceans and soil. 鈥淧eople are worried about feedbacks,鈥� he says.
Inexorable rise
When the US team started recording atmospheric carbon dioxide in the late 1950s, levels were around 315 ppm and have risen ever since.
The Intergovernmental Panel on Climate Change projects that, if unchecked, carbon dioxide concentrations in the atmosphere will have risen to between 650 and 970 ppm by 2100. As a result, global temperatures would warm by nearly 6掳C compared with 1990 levels, the IPCC predicts.
However, moves to implement the Kyoto Protocol aimed at cutting greenhouse gas emissions have stalled as the US has refused to ratify it, and Russia has not yet made a decision.
鈥淭his [record level] really shows the importance of the international community tackling climate change,鈥� says Viner. 鈥淐limate change has stuck its head above the parapet 鈥� it鈥檚 not an issue politicians can hide from much longer.鈥�
