IPCC: Climate impact risk set to increase

There has been uncertainty over the link between extreme weather events and climate change

The risk from extreme weather events is likely to increase if the world continues to warm, say scientists.

A report by the Intergovernmental Panel on Climate Change said it was "very likely" that emissions had led to an increase in daily maximum temperatures.

It added that emissions had also led some regions experiencing longer and more intense droughts.

The findings of the Special Report were presented at the IPCC's 34th Session, which is being held in Kampala, Uganda.

The details were outlined during a media briefing by the co-chairmen overseeing the compilation of two of the three segments of next IPCC assessment report.

Introducing the Summary for Policymakers of the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, IPCC chairman Rajendra Pachauri said: "It underlines the complexity and diversity of factors that are shaping human vulnerability to extremes."

The summary stated: "Extreme events are rare, which means there are few data available to make assessments regarding changes in their frequency or intensity."

However, it added: "There have been statistically significant trends in the number of heavy precipitation events in some regions."

On the possible change to hurricane patterns, it said: "Average tropical cyclone maximum wind speed is likely to increase, although increases may not occur in all ocean basins.

Storm clouds gathered over the IPCC after a number of errors were found in its 2007 assessment report

"It is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged."

The report also said that small island - as well as mountainous and coastal - settlements were likely to be particularly vulnerable as a result of sea-level rise and higher temperatures, in both developed and developing nations.

"Rapid urbanisation and the growth of mega-cities, especially in developing nations, have led to the emergence of highly vulnerable urban communities," it added.

A step too far?

Citing climate change as a factor that is contributing to more extreme weather events has long been a field of scientific research shrouded in controversy.

For example, a study published in 2009 showed that hurricanes in the North Atlantic were more frequent than in the previous 1,000 years, and while the authors said the current level of activity was unusual, they stopped short of suggesting there was a direct link with a warming world.

And earlier this year, another report said it had identified a link between an increase in greenhouse gas emissions and extreme rainfall events in the Northern Hemisphere.

While others had suggested that the global climate system - which shapes the planet's weather patterns - was too complex to make such assertions.

Prof Mike Hulme, professor of climate change at the University of East Anglia, UK, said that a warming world would create a greater risk of extreme weather, but it would be difficult to pinpoint what events were the result of greenhouse gas emissions.

"It becomes very difficult to isolate a single event, like a heatwave or a heavy rainstorm, and say that event was caused by the human element of climate change.

"In order to do that, you have to be able to tease apart the human aspect [from] the natural element.

"In my view, we do not have the tools or the knowledge to do that forensic teasing apart."

Chris Field, one of the co-chairmen of the working groups that oversaw the compilation of the report, said the IPCC decided to assess the science on the risks associated with extreme weather events because governments had requested more information.

"The IPCC looks at issues because they are important, not because we are looking for or looking to avoid controversy," he told BBC News.

Prof Field said that impacts of climate extremes had a cumulative effect, which had not been properly assessed.

"We have done a lot of analysis on what happens if the average temperature goes up by 2C, 4C or whatever," he explained.

"In general, there are mechanisms you can use to adjust to changes in average temperature, but it is much more difficult to be prepared for changes in the extremes.

"There are many features that make the extreme (weather events) difficult. They are difficult to predict - you don't know what kind of extreme is coming.

"They are also difficult to quantify, because you can have extremes that pile up on each other - multiple extremes, and extremes that occur in the context of other stresses."

Credibility control

Since the IPCC, the leading international body for the scientific assessment of climate change was established by the UN Environment Programme and the World Meteorological Organization (WMO) in 1988; it's main task has been to produce regular Assessment Reports.

To date, four have been published. Each one is deemed to be the most comprehensive analysis of climate change at the time of publication and is used as a tool in the formulation of climate change policy by national governments and international bodies.

The first report was published in 1990, and the next report (Assessment Report 5, also known as AR5) is scheduled to be completed in 2013/14.

The contents of most recent report, AR4, published in 2007, came under close scrutiny in 2010 after it came to light that the 3,000-page publication contained a number of errors, including the melt rate of glaciers in the Himalayas.

This led to questions being raised about the overall credibility of the report's findings, prompting UN Secretary-General Ban Ki-moon to ask the InterAcademy Council to convene a panel of experts to conduct an independent review.

Reporting back in August 2010, the umbrella body for the world's scientific bodies backed the main findings of the IPCC report, but called on it to put in place stricter checks to prevent damage to the organisation's credibility.

As well as discussing progress on the next assessment report, one of the issues to be negotiated by delegates at the gathering in Kampala, which runs until Saturday, is how to improve the processes and procedures in the formulation of AR5.

Prof Field said that he felt the IPCC's quality control had always been good, and the close scrutiny had only served to improve that further.

"We have learned some things over the past few years, and we are even more careful now," he said.

"I think that the quality control procedures that we used in this report were very carefully constructed and very carefully executed - I feel very good about the overall level of quality and scrutiny."

The next assessment report is set to be published in late 2013/2014.

The first segment, carried out by Working Group I, assesses "the physical science basis" of climate change is scheduled to be released mid-September 2013.

Working Group II's Impacts, Adaptation and Vulnerability report is expected to be publicly available by mid-March 2014, while Working Group III's findings on the "mitigation of climate change" will be published in early April 2014.

The final overall AR5 Synthesis report is expected to be released in October 2014.