Image caption Thomas Stocker argued local climate models have not been user-friendly

Providing information that policymakers can use is key to the Intergovernmental Panel on Climate Change (IPCC) as work begins on its next global assessment.

The report, known as AR5, will focus on factors that materially affect people's lives, such as the Asian monsoon.

It will also look at what aspects of climate change might be irreversible.

Leaders of the IPCC's scientific assessment were speaking to BBC News during a conference in South Korea aimed at modernising the organisation.

They indicated that procedures used in compiling AR5 will reflect some criticisms made in the wake of errors uncovered in its previous assessment, in 2007.

The recent review of the IPCC's procedures, conducted by the InterAcademy Council (IAC), an umbrella body for the world's science academies, said that some assertions about the likelihood of severe impacts were based on little research.

"Authors reported high confidence in statements for which there is little evidence, such as the widely-quoted statement that agricultural yields in Africa might decline by up to 50 percent by 2020," it noted.

The IAC recommended that the next assessment must deal much more carefully and consistently with uncertainties - and Chris Field, co-chair of the IPCC working group on impacts, adaptation and vulnerability, indicated the message had been taken on board.

"The fact of the matter is that climate change impacts are very poorly known," he told BBC News.

"We only have mature scientific studies for a small number of topics and a small number of places, so we need to recognise that and figure out how, in an environment where the information is limited, we can still provide valuable information.

"What I expect us to do is to use the uncertainty guidance very carefully so we can avoid problems where we seem to be asserting more confidence than the data will allow; but also provide value to a discussion where the confidence isn't necessarily very high.

"After all, most people spend their lives making decisions under uncertainty, and that's what dealing effectively with climate change demands - the same kind of decisions you make when you decide to buckle your seatbelt, or buy insurance for your house or invest in the financial markets."

Natural changes

Increasingly, computer models of climate change are projecting impacts on a region-by-region basis, rather than globally.

This is widely acknowledged as vital for policymaking. But previous IPCC reports have not necessarily produced regional assessments in the most user-friendly or relevant way, suggested Thomas Stocker from the University of Bern in Switzerland, co-chair of the climate science working group for AR5.

"We will start from the processes that are necessary to characterise regional climate change, such as the El Nino Southern Oscillation, the North Atlantic Oscillation, monsoon systems around the world," he said.

"The new approach is that we first assess our physical understanding of these fundamental processes: what are the elements that change them, how do they respond to a background change in albedo or temperature or shift in rain bands ?

"Once we've assessed that, we then ask how does this knowledge inform us for projecting the monsoon in India, for example, or Southeast Asia? What does it tell about El Nino projections? And so forth."

The belief is that this process will make it easier for governments - and people - to assess how their lives may be affected by climate change, and so make better-informed policy choices.

Another issue that AR5 will grapple with in much more detail than previously is the influence of natural cycles on climate, particularly in the near-term.

It's been really difficult to figure out what's the climate part vs the societal part Chris Field, IPCC working group co-chair

Within the last few years, the world has seen the cooling influence of La Nina restrain the rise in global temperatures, before a switch to El Nino conditions put 2010 on course to be one of the warmest few years - perhaps the warmest of all - in recent times.

Researchers attempting to project temperatures for the next decade or so have to factor in numerous natural cycles as well as greenhouse warming, and Dr Stocker admitted that it is a confusing picture.

"It is an emerging field, the uncertainties are large. You can find studies with a cooling over the next 10 years, and others showing an enhanced warming - so the variety of simulation studies seems confusing," he said.

"So what we want to present is a good assessment of the issue of predictability; we probably won't provide a solution [to why the near term is hard to predict], but we will provide the scientific basis to explain it."

Active areas of research that are vital for understanding climate change - including the interactions of clouds and dust particles in the atmosphere, and sea-level rise - will receive their own detailed chapters.

Also for the first time, AR5 will take a detailed look at whether some aspects of climate change will lead to transformations of the Earth's land, air and oceans that are irreversible on human timescales.

Impactful agenda

With greenhouse gas emissions set to continue their rise as the global recession eases, there is growing acknowledgement that research on living with climate impacts - adaptation - is equally as important as studying ways of curbing emissions.

Developing countries - particularly those experiencing what they believe to be climate impacts now - are especially adamant that adaptation must secure equal status to mitigation.

Chris Field, who is based at the Carnegie Institution for Science at Stanford University in California, said that AR5 will take this concept on board.

Image caption Climate models are aiming for more "granular" local projections

In order to improve its analyses, the IPCC is adopting a new set of "scenarios" - projections of how the future may unfold, in terms of economic growth, the size of the world's population, policy choices on energy, and so on, all of which affect emissions.

Known as Representative Concentration Pathways (RCPs), the aim is to better integrate data and forecasts on different aspects of the future.

They are also designed to allow for more wide-ranging analyses of policy choices.

"The RCPs... allow us to explore many issues - not only in understanding policy implications, but also how those ramify into things that are as diverse as impacts on distributional equity, questions of justice, or migration," said Dr Field.

"[This is] a wide range of issues where it's been really difficult to figure out what's the climate part vs the societal part."

Interactions between the physical manifestations of climate change and societal issues will be expanded in the third part of AR5, on options for mitigation - a segment that will also include evaluation of what various policy choices mean economically.

"Since the release of AR4, there's been a vast amount of literature on socio-economic aspects of climate change," said IPCC vice-chairman Hoesung Lee.

"And the fifth assessment report will particularly look into this growing literature."

AR5 is due for publication in 2013-4, in four consecutive parts - science, impacts, mitigation and a synthesis - as in previous assessments.

But the procedures and timings have been adjusted with the aim of facilitating co-ordination between groups working on the various aspects - in particular, so that the most recent scientific projections can underpin the analysis of impacts.

The coming months will see the first meetings of lead authors for the first three segments, where they will plot out in more detail how to analyse the vastly increased amount of material on all aspects of climate change.

The Korea conference - the IPCC's annual plenary - ended with the partial adoption of reform measures recommended in the IAC review.

Most of the recommendations, however, are to be discussed by committees over the coming months, with the aim of tying up all the oustanding issues in May.

Richard.Black-INTERNET@bbc.co.uk