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Why ‘400ppm’ is a number we should all care about


Over recent weeks, climate scientists and environmentalists have been carefully watching the output from a remote data collection point in Mauna Loa, Hawaii, which measures the volume of carbon dioxide (CO2) in the Earth’s atmosphere. And now we’ve heard confirmation that levels have reached 400 parts per million (400ppm) – the highest since the Pliocene era, which finished 3 million years ago. As recently as 1960, carbon dioxide levels were at around 320ppm.

Mauna Loa record, showing steady rise of carbon dioxide concentrations since 1960Mauna Loa record, showing steady rise of carbon dioxide concentrations since 1960. © Scripps Institution of Oceanography

Why does this matter? Scientific data suggests that sea levels during the Pliocene era were between 5 and 40 metres above those of today, and average global temperatures were 3 to 4 degrees higher.

Some impacts of the recent increase in carbon dioxide levels can be easily measured – for example, just this week scientists reported on the rapid acidification of surface waters in the Arctic, which is a result of increased absorption of carbon dioxide. Oceans worldwide are now 30% more acidic than at the start of the Industrial Revolution.

Following a period of over a decade during which summer sea ice in the Arctic declined consistently, it reached a new low in 2012, at 49% below the 1979–2000 average minimum. Global sea levels averaged over the past decade were about 20 cm (8 inches) higher than pre-industrial levels.

Others impacts of climate change – how it effects our weather for example – can be more challenging to measure. While it’s not possible to attribute any one extreme weather event to climate change, science suggests that the changes to our climate are increasing the probability and severity of extreme weather events such as Hurricane Sandy.

So what is being done about this worrying trend? Well, not enough. Ultimately it’s governments that need to take a lead.

Last week, delegations from around the world converged in Bonn in Germany to discuss the future of the United Nations climate change process, and the mechanisms for reaching a global deal. The irony of coal barges sailing along the Rhine past the conference centre, while progress inside was slow, was not lost on many delegates.

With the exception of small island states like the Maldives – whose very existence is threatened by sea level rise – it’s easy for most politicians to push climate change to the bottom of their list of priorities, faced with the day-to-day challenges of governing. But this is one problem that is not going away, and tackling it will require both courage and strong leadership from our governments.

A recent report from the internationally respected Grantham Institute on climate change and carbon tracker organisations showed that keeping global climate change within 2° means leaving 60-80% of the world’s known fossil fuel reserves in the ground.

Governments need to wake up to this problem and agree to collective action sooner rather than later.

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