A rise in sea levels is described by directors of this study as especially hard to predict. In the past year scientists have reported on ice activity, especially in the two-mile thick Greenland Ice Sheet, that is presenting much new data and dynamic shifts never seen before.
Overall, the study is expected to report that the world's scientists now agree that global warming will bring more loss of snow and ice cover and changes in weather patterns, drought and heavy precipitation.
It also is likely to confirm recent findings that some carbon dioxide emissions are being absorbed by the oceans and thus raising ocean water acidity - which interferes with the basic metabolism of many sea creatures.
Because so many scientists and governments all need to agree on an IPCC report, past versions have tended to be conservative in nature. Scientists say that, in retrospect, the first three assessment reports (1990, 1995, 2001) each understated what actually happened in the real world.
The IPCC was established in 1988 by the World Meteorological Organization and the United Nations Environment Program to assess the "risk of human-induced climate change."