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Cape Grim in Tasmania
Global average carbon dioxide concentrations rose by 0.8% during 2016, the largest annual increase ever observed, write researchers Paul Fraser, Paul Krummel and Zoe Loh of Australiaās national science agency CSIRO. Courtesy The Conversation.
According toĀ figures released overnight by the World Meteorological Organisation, atmospheric COā concentrations reached 403.3 parts per million. This is the highest level for at least 3 million years, having climbed by 3.3 ppm relative to the 2015 average.
The unprecedented rise is due to carbon dioxide emissions from fossil fuels (coal, oil and gas) and the strong 2015-16 El NiƱo event, which reduced the capacity of forests, grasslands and oceans to absorb carbon dioxide from the atmosphere.
Greenhouse gas levels are unprecedented in modern times.Ā WMO
The figures appear in the WMOās annualĀ Greenhouse Gas Bulletin. This is the authoritative source for tracking trends in greenhouse gases that, together with temperature-induced increases in atmospheric water vapour, are the major drivers of current climate change.
Laboratories around the world, including at CSIRO and the Bureau of Meteorology in Australia, measure atmospheric greenhouse gas concentrations at more than 120 locations. The gases include carbon dioxide, methane and nitrous oxide, as well as synthetic gases such as chlorofluorocarbons (CFCs).
AtĀ Cape GrimĀ in Tasmania, we observed a corresponding increase during 2016 of 3.2 ppm, also the highest ever observed.
For 2017 so far, Cape Grim has recorded a smaller increase of 1.9 ppm. This possibly reflects a reduced impact of El NiƱo on atmospheric carbon dioxide growth rates this year.
Long-term record of background carbon dioxide from Cape Grim, located at the northwest tip of Tasmania.Ā CSIRO/BoM
ForĀ roughly 800,000 yearsĀ before industrialisation began (in around the year 1750), carbon dioxide levels remained below 280 parts per million, as measured by air trapped in Antarctic ice.Ā Geological recordsĀ suggest that the last time atmospheric levels of carbon dioxide were similar to current levels was 3-5 million years ago. At that time, the climate was 2-3ā warmer than todayās average, and sea levels were 10 to 20 metres higher than current levels.
Human-driven change
The extraordinarily rapid accumulation of COā in the atmosphere over the past 150 years isĀ overwhelmingly and unequivocally due to human activity.
Methane is the second-most-important long-lived greenhouse gas in the atmosphere, with 40% coming from natural sources such as wetlands and termites andĀ the remaining 60% from human activitiesĀ including agriculture, fossil fuel use, landfills and biomass burning.
In 2016, global atmospheric methane also hit record levels, reaching 1,853 parts per billion, an increase of 9 ppb or 0.5% above 2015 levels. At Cape Grim, methane levels climbed by 6 ppb in 2016, or 0.3% above 2015 levels.
Nitrous oxide is the third-most-important greenhouse gas, of which [around 60% comes from natural sources such as oceans and soils], andĀ 40% from fertilisers, industrial processes and biomass burning.
In 2016, global atmospheric nitrous oxide hit a record 328.9 ppb, having climbed by 0.8 ppb (0.2%) above 2015 levels. At Cape Grim, we observed the same annual increase of 0.8 ppb.
If we represent the climate change impact of all greenhouse gases in terms of the equivalent amount of COā, then this āCOā-eā concentration in the atmosphere in 2016 would be 489 ppm. This is fast approaching the symbolic milestone of 500 ppm.
These record greenhouse gas levels are consistent with the observed rise in global average temperatures, which also hitĀ record levels in 2016.
The only way to reduce the impact is to significantly reduce our greenhouse gas emissions. TheĀ Kyoto ProtocolĀ and the subsequentĀ Paris AgreementĀ are important first steps in a long and challenging process to reduce such emissions. Their immediate success and ultimate strengthening will be crucial in keeping our future climate in check.
The authors thankĀ Dr David EtheridgeĀ for his advice on the use of proxy measurements to infer carbon dioxide levels in past atmospheres.
Editorās Note
This article was first published on The Conversation and is republished here under a Creative Commons licence. The Conversation is a highly recommended free website where academic researchers from across the world write about their research for a large public.
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