Freak weather a certainty, but IPCC report less sure on why

THE candid conclusion from the Intergovernmental Panel on Climate Change's summary report into managing extreme weather events is that scientific understanding of global weather systems leaves a lot of scope for further research.

The report concedes that extreme events are rare, making it difficult to say with precision what changes have taken place or what to expect in the future. On human impact, the report concludes that "anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures on the global scale".

And it says there is "medium confidence" that anthropogenic influences have contributed to intensification of extreme precipitation on the global scale.

The question of whether this has led to increased flooding is hotly contested. "There is low agreement in this evidence (regional flooding), and thus overall low confidence at the global scale regarding even the sign of these changes," the report says.

Given the central scientific thesis on climate change -- that increased atmospheric carbon dioxide will lead to rising global temperatures -- it would have been extraordinary had the report not forecast the prospect of more frequent heatwaves.

But what this actually means remains uncertain and will not become clear for decades.

The report dismisses the more exaggerated predictions of wholesale changes in the world's weather, saying; "There is low confidence in projections of changes in large-scale patterns of natural climate variability."

The bottom line is, even using a range of emissions scenarios, natural climate variability will dominate until mid-century.

"Even the sign of projected changes in some climate extremes over this timeframe is uncertain", it says.

Underscoring the poor level of scientific understanding, the report adds that "assigning 'low confidence' for projections of a specific extreme neither implies nor excludes the possibility of changes in this extreme".

The report says it is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes and decreases in cold extremes will occur on the global scale during this century.

It is likely that the frequency of heavy precipitation or the proportion of total rainfall from heavy falls will increase this century over many areas of the globe.

Average tropical cyclone maximum wind speed is likely to increase but not in all ocean basins. And it is likely that the global frequency of tropical cyclones willeither decrease or remain essentially unchanged over the next four decades.

The report says there is medium confidence that droughts will intensify in some seasons and areas, including southern Europe and the Mediterranean region, central Europe, central North America, Central America and Mexico, northeast Brazil, and southern Africa.

Elsewhere, however, there is overall low confidence because of inconsistent projections of drought changes.

And there is low confidence in observed trends in tornadoes and hail because of inadequacies in monitoring systems.

Not surprisingly, the report says there is high confidence that locations currently experiencing adverse impacts such as coastal erosion and inundation will continue to do so due to increasing sea levels, "all other contributing factors being equal".

The timing of the extreme weather report is significant because it deals directly with one of the central issues to be discussed at the IPCC's most important annual meetings, which starts in Durban in South Africa next Monday.

With negotiations for a binding international agreement to cut carbon emissions stalled, the IPCC is hoping to claim progress in the establishment of a multi-billion-dollar global fund to help the developing world cope with the impacts of climate change.

The findings of this report are not as pointed as some advocacy groups may have hoped. But the report does not lessen the case for better urban planning and infrastructure in the developing world.

The key finding is that rapid urbanisation and poor planning greatly increase the risk of costly damage from bad weather, whether it is caused by climate change or not.