This is in part because the research that goes into the reports can be years old before it's published. The reports are highly respected for their scientific rigour, but conservative because of the consensus driven approach that the process requires. The wording for the Summary for Policymakers is additionally vetted by governments around the world . . .
We've also heard repeated alerts from scientists about how these effects of climate change are accelerating faster than predicted and beyond the levels predicted by both AR4 and earlier scientific research/projection.
These alerts continue and while it's possible to tune them out, we should probably listen more carefully and act on them, given that the scientists themselves are becoming increasingly alarmed and vocal, to the point where they are starting to (in certain cases) break their 'code of professional restraint' and tell us how bad the situation really is. They urge to take urgent and significant action to reduce our emissions.
Note this story from the ABC
Professor Field says that a warming planet will dry out forests in tropical areas, making them much more likely to suffer from bushfires.
One of the world's leading experts on climate change says a Nobel Prize-winning panel of scientists seriously underestimated the reality of global warming when it published its report just over a year ago.
Professor Chris Field, a leading member of the Intergovernmental Panel on Climate Change (IPCC), which released the report, says he and his fellow researchers did not have access to vital data. Professor Field says that a warming planet will dry out forests in tropical areas, making them much more likely to suffer from bushfires.
He says recent climate studies suggest global warming could also melt permafrost in the Artic tundra. These events would release billions of tons of greenhouse gasses that could raise global temperatures even more.
The report did not have data on emissions of carbon dioxide between 2000 and 2007 which show far more rapid rises than had been predicted. These increases in carbon have been caused principally by the burning of coal for electric power in India and China.
He has told an American science conference in Chicago that global warming is likely to accelerate at a much faster pace and cause more environmental damage than previously predicted. "Fossil emissions have proceeded much more rapidly than anticipated in any of the scenerios that were characterised in detail," he said. "The consequence of that is that we are basically entering a domain of climate change that has not been explored by the models. "We're on a different trajectory of emissions and therefore an unknown trajectory of warming."