Dr Whetton says evidence from global air and ocean temperatures, melting snow and ice, and rising sea level show that warming of the climate system is now unequivocal.
"We now have improved understanding of how the climate is changing, based on improved datasets and analyses with broader geographical coverage, a wider variety of measurements and better understanding of uncertainties," she says.
"It is very likely that most of the rise in global average temperatures since the mid-20th century has been caused by increased greenhouse gas concentrations in the atmosphere. In other words, there is a greater than 90 per cent chance that temperatures are rising due to human activities. Human influences are also evident in changes to some types of extreme weather."
The report states that atmospheric concentrations of the main greenhouse gases, carbon dioxide and methane far exceed concentrations over the previous 650,000 years, primarily due to combustion of fossil fuels, agriculture and land-use changes.
Depending on how humans emit greenhouse gases in future, Dr Whetton says the range of projected globally-averaged surface warming for the end of the 21st century is between 1.0 and 6.3 degrees Celsius. Warming over Australia will be similar to the global rate.
"We also have a better understanding of how precipitation patterns are likely to change," Dr Whetton says. "Increases in the amount of precipitation are very likely in high latitudes, while decreases are likely in most subtropical land regions, including southern Australia."
The IPCC Working Group 1 report, Climate Change 2007: The Physical Science Basis, assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change.
The IPCC represents the consensus view of about 2500 climate scientists from around the world. More than 100 Australian experts have been involved in the IPCC process since 2001.