Report: The Case for Global Warming Stronger Than Ever - part 2.

.. contd. from part 1....

The question from critics remains: how can we be sure that global warming isn't just a natural phenomenon ?

Scientists have not done a good job of communicating how they distinguish human versus natural influences, says Heherl. The answer lies in climate models - massive computer simulations that allow the scientists to project climate effects in various scenarios, including those in which humans do not emit any greenhouse gases at all. "We go out of our way to check out other explanations - by asuming it's all explained by solar activity, or by solar activity plus volcanoes, or by combinations of any of the other natural forcings known to affect climate," says Haherl.

According to the models, none of those combinations  can produce the climate patterns currently being observed in the real world. Add the greenhouse gases that we know humans are generating (and which we've known since the 1800s tend to warm the Earth, all other things being equal), and the simulations finally come close to matching the real world. Its possible, albeit far-fetched, that the simulations are defective. It is even less possible that all of them (and there are many) are defective in the direction of overstating humanity's contribution to warming.

Again, none of the evidence adds up to absolute certainty, a rare commodity in any field of sciences. U.N. Secretary General Ban Ki-moon has announced that an independent panel of scientists, representing national science academies from around the world, to review the IPCC's research procedures - an effort to account for the 2007 report's mistakes, for which the IPCC has come under hard criticism. But while the U.N. group may benefit publicly from more transparency, it won't change the fact that more than 99% of the scientific details in the 2007 report have already withstood the most intense scrutiny. The fact that climate change evidence that was "very likely" a few years ago has now been declared likelier still by the comprehensive Met Office report suggests that the evidence for human-caused climate change is getting better all the time.

Source: Michael D. Lemonick, TIME/CNN