Global warming - sometimes a confusing subject. What's opinion, what's fact? Who do you believe? There's general agreement that the globe has warmed a degree or so over the last century. The question is - what's the cause?

There's an international panel of climate scientists, sponsored by the United Nations, with the responsibility of presenting an unbiased, unhyped account of global warming. In their last report, in 1995, they stated that "the balance of evidence suggests a discernible human influence on global climate." That is to say, they're not completely confident that humans are to blame. But in the years since, evidence has mounted pointing to human activity as at least partly the culprit for the warming.

Their updated report, to be released later this year, states "there has been a discernible human influence on global climate." It is no longer a suggestion. If those words hold up under further review, they would be the strongest official pronouncement yet that human-induced warming is real.