By Tom Yulsman
With astonishingly high temperatures for this time of year persisting over the Central and Eastern United States — including nighttime “low” temperatures that exceed the normal highs — it’s only natural to wonder what role climate change might be playing.
As Andrew Freedman of Climate Central put it Tuesday:
“In a long-term trend that has been found to be inconsistent with natural variability alone, daily record-high temperatures have recently been outpacing daily record-lows by an average of 2-to-1, and this imbalance is expected to grow as the climate continues to warm. According to a 2009 study, if the climate were not warming, this ratio would be expected to be even.”
Of course, it shouldn’t be any surprise that the blogosphere has lit up with denials that any such link between the record-breaking warmth and climate change exists. And in one very narrow sense, they’re right. That’s because the immediate cause is a huge north-to-south kink in the normally west-to-east flowing jet stream. This kink in turn has caused a large ridge of high pressure to become stuck over the Midwest and East, bringing unprecedented warmth.
As Jeff Masters, a meteorologist with Wunderground.com, reports in his blog, northern Michigan has recorded temperatures in the 80s — about 40 degrees above average for this time of year. International Falls Minnesota, sometimes called the “Nation’s Icebox,” has experienced unheard of temperatures pushing 80 degrees during the day, and lows that have failed to dip below 60 at night.
A balmy March evening in northern Minnesota? Really?
“I’ve never seen a station with a century-long data record have its low temperature for the date match the previous record high for the date,” Masters wrote in his blog.
But beyond the immediate cause, the rising concentrations of greenhouse gases in the atmosphere are raising the odds of such extreme warm events occurring. The situation is akin to a baseball player on steroids, as a now renowned video from the National Center for Atmospheric Research has demonstrated so convincingly.
But if the headlines in Marc Morano’s Climate Depot aggregation website this past Monday were any indication, that’s not at all how climate skeptics are seeing it.
2012 is 0.6C Cooler than 2010 So Far, shouted one headline.
Global Temperatures have plunged .56°F since An Inconvenient Truth was released, said another.
No Warming For 17 Years, still another claimed.
The overall argument of these and other posts is that despite a toasty spell in parts of the United States, warming has stopped globally — and lately, the globe has actually been cooling.
Well, if you love cherry pie, take a nice big bite of these claims, because you can find evidence to support them. But if what you want is a full course of the truth, the claims simply are not warranted by the evidence. Not even close.
The interactive web site, Woodfortrees.org, is an excellent tool for testing out claims about global temperature trends. As described on the home page, “This site hosts some C++ software tools for analysis and graphing of time series data, and an interactive graph generator where you can play with different ways of analyzing data.”
And when you play with the data on the site, it becomes evident that it is quite easy to show, as Paul Clark, Woodfortrees’ creator puts it, that the global average temperature is falling, or static, or rising, or “rising really fast!” All you have to do is pick your cherries — meaning your starting and ending dates — appropriately.
Here’s a chart he created that demonstrates this quite clearly. The y-axis is a measure of how temperatures (measured in C) have departed from the long-term average.
The chart uses satellite data on the temperature of the lower portion of the atmosphere compiled by researchers at the University of Alabama, Hunstville. Of the four global temperature series that are typically used to keep track of how the climate is changing, this one tends to return the lowest temperature anomalies. That makes it a favorite of climate change skeptics. And what does it show?
From 1978 (when this satellite record began) to the present, warming is unequivocally evident (the green trend line). But if you choose other starting and ending points, you can make a case for different trends. In other words, if you do some cherry picking, you can pretty much show whatever you want.
And that’s precisely what those skeptical headlines represent: cherry picking.
What difference does it make if 2012 has been cooler than 2010? In the chart above, it’s also evident that 2011 — an exceedingly warm year on average — was nevertheless cooler than 1998. Who cares? What does any of this have to say about long-term climate change? Your guess is as good as mine.
What of the claim in one of the stories mentioned on Marc Morano’s site that there has been no warming for 17 years? Putting aside that rather strange time span for a minute, the gently rising green trend line of temperature change over the past 17 years in the chart below shows this is not true.
Even more important, though: Watts up with that 17-year period? If it seems awfully arbitrary, that’s because it is. Were I to choose, say, 1992
— the year that countries first joined in the United Nations Framework Convention on Climate Change — I would get a completely different result: a warming trend that is pretty obvious (the magenta line in the graph).
As for cooling since 2005, another of the skeptics’ claims, it is actually true for all but one of the main global temperature series. But this is just another case of seeking out the sweetest cherries for making a tasty argument pie — not to find out what’s actually going on with the climate.
It may well be true that warming of the lower atmosphere has slowed or paused for a spell. But that does not necessarily mean warming of the entire Earth system — oceans included — has stopped.
Recent research has been filling in details of how the oceans are actually continuing to sop up some of the heat produced under the greenhouse conditions we humans have enhanced. And the research helps to explain “hiatus” periods in the warming of the atmosphere.
Moreover, Norman Loeb of NASA’s Langley Research Center, and a group of colleagues, were recently able to complete a more accurate accounting than previously possible of just where solar energy was winding up in the Earth system — including the large portion known to get socked away in the oceans. In a paper published in Nature Geoscience, they concluded that over the past decade, the overall Earth system has been steadily accumulating energy at a rate of about half a watt per square meter.* A significant portion has been getting socked away in the oceans. And while that may sound like a good thing, that heat isn’t simply disappearing; over time it will contribute to warming of the atmosphere.
It’s also important to realize that natural variation in the climate system hasn’t simply stopped. It still exercises a powerful influence — which is a significant reason why graphs of temperature change over the course of decades are jagged and irregular. There are few if any doubts that human activities are pushing strongly on the climate system, causing the trend-line of global average temperature to rise, overall, in the long run. At the same time, however, that system is quite complex, and so it should be no surprise that natural variation can push back quite effectively at times.
But over the very long run, the picture has been pretty clear: Humans are winning — as this March’s extraordinary weather suggests.
*Correction: The original version of this post mistakenly stated that this was a rate of about five watts per square meter. Updated March 25 at 7:00 p.m.