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Global warming likely to exceed 1.5°C but could be reduced in long term August

Posted on 2 Aug 2010 in

Global average temperature is likely to rise by more than 1.5°C above the pre-industrial level, but could be reduced in the long term through strong cuts in emissions of greenhouse gases, according to a new report jointly published today by the Grantham Research Institute on Climate Change and the Environment, the Centre for Climate Change Economics and Policy, and the Met Office Hadley Centre

The report on ‘Mitigating climate change through reductions in greenhouse gas emissions: is it possible to limit global warming to no more than 1.5°C?’, is being published to inform negotiations at the United Nations climate change conference, which is taking place in Bonn, Germany, between 2 and 6 August 2010. Countries are currently discussing what temperature goal should be set as part of an international treaty to tackle climate change.

The report draws on analyses from models at the Met Office Hadley Centre which project how global average temperature would change for different paths of global annual emissions of greenhouse gases, while taking into account many of the significant uncertainties.

Global average temperature has already risen by about 0.8°C since the end of the 19th century. The report concludes: “Even if global emissions fall from 47 billion tonnes of carbon-dioxide-equivalent in 2010 to 40 billion tonnes in 2020, and are then reduced to zero immediately afterwards, we estimate that there would be a maximum probability of less than 50 per cent of avoiding global warming of more than 1.5°C above the pre-industrial level”.

However, global average temperature could be reduced in the long term if global annual emissions are reduced strongly. The report states: “We have identified a number of emissions paths that offer a probability of 50 per cent of global average temperature being no more than 1.5°C above its pre-industrial level in the long term, but they involve temporarily overshooting the temperature goal for up to 100 years”.

However, the report warns: “It is very important to recognise that overshooting any temperature goal would generate risks of triggering feedback accelerations, such as the enhanced release of carbon from the thawing of soils that are currently frozen, or causing large-scale and potentially dangerous impacts that could be difficult to reverse, such as a loss of species, inundation of some land areas, or extensive bleaching of corals. More research is needed into the likelihood of triggering feedbacks or irreversible impacts, such as large rises in sea level, during temporary overshooting of a 1.5°C goal.”

The report points out: “Given the current uncertainties, one approach for policy-makers may be to take actions that will allow the option of switching at some later point to an emissions path that is consistent with a 1.5°C goal. Our analysis suggests that the range of global annual emissions of 40 to 48 billion tonnes of carbon-dioxide-equivalent in 2020, which would be consistent with a 2°C goal, might also be compatible with a 1.5°C goal, if it is assumed that emissions reductions could be quickly accelerated after 2020. Our findings suggest that aiming for the bottom end of this range for 2020 (i.e. taking strong action now) would reduce the risk of closing down the option of switching to a 1.5°C goal.”

However, it identified “four key characteristics of emissions paths that offer at least 50 per cent probability of global average temperature being no more than 1.5°C above its pre-industrial level in the long term, with a temporary overshoot of no more than 100 years”. These characteristics are:

  • they involve early and strong reductions in global annual emissions;
  • they require rapid reductions in annual global emissions after 2020;
  • they require low annual global emissions by 2100, with a floor close to zero emissions in the long term; and
  • they are based on the assumption that it is possible for the global average temperature to exceed the goal and then return over the course of several decades to no more than 1.5°C above the pre-industrial level.

The report concludes: “Overall, our results do not rule out the achievement of a 1.5°C goal in the long term. Our findings suggest that, given historical trends in global annual emissions of greenhouse gases and, even with early and strong action to reduce emissions, the likelihood of avoiding global warming of more than 1.5°C above the pre-industrial level is low. However, it may be possible to limit the rise to no more than 1.5°C above the pre-industrial level in the long term, if the global average temperature is allowed to overshoot the goal and fall over a period of several decades.”

Notes for Editors

  1. The Grantham Research Institute on Climate Change and the Environment was established in 2008 at the London School of Economics and Political Science(LSE). The Institute brings together international expertise on economics, as well as finance, geography, the environment, international development and political economy, to establish a world-leading centre for policy relevant research, teaching and training in climate change and the environment. It is funded by The Grantham Foundation for the Protection of the Environment, which also funds the Grantham Institute for Climate Change at Imperial College London.
  2. The Centre for Climate Change Economics and Policy was established in 2008 to advance public and private action on climate change through rigorous, innovative research. The Centre is hosted jointly by the University of Leeds and the London School of Economics and Political Science. It is funded by the UK Economic and Social Research Council and Munich Re.
  3. The Met Office is a Government Trading Fund agency owned by the Ministry of Defence (MOD). It is the UK’s Public Weather Service, providing the essential meteorological information that is used in public weather forecasts.

The Met Office operates as a National Severe Weather Warning Service (NSWWS) and as one of only two designated World Area Forecast Centres , providing worldwide weather forecast advice to the aviation industry. The Met Office employs more than 1,800 staff in offices around the world.

The Met Office has vast experience in world-class climate research, which it has carried out for more than a quarter of a century. The Met Office Hadley Centre, set up in 1990, is the UK’s official centre for climate research, and is acknowledged internationally as world leading. The scientific research carried out is under a directed policy focused programme. This programme is designed to provide the scientific basis that is required to help UK government policy-makers and other stakeholders in the UK and internationally (including commercial customers and the public) deal with climate change in the future and make better informed decisions.