At WSJ:
The single most important benchmark underpinning this week’s talks in Paris on climate change—two degrees Celsius—has guided climate-treaty discussions for decades, but some scientists question the validity of the target.Okay, so far so good. But then you get this doozy:
Many researchers have argued that a rise in the planet’s average global air temperature of two degrees or more above preindustrial levels would usher in catastrophic climate change. But many others argue that is a somewhat arbitrary threshold based on tenuous research, and therefore an impractical spur to policy action.
“It emerged from a political agenda, not a scientific analysis,” says Mark Maslin, professor of climatology at University College London. “It’s not a sensible, rational target because the models give you a range of possibilities, not a single answer.”
Policy makers tend to assume the two-degree target expresses a solid scientific view, but it doesn’t. The exhaustive reports published by the United Nations Intergovernmental Panel on Climate Change are considered to be the most comprehensive analysis of the science of global warming. Yet the two-degree limit isn’t mentioned in a single IPCC report.
Still, many scientists are willing to back the goal because they see it as giving policy makers a clear-cut target to shoot at in the fight against global warming...
Most climatologists agree that the earth is getting warmer and that the emission of greenhouse gases is the main driver of this change. But the question of when a catastrophic tipping point might be reached is up in the air...Um, greenhouse gases are not the main driver. Frankly, we don't know what the main driver is. It could be anything. We're talking about the whole damned earth and the freakin' solar system. The number of possible variables is staggering.
But Professor Maslin's right: It's a political agenda, not a scientific program.
But keep reading.
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