What emission profiles aid remaining below two degrees of global warming?

In recent days multiple marches have taken place around the world, timed to coincide with the UN Climate Change summit in New York (23 September 2014). The many protestors have urged more action by governments to reduce greenhouse gas emissions.

CEH climate modeller Dr Chris Huntingford commented:

“There is still significant debate as to what constitutes safe levels of global warming. This almost certainly depends on the different impacts which can result from varying levels of warming. For example, meteorological changes affecting crop productivity detrimentally could be produced by a different level of climate change to that causing unwelcome sea-level rise. Yet despite this, the 2009 climate conference in Copenhagen pushed for the single threshold of no more than two degrees of global warming. There is a persuasive argument that this was a major achievement, as a single easy to understand temperature threshold will probably gain more traction in policymaker circles than debating a range of possible climatic futures.

The immediate question then became: “What emissions profiles can keep us below two degrees of global warming?” Working with colleagues from Met Office Hadley Centre, University of Oxford, Manchester Metropolitan University and the Committee on Climate Change, we carried out a study using a relatively simple coupled climate-carbon cycle model, but one capturing uncertainty based on differences between the fully complex climate models, as operated by various research centres across the world. The resultant paper provided “look-up” diagrams, where different emissions levels of years 2020 and 2050 can be related to the probability of remaining below two degrees. The paper also linked these 2020 and 2050 levels to both year of maximum emissions and required year-on-year emission cuts for the decades thereafter, in order to fulfil them.

The paper was published in 2012 in the journal Environmental Research Letters, but its message still stands. Namely that to have a reasonable chance of constraining warming to two degrees then emissions need to peak in the next few years, followed by year-on-year cuts of at least 3%.”

Chris Huntingford

UN Secretary General Ban Ki-Moon (front row, second from right) at the People's Climate
March in New York, held ahead of the Climate Summit he hosted at UN headquarters in
September 2014. Photo: UN / Mark Garten

Additional information

The paper can be read on the Environmental Research Letters website. It is "open access" allowing circulation of the document, and can be found here (doi: 10.1088/1748-9326/7/1/014039).

Chris Huntingford is a climate researcher at the UK Centre for Ecology & Hydrology, and also long-term visiting scientist at the Oxford University Centre for the Environment.

Information on the UN Climate Summit 2014