“Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes 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.”

Thus begins the Headline Statements from the Summary for Policymakers released on September 27, 2013 by the Intergovernmental Panel on Climate Change (IPCC).

Since 1990, the IPCC has produced five Assessment Reports summarizing the state of knowledge on climate change. The reports look at current indicators of climate change and make predictions modeling different climate scenarios based on greenhouse gas (GHG) concentration trajectories. The scenarios describe the possible climate futures that are possible depending on how much GHG will be emitted in the future.

The latest report, Climate Change 2013 – The Physical Science Basis represents the contribution of IPCC Working Group I to the Fifth Assessment Report (September 2013). The final version of this report will be published in January 2014. The contributions of Working Groups II and III to the Fifth Assessment Report will be published during 2014.

Key Findings

Key report findings are summarized in the Headline Statements from the Summary for Policymakers and include the following:

Observations of the Climate System

• Based on direct measurements and remote sensing, 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.
• Ocean warming dominates the increase in energy stored in the climate system.
• Greenland and Antarctic ice sheets, glaciers, and sea ice have been losing mass and decreasing in extent. Sea levels have been rising.
• Since 1951, global average surface temperature has warmed by about 0.6 ⁰C (mean).
• Warming in the climate system is unequivocal.

Predictions

• Global surface temperature change for the end of the 21^st century is likely to exceed 1.5 ⁰C relative to 1850 for all scenarios.
• Global mean sea and ocean levels will continue to rise during the 21^st century (a much more rapid rise predicted now). Heat will penetrate to the deep ocean and affect ocean circulation.
• Sea ice, spring snow cover, and glaciers will reduce in size.
• Climate change will affect the carbon cycle process, which will exacerbate the increase in CO₂.
• Continued emission of GHGs will cause further warming and changes in all components of the climate system.

Drivers of Climate Change

• It is extremely likely that more than 50% of the warming since 1951 is due to the increase in GHGs and other anthropogenic factors.
• Human influence on the climate system is clear. This is evident from the increasing GHG concentration and observed warming.
• It is extremely likely that human influence has been the dominant cause of observed warming since the mid-20^th century.

Options

• Limiting climate change will require substantial and sustained reductions of GHG emissions.

Media Response

Release of the report generated extensive media coverage. In the United Kingdom, media coverage peaked the day after the report was released. The UK newspaper headlines revealed each paper’s editorial line with respect to climate change and often showed corresponding levels of scepticism about the trends, attributes, or impacts of climate change. However, for the most part, the message that humans are causing extra warming was reported without being questioned.

The Future

Despite the uncertainty and scepticism associated with climate change, the IPCC’s assertion that climate change is virtually unequivocal combined with growing acceptance that human activity is at least partially responsible for observed changes in climate metrics should inspire further dialogue and action. As stakeholders, NGOs, governments, and companies become increasingly aware of these pressures, they will be increasingly expected to take steps to reduce CO₂ emissions and demonstrate publically the ways in which they are achieving this.

About the IPCC

The IPCC is an international body devoted to the assessment of climate change. It seeks to provide the world with a clear scientific view of the current state of knowledge on climate change and to predict the potential environmental and socio-economic impacts of climate change. The IPCC reviews and assesses the most recent scientific, technical, and social-economic information produced worldwide that is relevant to understanding climate change.

Currently 195 countries are members of the IPCC. Governments of these countries participate in the review process, where the IPCC reports are accepted, adopted, and approved. The work of the IPCC seeks to be policy relevant, but policy-neutral. Thousands of scientists contribute to the IPCC’s work on a voluntary basis.

About the Author

Rachel Melbourne is an ecologist in the Bristol, U.K. office of Environmental Resources Management (ERM). She has extensive experience conducting habitat and protected species surveys and is a full member of the Chartered Institute of Ecology and Environmental Management (CIEEM).

Resources

Additional information on this topic is available at the following links:

• UK Government’s Response to Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5): The Latest Assessment of Climate Science.

• Analysis of media coverage from The Carbon Brief

• Working Group I Contribution to the IPCC Fifth Assessment Report… Summary for Policy Makers

Photograph: Tango Dancers by Dtimoske, United States.

Return to the EHS Journal Home Page