What do last year's abnormally warm year worldwide and Barry Bonds' home run record have in common?
They both may need an asterisk to signify that someone has been cooking the books.
When baseball slugger Bonds broke Hank Aaron's home run record last year, many in the baseball world sought to add an asterisk to his home run total to indicate the influence that steroids use may have had in powering all of those baseballs over ballpark fences. For Bonds, the asterisk would become a modern day "Scarlet Letter."
Along similar lines, in the climate arena one idea to signify the influence of man made climate change is for climatologists to attach an asterisk to record warm periods, such as 2007, which according to NASA tied with 1998 for the second warmest year in a century. Such an asterisk would note the influence that human emissions of greenhouse gases - Mother Nature's steroids - may have played in boosting the temperature to that level.
In both Bonds' case and with the weather, the asterisk is more accurately applied to a statistic of a longer period than an individual event. While the performance enhancing benefits of steroids may increase the odds of hitting a home run, it's difficult, if not impossible, to attribute a single home run to steroids use. It could just as easily result from "natural" factors such as Bonds' innate skills, weight lifting regimen, practice routine, etc. After all, Bonds hit home runs before he allegedly used steroids.
But over the course of a season and a career, the increasing odds of hitting a single home run from steroids should compound, so it's no stretch to attribute a portion of Bonds' home run totals to steroid use, especially since his home run numbers surged late in his career, which was exactly when he allegedly took the juice.
Extending this train of logic to weather, a single Barry Bonds home run is like a single record warm day, such as occurred last Wednesday when the temperature climbed to 74 degrees in Washington. While such record warmth might seem suspicious in light of the science linking warming with greenhouse gas emissions, the fickle nature of day-to-day weather prevents making such a direct connection.
Climate scientists point to increasing concentrations of greenhouse gases as the cause of long-term warming trends. The data showing the spike in such gases as carbon dioxide and methane are striking, and help drive home the point that the atmosphere today when new records are being set has a far different composition from that of several decades ago.
According to the United Nations Intergovernmental Panel on Climate Change (IPCC), global greenhouse gas emissions increased by 70 percent between 1970 and 2004. There is now more carbon dioxide and methane in the atmosphere than has been present for at least the past 650,000 years. These greenhouse gases, the IPCC found, have helped drive global average surface temperatures upwards by about one degree Fahrenheit during the past 100 years, especially within the past two decades.
These greenhouse gases may have increased the odds of having that warm day, but as with the lone home run, it's next to impossible to determine whether that daily record high was due to greenhouse gas emissions, entirely natural factors such as the presence of a Bermuda High, strong warm front, or myriad other weather variables that influence day-to-day variations.
In fact, the storm that brought the deadly tornadoes to the mid-South and the mild air to D.C. most likely would have occurred if there were fewer molecules of carbon dioxide in the air -- despite John Kerry's suggestion otherwise..
According to the Associated Press, if there was any longer term climate cycle at all to blame for the storm, meteorologists suspect the periodic ocean-atmosphere climate cycle of La Nina, not global warming.
There were warm days before the atmosphere was juiced with man-made greenhouse gases. But as the years trend warmer and warmer due to more and more warm days at the same time as greenhouse gases build-up, attributing warm years to greenhouse gases, at least in-part, becomes more and more defensible.
So, in my view, an asterisk for long-term climate records is justified, but not for daily weather records and I'm happy about that, on a more selfish level.
I get a great deal of satisfaction by knowing that the weather I'm experiencing on a particular day is going into the record books because it beat out a similar occurrence in, say, 1934. Then I can say to a friend: "Hey, it hasn't been this warm on this day since 1934! Crazy, right?"
But if a climate change asterisk were added, I'd have to say something that is far more confusing, irritating, and not altogether accurate based on current climate science.