The last time the world's climate scientists produced a major report, it had the effect of ending the scientific debate about whether man-made climate change was a real phenomenon.
This time around they hope to provide the world's governments with more useful detail about what they can do about it.
Due to be published in October 2014, the Intergovernmental Panel on Climate Change's (IPCC's) Fifth Assessment Report is expected to be the most detailed on climate change ever produced, and for the first time answer important questions about how each region will be affected.
It will also include another first: a chapter on ocean systems, describing how the rise in greenhouse gases in the atmosphere will affect the marine environment and the ocean's ability to supply food.
At the request of several governments, it will also review current knowledge on geo-engineering, a group of methods to reverse warming through large-scale human interventions.
While proponents say such huge interventions are needed to avert catastrophe, others fear they have the unpredictable potential to cause more harm than good.
Compiled by 840 leading scientists, the report will review all currently available scientific literature on climate change.
It has been a long time in the making. Work began in 2008. It takes so long, according to the panel's vice chairman, Prof Jean-Pascal van Ypersele, a Belgian physicist and climatologist, because "a lot of attention is given to the review process" - that is, the process of checking the scientists' work.
The first review stage by scientists is complete. Between now and next May, governments and non-governmental organisations have their chance to take part in the review.
That is no small task. The authors of the fourth report reviewed and responded to about 90,000 comments.
Once governments have submitted their comments, an abridged version - the "summary for policy-makers" - will be submitted for approval at a plenary session between those policymakers and scientists.
The summary will be a 10 to 20 page recap of the main points of the report, which is likely to weight in at about 1,000 pages.
"Some governments do not like what they find there but that is not sufficient to have it changed, if there are no good scientific reasons to do so," said Prof van Ypersele.
"Their comments are treated like any other comments. They need to come with specific and scientific comments."
Comments are allowed if scientific language is difficult to understand or if statements need to be qualified with nuances.
But changes to the text must be scientifically justified. Governments cannot remove sections because they don't like the science.
"There are a few limited changes," Prof van Ypersele said. In past reports, a "few dozens of lines" were changed, but "never ... a change affecting a scientific conclusion".
The summary is approved by consensus, a process that usually takes three to four days and at least a night of talks.
"The dialogue is sometimes intense," says Prof van Ypersele, "but scientists always have the last word."
The close attention of governments and experts is warranted. The impact of past reports on international policy has been huge.
The last one, published in 2007, stated that it was "very likely" - with a probability of at least 90 per cent - that most warming in the past 50 years was due to the increase in the concentration of greenhouse gases in the atmosphere as a result of human activity. That statement had the effect of ending serious debate about whether warming was happening or not. And for that, the IPCC was awarded the Nobel Peace Prize in 2007, sharing it with the US environmental campaigner Al Gore.
Tanzeed Alam, policy director of the Emirates Wildlife Society-World Wide Fund for Nature, described it as a "landmark".
"Many policymakers are now accepting climate change is happening and are looking for ways to tackle it," Mr Alam said.
With the fourth report having settled the question of whether climate change was happening, the fifth will for the first time include detail that will make it of far more practical use to governments - information on expected changes and environmental impacts in each region.
That, says Prof van Ypersele, is something policymakers are "very often, very much interested in".
Scientists use complex computer simulations to predict future changes in climate. But until recently, the models were not evolved enough to provide regional detail.
"The difficulty is that for many climate parameters, the uncertainties are larger when you look at results on a regional basis," said Prof van Ypersele.
For example, it is well known that with expected warming, the world will see more rain on average. "You can provide that conclusion with confidence," he said.
But on a regional level, rainfall is not only influenced by temperature and subsequent evaporation, but also by patterns such as winds and vertical air movements.
"For many regions of the world, not even the sign of the change [in precipitation] is known yet. With the scientific progress made in the understanding of the climate system and the progress in modelling, it has been possible to improve the quality of regional information."
For West Africa, for example, little is known about how future changes in climate will affect rainfall. But the question is particularly important for a region already affected by severe droughts.
More detailed information is also needed about expected changes in the Middle East. Any changes will have an obvious impact on the UAE, which is already one of the most water-stressed countries in the world.
Scientists are also looking at parameters that are less publicised than rainfall but can nonetheless have crucial importance in some regions.
The frequency of agricultural droughts, for example, can have a profound impact on drought-vulnerable countries. "It is a little more abstract, but it is extremely important," said Prof van Ypersele.
The regional information will be contained in an "atlas" that will show the evolution of many climate parameters.
From a UAE perspective, said Mr Alam, even something as basic as future temperature can be hugely significant in a country where energy demand soars in summer due to the need to cool down buildings.
"Global scientific reports have already helped us persuade local policymakers of the need to act," said Mr Alam. "Anything that has more concrete data can only help further."
