In advance of the report, United Nations Secretary-General Ban Ki-moon traveled to Antarctica last week to get a first hand look at the effects of global warming on the polar ice caps.
It is scientific fact the world has warmed a degree and a half in the past 150 years.
You still find people who question whether man caused it, but not members of the Intergovernmental Panel on Climate Change.
They have published thousands of pages this year documenting the scientific basis of global warming, while projecting its impact, and looking at solutions.
Dr. Stephen Schneider from Stanford University is one of the authors.
Before leaving for the meeting in Valencia, Spain, he took time to explain how representatives of 140 nations reach their conclusion.
It is the nature of politics that nations look out for their own interests, even trying to solve the problem of a warming planet.
"The governments are involved in telling you what they think is important. Naturally, you will get different views," said Schneider.
And so, another round of negotiations for Dr. Stephen Schneider of Stanford University.
Every IPCC report, he says, has been a matter of spin, balancing the financial interests of nations that produce oil or burn coal with scientific facts.
"So these countries are always in conflict over how the language should express the degrees of alarm," said Schneider.
According to early indications, Saturday's Governmental Policy Guide and Summary will declare global warming to be here and getting worse.
Those are stronger words than ones we heard last spring.
"At the global level, there is a manmade climate signal coming through on plants, animals, water, and ice," said Peter Schwartz, IPCC analyst in April 2007.
Even today, the IPCC has scientific critics, who describe the warming as part of a natural 1500 year cycle.
The great unknown is how much faster or further carbon dioxide emissions will drive those temperatures.
Worst case scenarios predict melting ice packs, drought, heat waves, and more serious storms.
Thursday, a Category 4 cyclone killed at least 500 people in Bangladesh.
No one blames that on global warming, but scientists look at trends.
For that reason, the report will urge caution.
"What we don't know is are we going to be moderately unlucky, and warm up two to three degrees more? Or catastrophically unlucky and warm up five or ten? We can't tell you that, now. That's the gamble we're taking with the earth," said Schneider.
You might wonder where the American government stood in terms of describing the warning - strong or moderate?
Well, according to be BBC, with all the oil we use and coal we burn -- moderate.