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A significant marker of rising global greenhouse gas emissions has been passed, with a key monitoring site on Tasmania’s north-west tip recording atmospheric carbon-dioxide exceeding 400 parts per million for the first time.

As foreshadowed by Fairfax Media last week, a baseline reading at the Cape Grim station that exceeded the 400-ppm mark of the primary gas driving global warming was imminent.

As it turned out, “the unfortunate milestone” was reached on Tuesday May 10 at 8am, local time, said Peter Krummel, who heads the CSIRO team analysing data from the most important site in the southern hemisphere.

Atmospheric readings from Cape Grim, along with two stations in Hawaii and Alaska, are closely watched as they date back decades and closely track a range of pollutants from ozone-depleting chemicals to the various greenhouse gases resulting from burning fossil fuels and clearing forests.

Mr Krummel said that while mostly symbolic, the 400-ppm reading “highlights the problem of rising emissions, which are increasing more rapidly than they used to be”.

A report out earlier this year from the World Meteorological Organization noted atmospheric readings of CO2 at the Mauna Loa site in Hawaii rose 3.05 ppm in 2015 alone – the biggest increase in the 56 years of research……

Climate scientists, such as David Karoly at Melbourne University, note that when other greenhouse gases, such as methane, are included, the situation is even bleaker.

The so-called carbon dioxide-equivalent level that takes in the full global warming impact is now about 485 ppm.

Both 2014 and 2015 were record hot years globally in data going back about 130 years. With the effect of a strong El Nino overlaying long-term trends, this year is likely to be even hotter after a scorching start.

http://www.theage.com.au/environment/climate-change/confirmed-southern-hemisphere-co2-level-rises-above-symbolic-400-ppm-milestone-20160515-govfq7.html#ixzz48llBSOAT