Fossil fuel emissions would have to be cut by further 20 percent to meet 1.5 °C target

Global fossil fuel emissions would have to be reduced by as much as 20% more than previous estimates to achieve the Paris Agreement targets, because of natural greenhouse gas emissions from wetlands and permafrost, new research has found.

The additional reductions are equivalent to 5-6 years of carbon emissions from human activities at current rates, according to a new paper led by the UK's Centre for Ecology & Hydrology.

The 2015 Paris Climate Agreement aims to keep "the global average temperature increase to well below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels".

The research, published in the journal Nature Geoscience today (July 9, 2018) uses a novel form of climate model where a specified temperature target is used to calculate the compatible fossil fuel emissions.

The model simulations estimate the natural wetland and permafrost response to climate change, including their greenhouse gas emissions, and the implications for human fossil-fuel emissions.

Natural wetlands are very wet regions where the soils emit methane, which is also a greenhouse gas. The methane emissions are larger in warmer soils, so they will increase in a warmer climate.

Permafrost regions are those which are permanently frozen. Under a warming climate, permafrost regions begin to thaw and as a result the soils begin to emit carbon dioxide, and in some cases methane, into the atmosphere.

The greenhouse gas emissions from natural wetland and permafrost increase with global temperature increases, this in turn adds further to global warming creating a "positive feedback" loop.

The results show the "positive feedback" process are disproportionately more important for the emission reductions needed to achieve the 1.5 °C target rather than the 2 °C target.

This is because the scientists involved in the study modelled the impact of the additional processes for the time-period 2015-2100, which are broadly similar for the two temperature targets.

However, as the emissions budgets to achieve the 1.5 °C target are half of what is required to meet the 2 °C target, the proportional impact of natural wetlands and permafrost thaw is much larger.

Lead author Dr Edward Comyn-Platt, a biogeochemist at the UK Centre for Ecology & Hydrology said: "Greenhouse gas emissions from natural wetlands and permafrost regions are sensitive to climate change, primarily via changes in soil temperature.

"Changes in these emissions will alter the amount of greenhouse gases in the atmosphere and must be considered when estimating the human emissions compatible with the Paris Climate Agreement."

Co-author Dr Sarah Chadburn, of the University of Leeds, said: "We found that permafrost and methane emissions get more and more important as we consider lower global warming targets.

"These feedbacks could make it much harder to achieve the target, and our results reinforce the urgency in reducing fossil fuel burning."

Co-author Prof Chris Huntingford, of the Centre for Ecology & Hydrology, said: "We were surprised at how large these permafrost and wetland feedbacks can be for the low warming target of just 1.5°C."

The other institutions involved in the research were the University of Exeter, the Met Office Hadley Centre, Exeter, the University of Reading and the Joint Centre for Hydrometeorological Research, Wallingford.

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Contact details: For interview requests, please contact Simon Williams, Media Relations Officer, the Centre for Ecology & Hydrology, UK. email simwil@ceh.ac.uk. Tel: +44 (0)792 295384.

Lead author: Dr Edward Comyn-Platt, biogeochemist at the Centre for Ecology & Hydrology, UK. e-mail: edwcom@ceh.ac.uk. Tel: +44 (0)1491 692509.

Co-author: Dr Sarah Chadburn, research associate, University of Leeds, UK. e-mail: S.E.Chadburn@exeter.ac.uk

Paper reference: Comyn-Platt, E.; Hayman, G.; Huntingford, C.; Chadburn, S. E.; Burke, E. J.; Harper, A. B.; Collins, W. J.; Webber, C. P.; Powell, T.; Cox, P. M.; Gedney, N.; Sitch, S. (2018) Carbon budgets for 1.5 and 2C targets lowered by natural wetland and permafrost feedbacks. Nature Geoscience. The paper will be available online when the embargo ends at https:/ / doi. org/ 10. 1038/ s41561-018-0174-9

Funders: The work was undertaken by the CLIFFTOP, CLUES and MOC1.5 projects as part of the UK Natural Environment Research Council's programme "Understanding the Pathways to and Impacts of a 1.5°C Rise in Global Temperature". Those involved in the study also acknowledge the funding support from the Joint UK BEIS/Defra Met Office Hadley Centre Climate Programme, the EU-funded CRESCENDO project, the EPSRC Fellowship "Negative Emissions and the Food-Energy-Water Nexus" and the CEH National Capability Funding.

Institutional details:

The Centre for Ecology & Hydrology (CEH) is the UK's Centre of Excellence for integrated research in the land and freshwater ecosystems and their interaction with the atmosphere. CEH is part of the Natural Environment Research Council (NERC), employs more than 450 people at four major sites in England, Scotland and Wales, hosts more than150 PhD students and has an overall budget of about £35m. CEH tackles complex environmental challenges to deliver practicable solutions so that future generations can benefit from a rich and healthy environment. http://www. ceh. ac. uk Follow the latest developments in CEH research via Twitter at - @CEHScienceNews

University of Exeter

The University of Exeter is a Russell Group university that combines world-class research with very high levels of student satisfaction. Exeter has over 21,000 students and is in the top one per cent of universities worldwide. Exeter is also ranked 9th in The Times and The Sunday Times Good University Guide 2017 and 11th in the Guardian University Guide 2017. In the 2014 Research Excellence Framework (REF), the University ranked 16th nationally, with 98% of its research rated as being of international quality. Exeter was named The Times and The Sunday Times Sports University of the Year 2015-16, in recognition of excellence in performance, education and research. Exeter was The Sunday Times University of the Year 2012-13. http://www. exeter. ac. uk

Met Office

The Met Office is the UK's National Meteorological Service, providing 24x7 world-renowned scientific excellence in weather, climate and environmental forecasts and severe weather warnings for the protection of life and property. The Met Office Hadley Centre for Climate Science and Services provides world-class guidance on the science of climate change and is the primary focus in the UK for climate science. Its work is, in part, jointly funded by BEIS (Department for Business, Energy and Industrial Strategy) and DEFRA (Department for Environment, Food and Rural Affairs). http://www. metoffice. gov. uk

University of Leeds

The University of Leeds is one of the largest higher education institutions in the UK, with more than 31,000 students from 147 different countries, and a member of the Russell Group research-intensive universities. We are a top 10 university for research and impact power in the UK, according to the 2014 Research Excellence Framework, and positioned as one of the top 100 best universities in the world in the 2015 QS World University Rankings. We are The Times and The Sunday Times University of the Year 2017. http://www. leeds. ac. uk

University of Reading