Tom Arup, Environment editor
Climate change has been argued about for years, but the latest findings suggest relaxed attitudes towards the phenomenon will result in dangerous consequences for our planet in the very near future.
Early next week, hundreds of scientists will meet in Stockholm's Brewery Conference Centre to put the finishing touches on the world's most important climate change document. It is unlikely the beer will be flowing.
By Friday the United Nations' Intergovernmental Panel on Climate Change will have released the results of its labour - the first part of its fifth major assessment of climate science.
Its last report, released six years ago, delivered a stark message: the climate is warming mostly because of human activity and poses a major threat - especially if global temperatures increase by more than two degrees.
Go beyond two degrees and the planet faces dangerously rising seas, larger drought-affected areas and more frequent extreme weather events, amid other dire projections.
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That report won the group the 2007 Nobel Peace Prize, which the panel's chairman, Dr Rajendra Pachauri, observed would ''be seen as a clarion call for the protection of the Earth as it faces the widespread impacts of climate change''.
Six years on, the fifth report's core findings remain largely the same, only now there is even greater scientific certainty. But already, it is clear the fanfare that greeted the last report is unlikely to be repeated. And so far it is the areas of uncertainty in the report - inevitable when dealing with scientific predictions - that are creating headlines.
To prepare the report, scientists from throughout the world volunteer years of their lives to collate and assess data and modelling results to pull together the report's 3000 or so pages. The report is split into three sections: the first dealing with the physical science, the second and third - due out next year - looking at impacts and ways to cut emissions.
The IPCC does no research of its own, but calls on the expertise of about 830 scientists to draw together evidence from thousands of sources - from ice-core samples drilled out of Antarctica, to ocean temperature records sampled kilometres below the surface - to form the most comprehensive picture of the Earth's climate system.
Scientists who were lead authors on the report gave Fairfax Media a consistent message: the evidence of a warming planet caused by human activity - such as burning fossil fuels and cutting down forests - is stronger than six years ago.
Leaked drafts of the report seen by Fairfax Media reveal it is now ''extremely likely'' - greater than a 95 per cent certainty - that human activity is causing more than half the global warming felt since 1951. It is a small but important increase from the 2007 report's ''very likely'' assessment of 90 per cent confidence.
CSIRO climate scientist Dr Steve Rintoul, a co-ordinating lead author, says ''what is new is we can be more confident in those results, both in how the climate system has changed up to now and also the human contribution to those changes.''
Another lead author, Professor Nathan Bindoff, from the University of Tasmania's Institute for Marine and Antarctica Studies, says the increased confidence is borne from six more years of observations and more refined modelling of several key aspects of the climate system.
He points to losses in ice sheet mass from Antarctica and Greenland, changes in ocean salinity in different parts of the globe and increasing ocean heat content where data has been strengthened and clarified since the last assessment.
''There are some new things that have come along because we have longer records and there are new studies that tell us about human influence on all these aspects of the Earth system - the cryosphere, oceans, snow cover, the lower atmosphere, the upper atmosphere,'' Bindoff says.
''Collectively, that is a lot more evidence than we have had before. It is the comprehensive nature of it.''
Other significant signs include increased confidence that sea levels will rise this century due to faster melting glaciers and ice sheets. Under the worst-case scenario there is now medium confidence that sea level rises could be as much as 81 centimetres by the end of the century, a change that would devastate low-lying communities.
There is more confidence human activity is increasing some extreme weather events - warmer days and nights, and heatwaves - but there is less confidence about changes in the intensity of tropical cyclones.
Despite the increase in confidence, a significant part of public debate has focused on a slowing during the past 15 years in what had in previous decades been the dramatic pace of global warming - and whether that slowdown has implications for the long-term rise in temperature.
Climate sceptics have seized on the slowing to declare warming has paused or stopped, and suggest the danger of letting emissions continue to skyrocket has been exaggerated.
A final draft of the report, seen by Fairfax Media, says the rate of warming across the planet's surface in the past 15 years was about 0.05 degrees a decade - slower than the longer-term warming trend of 0.12 degrees since 1951.
But it does not say warming has reversed. ''Each of the last three decades has been warmer than all preceding decades since 1850 and the first decade of the 21st century has been the warmest,'' the draft report says. The data underpinning the report suggests 12 of the hottest years in modern times have been this century.
Another key area of conjecture is what is known as ''climate sensitivity'': the expected warming that would come from doubling the concentration of carbon dioxide in the atmosphere. The 2007 report projected that this would increase temperatures by between 2 degrees and 4.5 degrees. Drafts of the new report drop the lower end of that range to 1.5 degrees, but maintain the 4.5 degrees high end.
The Australian, in a story quoting the British tabloid The Daily Mail, last week reported the debate over climate sensitivity under the headline: ''We got it wrong on warming, says IPCC''.
But both papers misquoted the last IPCC report, almost doubling its assessment of the observed long-term warming rate and making the comparison with the current report look more stark than it is.
But the pace of warming for the 15 years between 1997 and 2012 has been slower than some of the modelling projections in the 2007 report, which reported a 0.2-degree-a-decade warming rate from 2005 to 2025.
The authors of the 2013 report say the recent slowdown in warming is not significant, that it's the long-term trend that matters. The new report finds that, across land and water, the planet has warmed an average 0.89 degrees since 1901.
