November 8, 2016

expert reaction to study of the growth rate of atmospheric CO2

A pause in the growth rate of carbon dioxide in the atmosphere is reported in the journal Nature Communications with the researchers also reporting a decline in the fraction of man-made emissions remaining in the atmosphere despite an increase in the levels of those emissions.

Prof. Chris Rapley, Professor of Climate Science at UCL, said:

“This study points out that over the last decade the atmospheric CO2 content and global temperature continued to rise, but the rate of temperature rise slackened; as a result, plants appear to have absorbed CO2 more readily. The authors make it clear that this effect is almost certainly temporary.

“What this research does not show is that humanity can relax when it comes to the dangers to agriculture posed by climate change. The ‘greening’ effect of CO2 will ultimately be overwhelmed by the plants’ own respiration and decay, which will cause even more CO2 to be released. The plants that are currently benefitting include woody inedible varieties and weeds; and while some useful plants (like wheat and rice) can benefit from elevated CO2 – as long as temperatures don’t go up too much! – many others (such as maize and sugar cane) do not benefit to anything like the same extent.

“The balance of evidence indicates that any beneficial effects of CO2 will be more than cancelled out by harmful ongoing temperature rises.”

Prof. Corinne Le Quéré, Director of the Tyndall Centre at the University of East Anglia, said:

“Natural vegetation is a fantastic help in slowing down climate change by absorbing about a quarter of our carbon emissions from burning fossil fuels. This so-called natural ‘carbon sink’ is extremely sensitive to climate though. The new study shows a bigger sink on land during 2002-2014. It seems this could be already reversing with the big El Niño of 2015-2016 triggering a smaller sink.

“This study highlights just how sensitive the natural environment is to a changing climate and how important it is to protect natural vegetation so it continues to absorb part of our carbon emissions. Fundamentally though, the carbon sinks help but their help is not enough to stop the planet to warm – far from that – carbon emissions have to drop to almost zero to stop global warming.”

Prof. Dave Reay, Chair in Carbon Management at the University of Edinburgh, said:

“This study makes clear just how important global carbon sinks are in determining our climate pathway through the 21st century. The land and oceans have been bailing us out of dangerous climate change for decades, but as temperatures rise and rainfall patterns change they will inevitably falter. Unless key carbon sinks such as forests are better protected, the delicate green veil that has saved our worst climate blushes will be in tatters.”

Prof. Meric Srokosz, Marine Physics and Ocean Climate Scientist at the National Oceanography Centre, University of Southampton, said:

“While the rate of accumulation of CO2 in the atmosphere may have slowed, it continues to rise at an alarming rate and with that rise the Earth will continue to warm. Extra absorption of CO2 by the terrestrial biosphere may offset anthropogenic emissions to some degree but that does not excuse us from seeking to cut those emissions by reducing our fossil fuel use.”

‘Recent pause in the growth rate of atmospheric CO2 due to enhanced terrestrial carbon uptake’ by Trevor Keenan et al. published in Nature Communications on Tuesday 8 November. 

Declared interests

None declared