Scientific evidence of climate change – According to the Intergovernmental Panel on Climate Change (IPCC), the leading international body for assessing the science related to climate change, warming of the climate system is unequivocal. This is seen in many independent lines of evidence: the warming of the atmosphere and ocean, reductions in snow and ice, and rising sea level.
The IPCC is currently finalizing its Fifth Assessment Report (AR5). The Working Group I contribution to AR5, dealing with the physical basis of climate change, was released at the end of September 2013.
The assessment shows that increasing concentrations of carbon dioxide and other greenhouse gases have led to an uptake of energy in the climate system.
Among its key findings, IPCC Working Group I concludes:
- - Warming of the climate system is unequivocal;
- - Human influence on the climate system is clear;
- - Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.
The IPCC assessment finds that each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.
The year 2013 is on course to be among the top ten warmest years since modern records began in 1850, according to the World Meteorological Organization (WMO) in its Provisional Statement on Status of Climate in 2013 released in November 2013.
The WMO’s latest Greenhouse Gas Bulletin published in November 2013 shows that the amount of greenhouse gases in the atmosphere reached a record high in 2012.
Far-reaching impacts – The impact of climate change on extreme weather events such as heat waves, floods, droughts and tropical cyclones, and possible responses to them, is examined in the IPCC’s Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX).
Further information on how climate change is impacting human and natural systems, future risks, and options for adaptation, will be available when IPCC Working Group II, which deals with impacts, adaptation and vulnerability, publishes is contribution to AR5 at the end of March 2014.
Adaptation – acknowledging climate change and putting systems in place to increase our resilience – is one possible response to climate change.
Tackling the causes of climate change – Another possible response is mitigation – cutting down on the greenhouse gas emissions that are influencing climate change.
One way of doing this is using renewable energy as an alternative to fossil fuels, something examined by the IPCC in its Special Report on Renewable Energy Sources and Climate Change Mitigation (SRREN).
IPCC Working Group III, which deals with the mitigation of climate change, will provide further information on options for mitigation, when it releases its contribution to AR5 in April 2014. It will examine the impact on emissions of different sectors such as energy, transport, construction, industry and agriculture, and examine possible future pathways for emissions and how they may affect temperatures.
Science and policy – The findings of the three IPCC contributions will be brought together in the AR5 Synthesis Report to be finalized in October 2014. The Synthesis Report will be written in a non-technical style suitable for policymakers.
Assessments such as the IPCC’s AR5 and other scientific reports are used by governments to formulate policy and by other decision-makers, and also feed into negotiations such as the United Nations climate change conference.
Because of the impact of climate change set out by the IPCC, governments have agreed to limit the rise in temperatures to 2ºC from pre-industrial levels.
The latest Emissions Gap Report, produced by the United Nations Environment Programme (UNEP) in November 2013, examines the prospects of meeting this target. It finds that the chance of remaining on the least-cost path to keeping the global temperature rise to below 2ºC will swiftly diminish and open the door to a host of challenges if the global community does not immediately embark on wide-ranging actions to narrow the greenhouse gas emissions gap in 2020 – the difference between the pledges that countries have made to cut warming gases and the targets required to keep warming below 2ºC.
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