''These periods of a decade or more where the rate of warming slows or increases are not unusual,'' Rintoul says. ''If we look back at the temperature record over the last 100 years or so, we see times when the Earth's surface was warming rapidly and times when it was slower, so in that sense it is no surprise.''
What causes decadal changes in the rate of warming? IPCC lead author Professor Steve Sherwood, from the University of NSW, says there are no definitive answers, but points to changes in the uptake of heat in the oceans as one factor. Others include changes in atmospheric aerosol concentrations and solar activity. Sherwood likens decadal changes in warming rates to a cancer sufferer. While they may feel a little better one week compared with the next, it does not mean they are rid of the disease.
Rintoul says the oceans are an important factor in speeding up and slowing down warming in the short term because the more heat stored in the ocean, the cooler the Earth's surface is.
Drafts of the new report say ocean warming has continued unabated and accounts for 93 per cent of the extra heat in the climate system since 1971.
Rintoul says at different times heat stored in the oceans can cycle between higher and lower depths, affecting warming rates on land. He says some heat stored in the oceans may also seep back out, accelerating warming. But it is not clear what triggers this all to happen.
Climate sensitivity is a significant point of debate among scientists working on the report, and some believe wording about the issue could be debated at the Stockholm meeting right up to the release of the report.
Pennsylvania State University climate scientist Michael E. Mann told The New York Times last month he feared the IPCC had been swayed by criticism from climate doubters and had ''erred on the side of understating the degree of the likely changes''. Equally, others say the minor change at the low end of the long-term warming range - down from 2 degrees to 1.5 degrees - is an appropriately conservative response to a genuine debate in scientific circles.
But Sherwood strongly rejects suggestions the changes are an admission of past errors. He returns to his cancer patient analogy: if the diagnosis is the patient is going to die, but there is some uncertainty on exactly when, you do not just throw out the initial diagnosis of death.
The panel's caution this time is likely the result of its experiences during the past six years - notably revelations of three errors in the fourth assessment, including a mistakenly exaggerated claim about future melting in Himalayan glaciers.
While none of these errors was crucial to the central science, it significantly dented the credibility of the UN organisation. Since then it has gone through several reviews, including implementing a system under which almost anybody could sign up to be an expert reviewer of the work. The first section of the 2013 report has received almost 55,000 comments.
Calls for much more radical reform continue. Professor Barry Brook, a senior climate scientist at the University of Adelaide, who is not involved in the IPCC, is among a growing group who say the six-year report process is too slow, too incremental and has outlasted its usefulness. He says the IPCC should issue shorter, more frequent and more targeted reports on specific areas of concern, such as sea ice loss.
One argument in favour of releasing a major report every six years is that it acts as a marker for the fraught negotiations between countries on a global treaty to reduce emissions. But are governments and the community listening? In the West, polls suggest people are less concerned about climate change than in 2007.
The time the last report was released, a Bureau of Statistics survey found 73 per cent of Australians were concerned about it; four years later it had fallen to 57 per cent.
ANU political scientist Professor Ian McAllister says the global financial crisis played a major role, focusing people more on short-term economic security over issues like the environment.
''You saw before the financial crisis people were more likely to rate the environment as a priority issue,'' he says. ''Since then people are more concerned about the economy, job security, things like that.''
Ultimately nervous climate change observers hope debates about sensitivity and short-term warming trends do not distract from the main points of the report or will be used by some governments to reduce their ambition to cut emissions.
After all, there is a significant sting in the tail of the report.
For the first time the IPCC has included an estimate of the total amount of carbon dioxide that can be emitted into the atmosphere after pre-industrial times and still maintain a good chance of keeping global warming below two degrees.
At least half this carbon budget was already used up by 2011. And it does not include the impact of other greenhouse gases, such as methane and nitrous oxide. If it did, the budget would be much tighter.
To keep within even this generous two-degree budget, the draft report suggests the world needs to make radical and swift cuts to greenhouse gases along the lines of the toughest future emissions reduction path considered by the IPCC.
That would mean an average cut to emissions of 50 per cent by 2050 on 1990 levels. And by the end of the century, instead of adding carbon dioxide to the atmosphere, there is a good chance the world will need to find ways to draw it out.
Instead, work by lead author Dr Josep Canadell, from the CSIRO, and fellow colleagues at the Global Carbon Project, has found the world is tracking along the highest emissions path being considered by the IPCC. If this continues then, according to the draft report, the average global temperature would increase 2.6 degrees to 4.8 degrees by century's end.
Canadell says even if movements in climate sensitivity have bought the world, at best, a little time to avoid dangerous climate change, it is no reason for celebration.
''We should certainly not relax at all,'' Canadell says. ''If anything, the two degrees [target] will be very difficult, if not impossible, to reach. And two degrees is just the maximum we can afford.''
Hardly cause to raise a beer.
At a glance
The next report of the UN Intergovernmental Panel on Climate Change is in three parts. Part one, released on Friday, deals with the physical science. Part two (effects) and part three (ways to cut emissions) are due next year.
The core finding is that evidence human activity is warming the planet is stronger than six years ago.
The pace of global warming during the past 15 years has been slower than in previous decades. Sceptics claim warming has paused or stopped, but the report says the slowdown does not change long-term trends.
