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The geographical distribution of fossil fuels unused when limiting global warming to 2 °C

2015; Nature Portfolio; Volume: 517; Issue: 7533 Linguagem: Inglês

10.1038/nature14016

1476-4687

Christophe McGlade, Paul Ekins,

CO2 Sequestration and Geologic Interactions

To limit global warming to a rise of 2 °C compared to pre-industrial levels, we cannot use all of our fossil fuel reserves; here an integrated assessment model shows that this temperature limit implies that we must leave unused a third of our oil reserves, half of our gas reserves and over 80 per cent of our coal reserves during the next 40 years, and indicates where these are geographically located. If global warming is to be limited in this century to the much-publicized 2 °C rise compared to pre-industrial levels, fossil fuel use and the associated release of greenhouse gases will need to be severely limited. This raises questions regarding the specific quantities and locations of oil, gas and coal that can be safely exploited. Christophe McGlade and Paul Ekins use an integrated assessment model to explore the implications of the 2 °C warming limit for different regions' fossil fuel production. They find that, globally, a third of oil reserves, half of gas reserves and over 80% of current coal reserves should remain unused during the next 40 years in order to meet the 2 °C target and that the development of resources in the Arctic and any increase in unconventional oil production are incompatible with efforts to limit climate change. Policy makers have generally agreed that the average global temperature rise caused by greenhouse gas emissions should not exceed 2 °C above the average global temperature of pre-industrial times1. It has been estimated that to have at least a 50 per cent chance of keeping warming below 2 °C throughout the twenty-first century, the cumulative carbon emissions between 2011 and 2050 need to be limited to around 1,100 gigatonnes of carbon dioxide (Gt CO2)2,3. However, the greenhouse gas emissions contained in present estimates of global fossil fuel reserves are around three times higher than this2,4, and so the unabated use of all current fossil fuel reserves is incompatible with a warming limit of 2 °C. Here we use a single integrated assessment model that contains estimates of the quantities, locations and nature of the world’s oil, gas and coal reserves and resources, and which is shown to be consistent with a wide variety of modelling approaches with different assumptions5, to explore the implications of this emissions limit for fossil fuel production in different regions. Our results suggest that, globally, a third of oil reserves, half of gas reserves and over 80 per cent of current coal reserves should remain unused from 2010 to 2050 in order to meet the target of 2 °C. We show that development of resources in the Arctic and any increase in unconventional oil production are incommensurate with efforts to limit average global warming to 2 °C. Our results show that policy makers’ instincts to exploit rapidly and completely their territorial fossil fuels are, in aggregate, inconsistent with their commitments to this temperature limit. Implementation of this policy commitment would also render unnecessary continued substantial expenditure on fossil fuel exploration, because any new discoveries could not lead to increased aggregate production.