for National Geographic News
How much Earth's climate will change due to global warming is inherently unpredictable, a new study argues.
The claim has big implications for the way decisions will be made that affect the climate over the coming century, some researchers say.
Scientists have been trying to pin down how much the world will warm up over the coming centuries if people continue emitting carbon dioxide (CO2) and other greenhouse gases into the atmosphere.
(Learn how global warming works.)
Experts often make their estimates by using computer simulations to gauge how average temperatures would eventually change if CO2 emissions were to double their preindustrial levels.
Various models agree that this doubling would likely raise Earth's temperature by 5 Fahrenheit (3 Celsius) over the coming centuries.
But there's still a fair chance the increase could be much more than this.
For the last three decades, climate researchers have estimated that there's a one-in-three chance that the warming from a doubling in CO2 would be more than 8 Fahrenheit (4.5 Celsius).
There's also a 5 percent chance of much more drastic warming, around 12 Fahrenheit (7 Celsius), the models suggest.
"You'd hope that if you throw more computers and people at the problem, your confidence would increase," said Gerard Roe of the University of Washington, who led the new study.
"[But ] this range in uncertainty hadn't been going down over the last 30 years."
Roe's team's research, published today in the journal Science, provides a simple explanation as to why.
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