IPCC Fifth Assessment Report (AR5)

9 October 2013


On 27th September the Inter-governmental Panel on Climate change (IPCC) Working Group 1 (WG1 – The Physical Science Basis) released its updated findings on the evidence of climate change. Its headline conclusions were:

“Warming of the climate system is unequivocal”


“Human influence on the climate system is clear.”

The IPCC is a United Nations scientific body with a remit to provide the world with a clear scientific view on the current state of knowledge on climate change and its potential impacts. It does not produce any of its own research but reviews and assesses the latest scientific, technical and socio-economic information available world-wide.

The fifth assessment is the latest in a series of reports giving an up to date understanding of climate change and is split into four parts:

  •          Working Group I – The Physical Science Basis
  •          Working Group II – Climate Change Impacts- Adaption and Variability
  •          Working Group III – Mitigation of Climate Change
  •          Synthesis Report (drawing on the above three working groups)

It is the first of these that has recently been released giving the most up to date scientific understanding of climate science available having drawn on the evidence of over 9,200 scientific publications.

Observational updates in this report show, with an increasing level of certainty since the last report (AR4), that the atmosphere and ocean have warmed, that amounts of snow and ice have diminished, that sea levels have risen and that the concentrations of greenhouse gases have increased.

As examples, in the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1,400 years, it is virtually certain the upper ocean warmed from 1970 to 2010 and atmospheric concentrations of some greenhouse gases (including carbon dioxide) have reached unprecedented levels in the last 800,000 years.

New future predictions have also been produced since AR4 and the models used to make these have been developed so there is now a very high confidence they can reproduce observed continental-scale surface temperature patterns and trends over many decades.

Under all the future scenarios the global mean temperature will continue to rise unless greenhouse gas emissions are abated. These temperature changes will not be uniform although, in most places, it is virtually certain that there will be more hot and fewer cold temperature extremes. There are also predicted to be many other climate effects from an increase in the contrast in precipitation between wet and dry regions and seasons to the rate of global sea level rise exceeding that for the period 1971-2010.

There has been much coverage in the media about the slowdown or hiatus in global warming since 1998.  The IPCC report’s authors conclude that 15 years is still not a long enough timescale to draw firm conclusions about the reasons for the pause.  Published research on this is still relatively sparse.

The Welsh Government’s Climate Change Strategy was published in October 2010 and sets out the Welsh Government’s key targets relating to climate change. In addition to achieving at least a 40% reduction in total greenhouse gas emissions in Wales by 2020, the Welsh Government aim to reduce greenhouse gas emissions by 3% per year from 2011 in areas of devolved competence (against a baseline of average emissions between 2006-10). December 2013 will be the first time the Welsh Government will be reporting on delivery of the 3% target.

Further Information

IPCC, Climate Change 2013: The Physical Science Basis, Headline Statements from the Summary for Policymakers

IPCC, Climate Change 2013: The Physical Science Basis, WGI Fact Sheet

IPCC, Climate Change 2013: The Physical Science Basis, Summary for Policy Makers

Article by Matthew McLeod

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