The Fifth Assessment: What Is It And What Does It Tell Us?

p074-077-ABS#33-Green-1By Mark O’Brien.

Recently, the media has been reporting that the latest report on the science of climate change has been released by the Intergovernmental Panel on Climate Change (IPCC). This report has stirred up plenty of commentary, especially while the fires in NSW were burning during October. A lot of the commentary is focussed on particular aspects of the report and how they interact with the politics of climate change in Australia.

This article avoids the politics that swirl around the topic of climate change; it is not my role to try to convince you of the pros and cons of “direct action”, “scrapping the carbon tax”, “emissions trading”, or where to set Australia’s emission targets into the future. This article details what the report is, who wrote it, what the conclusions are and what more can be expected from the IPCC.

What Is The Fifth Assessment Report?

First of all, who is the IPCC? Established by the World Meteorological Organization (WMO) and United Nations Environment Programme (UNEP), the IPCC is open to all Members of the UN and of the WMO. Its task is to assess information (scientific, technical and socio-economic) relevant to understanding climate change, its potential impacts and adaptation and mitigation options.

Every six years the IPCC releases a comprehensive assessment of the scientific knowledge on climate change, with the last being released in 2007. Its reports are “policy-relevant but are not policy-prescriptive”.

The Fifth Assessment Report (AR5) is placing greater emphasis on assessing climate change’s socio-economic aspects and sustainable development implications. It has several “cross-cutting themes”, including changes, impacts and responses of water and the earth system, carbon cycle including ocean acidification, and ice sheets and sea-level rise.

AR5’s four parts are to be released progressively between September 2013 and November 2014. Three Working Groups (I, II and III) are each preparing full reports and an associated Summary for Policymakers (SPM) on specific issues: physical science, impacts, adaptation and vulnerability, and mitigation. A Synthesis Report will also be produced which will draw upon the assessments made by the Working Groups.

The first part of AR5, prepared by Working Group I (WGI), has been finalised and assesses the physical science of the climate system. The final draft has over 2,000 pages of text and 1,250 scientific figures and graphs. The 14 chapters cover topics such as atmospheric greenhouse gases, the carbon cycle, clouds and aerosols, as well as changes in temperatures, rainfall, glaciers, oceans and sea level. It also assesses climate models and projections, plus the causes and attribution of climate change.

Who Writes These Reports?

For WGI’s report alone, 209 Lead Authors, 50 Review Editors and more than 600 Contributing Authors with expertise or specific knowledge in a given area across many different disciplines were utilised. In excess of 50 Australian researchers had direct input into the report, with several doing so at the Lead Author level. Author selection gives consideration to regional representation, gender balance and involving experts not involved in previous IPCC assessments.

The IPCC does not conduct its own research, with priority given to peer-reviewed literature if available. WGI’s author teams assessed thousands of sources of scientific and technical information during the report’s development, with over 9,200 publications cited. Expert reviewers and governments are invited at different stages in the report’s development to comment on the scientific and technical assessment, and the draft’s overall balance. There were nearly 55,000 comments from 1,089 expert reviewers and 38 governments.

What Does The Report Conclude?

The following points are some of the highlighted conclusions from the WGI’s SPM. All images and conclusions are taken from IPCC 2013 “Working Group I Contribution to the IPCC Fifth Assessment Report, Climate Change 2013: The Physical Science Basis, Summary for Policymakers”, IPCC, Geneva.

The climate system’s warming is unequivocal:

  • many of the observed changes since the 1950s are unprecedented over decades to millennia;
  • the atmosphere and ocean have warmed;
  • the amounts of snow and ice have diminished;
  • sea level has risen; and
  • the concentrations of greenhouse gases have increased.

Atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. CO2 concentrations have increased by 40 per cent since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions.

Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1,400 years (medium confidence).

Ocean warming accounts for more than 90 per cent of the energy accumulated between 1971 and 2010 (high confidence). It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971.

Over the last two decades:

  • the Greenland and Antarctic ice sheets have been losing mass;
  • glaciers have continued to shrink almost worldwide; and
  • Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence).

The rate of sea level rise since the mid-19th Century has been larger than the mean rate during the previous two millennia (high confidence). Over the period 1901–2010, global mean sea level rose by 0.19 [0.17 to 0.21] m.

The ocean has absorbed about 30 per cent of the emitted anthropogenic carbon dioxide, causing ocean acidification.

The WGI report concludes that human influence on the climate system is clear and extremely likely to have been the dominant cause of the observed warming since the mid-20th Century. It has been detected in:

  • warming of the atmosphere and ocean
  • changes in global water cycle
  • reductions in snow and ice
  • global mean sea level rise
  • changes in some climate extremes.

What Comes Next (Report-wise, Not Projections)?

Working Group II’s (WGII) report will be considered in Yokohama, Japan in March 2014. It is assessing socio-economic and natural systems’ vulnerability to climate change, negative and positive consequences, and options for adaptation.

The inter-relationship between vulnerability, adaptation and sustainable development is being taken into consideration. Information is assessed by sectors such as water resources; ecosystems; food and forests; coastal systems; industry; human health. It is also assessed for regions across the globe.


Working Group III’s (WGIII) task is to examine climate change mitigation with its report scheduled to be considered in Berlin, Germany in April 2014. WGIII’s report will assess options for mitigating climate change through preventing, limiting or removing emissions from the atmosphere. This report will analyse costs and benefits of different mitigation approaches, both from a near- and long-term perspective, as well as considering available instruments and policy measures.

Finally, by October 2014, all WG conclusions will have been pulled together into a Synthesis Report (SR) which will be considered in Copenhagen, Denmark. The SR will synthesise and integrate AR5 material and will be written in a non-technical style, suitable for policymakers, in particular from governments, their advisors and experts as well as others in the community. While largely self-contained, it will guide readers to the underlying material if they wish to look further.


Mark O’Brien has over 20 years environmental experience and has been working with business for over 15 years on all aspects of their carbon performance. His company, Beyond Neutral®, specialises in carbon footprints, emissions reporting including NGERS, carbon management and reduction strategies and supplies quality carbon offsets from exciting international projects helping some of the world’s poorest people. Mark was the 2009 Certified Environmental Practitioner of the Year for Australia and NZ, and he is a Fellow of the Environment Institute of Australia and NZ. For more information, please contact Mark at, 02 6249 7209 (T), or visit Beyond Neutral®’s website


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