Outline of the IPCC Fourth Assessment Report (AR4)

Abstract

This article outlines the latest scientific knowledge on global warming/climate change, especially in the meteorological and climatological fields, presented in the fourth assessment report (AR4) from Intergovernmental Panel on Climate Change (IPCC) in 2007, and provides a comparison with the third assessment report (TAR). In the review of WG1 report, we summarize “Observed recent climate change” and “Future climate projection, ” referring to major events and climate variables. In the review of WG2, we summarize the results on the main potential impacts of global warming projected on the natural environment and ecosystems in the future. Finally, a review of downscaling studies is presented, which are very important as they provide a bridge between regional scale climate change information presented in WG1 and WG2.
Since TAR, progress in understanding how climate is changing in space and in time has been gained through improvements and extensions of numerous datasets and data analyses, broader geographic coverage, better understanding of uncertainties, and a wider variety of measurements. Understanding of anthropogenic warming and cooling influences on climate has also improved. AR4 concludes with very high confidence (higher than TAR) that : i) climate warming is unequivocal and ii) the global average net effect of human activities since 1750 has been one of warming. In studies on the impacts of global warming, understanding of global warming risk is evaluated more quantitatively based on greatly increased studies of observed trends in the physical and biological environment and their relationships with regional climate change, as well as improved future climate projections on a regional scale.