The purpose of this report is to synthesize the most policy-relevant climate science published since the close-off of material for the last IPCC report. The rationale is two-fold. First, this report serves as an interim evaluation of the evolving science midway through an IPCC cycle - IPCC AR5 is not due for completion until 2013. Second, and most important, the report serves as a handbook of science updates that supplements the IPCC AR4 in time for Copenhagen in December 2009, and any national or international climate change policy negotiations that follow.
This report covers the range of topics evaluated by Working Group I of the IPCC, namely the Physical Science Basis. This includes: (i) an analysis of greenhouse gas emissions and their atmospheric concentrations, as well as the global carbon cycle; (ii) coverage of the atmosphere, the land-surface, the oceans, and all of the major components of the cryosphere (land-ice, glaciers, ice shelves, sea-ice and permafrost); (iii) paleoclimate, extreme events, sea level, future projections, abrupt change and tipping points; and (iv) separate boxes devoted to explaining some of the common misconceptions surrounding climate change science.
The report has been purposefully written with a target readership of policy-makers, stakeholders, the media and the broader public. Each section begins with a set of key points that summarises the main findings. The science contained in the report is based on the most credible and significant peer-reviewed literature available at the time of publication. The authors primarily comprise previous IPCC lead authors familiar with the rigor and completeness required for a scientific assessment of this nature.