Dr Vicky Pope, Climate Science expert
Why is everyone so surprised when we say that climate science is uncertain? All areas of science progress through constant challenge and exploration of the boundaries of uncertainty - what is important is to be able to evaluate that uncertainty. Climate science is no different.
The facts about global warming are not a question of belief, just as the IPCC report is not a 'Green Bible'. Substantiated facts emerge from carefully considering all the evidence. The various assessment reports of IPCC provide a snapshot of that evidence at the time they are produced.
I know from colleagues who have been involved in IPCC that, for the most part, authors go to extraordinary lengths to present all the relevant evidence. For this reason the IPCC report contains some contradictory statements and lengthy discussion of the complexities and uncertainties. The authors then debate each contentious issue, and summarise the key findings. Everything from the smallest detail to the most general top-level statement is open to review and challenge by anyone. In addition, the summary for policymakers is agreed by governments.
The resulting top-level statements need to be extremely robust. However, because of the uncertainties in this rapidly evolving area of science they are also, inevitably, very general and can look rather vague to the lay-reader. The temptation then is to cherry pick statements from the main body of the report that happen to suit the point you want to make. However, when taken out of context, such statements should not be seen to have the weight of IPCC behind them, but rather they represent the original source material.
While all this is true for most of the 3,000 pages of the IPCC reports, it is now clear that there were errors and misjudgments in some sections that were not corrected. It is clear that IPCC needs to improve its processes to avoid including statements that are not well supported. It also needs to find a better way of dealing with emerging errors.
However, the overwhelming evidence for global warming remains intact and the last IPCC report (AR4), published in 2007, included the statement that "Warming is unequivocal and very likely (more than 90% probability) due to man's activities." Since then this has been reinforced by further evidence of global warming affecting heat in the ocean, rising Antarctic temperatures and the shrinkage of Arctic summer sea-ice.
Basic physics tells us that increasing greenhouse gases cause global warming - and we are likely to pay a heavy price if we keep emitting them at current rates.