Global-warming deniers jump for joy every time there’s even a brief dip in generally upward trends
One of the more peculiar aspects of global-warming denialism is that its apostles seem not to understand that the trend is not relentlessly upward.
As the chart above makes clear, the long-term upward trend has brief downward dips. But your typical right-wing zealot sees every such dip as proof positive that global-warming theories are a hoax perpetrated by wacko environmentalists.
The latest example of this phenomenon arises with a transitory change in the long-term melting of Arctic ice. THIS REPORT from one British newspaper debunks the nonsense peddled by two rival newspapers:
When it comes to climate science reporting, the Mail on Sunday and Telegraph are only reliable in the sense that you can rely on them to usually get the science wrong. This weekend’s Arctic sea ice articles from David Rose of the Mail and Hayley Dixon at the Telegraph unfortunately fit that pattern.
Both articles claimed that Arctic sea ice extent grew 60 percent in August 2013 as compared to August 2012. While this factoid may be technically true (though the 60 percent figure appears to be an exaggeration), it’s also largely irrelevant. For one thing, the annual Arctic sea ice minimum occurs in September – we’re not there yet. And while this year’s minimum extent will certainly be higher than last year’s, that’s not the least bit surprising. As University of Reading climate scientist Ed Hawkins noted last year:
“Around 80% of the ~100 scientists at the Bjerknes [Arctic climate science] conference thought that there would be MORE Arctic sea-ice in 2013, compared to 2012.”
The reason so many climate scientists predicted more ice this year than last is quite simple. There’s a principle in statistics known as “regression toward the mean,” which is the phenomenon that if an extreme value of a variable is observed, the next measurement will generally be less extreme. In other words, we should not often expect to observe records in consecutive years. 2012 shattered the previous record low sea ice extent; hence ‘regression towards the mean’ told us that 2013 would likely have a higher minimum extent.
The amount of Arctic sea ice left at the end of the annual melt season is mainly determined by two factors – natural variability (weather patterns and ocean cycles), and human-caused global warming. The Arctic has lost 75 percent of its summer sea ice volume over the past three decades primarily due to human-caused global warming, but in any given year the weather can act to either preserve more or melt more sea ice. Last year the weather helped melt more ice, while this year the weather helped preserve more ice.