Opinion: The 1.5 °C Challenge

Posted on Posted in Climate Science, Opinion

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A recent article in the Guardian newspaper highlights the implications of the Paris agreement to limit global warming to 1.5 °C compared to 2 °C as had been the generally accepted target prior to Paris – the implications bear directly on how we plan climate adaptation and mitigation policy for the Canadian prairies.

 

The Guardian article notes that there’s relatively little research that has looked specifically at the 1.5 °C warming scenario – but there is some and that which does exist shows a big advantage in achieving the Paris target. Last year a study by Erich Fischer of the Institute for Atmospheric and Climate Science in Zurich found that the risk of very hot days increases significantly in the gap between 1.5 and 2 °C. The likelihood of experiencing what was a “once in a 1,000 days” hot day has already increased fivefold. According to Fischer the likelihood of such extremely hot weather doubles again at 1.5 °C and doubles again if we go to 2 °C.  It’s a similar story for droughts; the extra half a degree from 1.5 to 2 °C increases the expected length of drought periods dramatically and marks the difference between a climate at the upper end of present-day variability and a fundamentally different, much more hostile climate. The Prairie Climate Atlas tells the story well – Winnipeg, which currently experiences about 12 hot days a year (above 30 °C), by the latter decades of this century that number could rise to over 40 days a year at which point we’d have a climate resembling present-day North Texas.

 

The environmental and political logic of the Paris target is obvious – it’s the technical challenge of limiting global warming to 1.5 °C that makes the story even more interesting. As of several weeks ago, the last hold-out climate station in the world (in Antarctica) reported an atmospheric CO2 concentration above 400 parts per million (ppm). Every station in the world is now reporting more than 400 ppm. The current crop of global circulation models generally agree that limiting warming to 1.5 °C requires that atmospheric CO2 rise no further than 430 ppm, which means 300 billion tonnes of CO2 can be added to the atmosphere. However even a very aggressive mitigation strategy that drops global CO2 emissions to zero by 2050 and stays at zero for the rest of the century produces 800 billion tonnes of additional CO2. So how do we resolve this rather fundamental 500 billion tonne gap to achieve 1.5 degrees?

 

According to Joeri Rogelj and his colleagues at the International Institute for Applied Systems Analysis in Austria, the answer is simple and inescapable – we use carbon dioxide removal (CDR) technology. CDR has existed on the fringes of climate science and policy for decades and has been considered – like (until recently) climate adaptation – a distraction to the priority task of cutting CO2 emissions. That may have been true in 1980 or even 1990, but Rogelj’s modelling shows that we’ve waited too long, and without CDR no plausible pathway exists to limit warming to 1.5 °C by 2100. What were rather outlandish ideas now have to be on the table – the math doesn’t pencil out any other way. So what is CDR? Like the name implies, it’s technology that removes CO2 from the atmosphere and ideally locks it up permanently to avoid re-release. At its simplest it can be afforestation (planting trees) and managing agricultural soils to sequester more carbon in its organic matter. More complex approaches use energy – which must come from a zero-carbon source – to chemically strip CO2 molecules from ambient air to produce a pure CO2 stream for use in industrial applications or geological sequestration. A CDR technology with a technical ambition commensurate with the political ambition expressed in Paris is bioenergy plus carbon capture and sequestration (BECCS). BECCS essentially reverses the fossil carbon to atmospheric carbon cycle that has characterized the fossil fuel era. With BECCS, forests for example continuously hoover up carbon from the atmosphere, store the carbon in tree biomass, which is then converted into energy at a power plant with the smokestack CO2 emissions captured and re-buried in bedrock.

 

So what are the stakes for the Prairies?  We know that climate change impacts are amplified on the Prairies, and we’ll likely reap disproportionate benefit by limiting global warming to 1.5 degrees.   Moreover the CDR technologies required to achieve 1.5 °C have one thing in common – they need productive geography – lots of it to work, whether for afforestation, soil carbon sequestration, the renewable energy to power CDR or the biomass systems for BECSS. And a lot of productive geography is one attribute the Canadian Prairies have in spades. Let’s keep it that way.

 

Further reading:

https://www.theguardian.com/environment/2016/jun/16/what-would-a-global-warming-increase-of-15c-be-like

http://www.nature.com/nclimate/journal/v5/n6/full/nclimate2617.html

http://www.nature.com/nclimate/journal/v5/n6/full/nclimate2572.html

 

Henry David (Hank) Venema, PhD

Director of Planning, Prairie Climate Centre  

International Institute for Sustainable Development
http://www.iisd.org