Extreme weather has dominated world headlines recently, with a record-smashing heat wave in Russia as well as deadly flooding in Pakistan that may rank as that country's worst natural disaster. Here at home, we've endured a sizzling summer, and NOAA announced last week that 2010 is still on track to be the warmest year on record (although La Nina may knock it back a rank or two).
The relationship between global climate change and these extreme events is complex in that climate change did not specifically cause them to occur, but likely did influence them, perhaps in significant ways. An article in Sunday's New York Times clearly laid that out, and (as I have previously noted), Jeff Masters of Weather Underground has provided uniquely in-depth coverage of possible links between climate change and extreme weather
Stu Ostro, senior meteorologist for The Weather Channel, is a rare breed of meteorologist who is increasingly focused on the intersection between climate and weather. A former climate change skeptic, he has compiled a lengthy presentation showing changes in weather patterns that he believes may be related to climate change.
In an email interview during the weekend, Ostro shared his thoughts on climate change and extreme events, and what has convinced him that climate change is now manifesting itself in daily weather patterns.
Andrew Freedman: As a meteorologist, you've been noticing changes in certain weather patterns and the frequency/characteristics of extreme weather events in recent years. What are some of the changes that you've seen, and how do you think they may be related to global climate change?
Stu Ostro: I have been closely looking at weather charts since I started college in 1976, when I first gained routine access to them (that was long before the Internet!). By coincidence, that's the year after which globally-averaged temperatures commenced a significant warming trend. Fast forward to the most recent decade. I was noticing that something had changed: the 500 millibar heights seemed to be getting higher. In other words, the pressure a few miles up was rising, at a level which is important to meteorologists and whose charts we routinely analyze. It was like an irresistible force was exerting pressure (no pun intended) on the atmosphere.
My epiphany came a few years ago, when I started looking at the data going back to the 1970s and found that the long-term trend of average annual pressures at that and other levels aloft was indeed significantly upward, especially in the Northern Hemisphere, during the same time that average temperatures had risen significantly. At the same time, what meteorologists call the "1000-500 millibar thicknesses" had demonstrated a similar trend. The depth of that layer of the atmosphere was increasing, and that's directly related to the mean temperature of the layer.
And what also seemed to be happening was that not only was the average pressure aloft rising, that was manifesting itself via particularly strong and/or persistent individual (day-to-day, week-to-week) ridges of high pressure aloft. They in turn are associated with intense heat waves in the summer and unusually warm stretches at other times of year. Furthermore, in tandem with those strong ridges there have been a lot of notable "cutoff lows" (low pressure systems aloft that have been cut off from the main jet stream), and they are often associated with precipitation extremes as well as topsy-turvy temperature patterns.
AF: What do you tell people who ask questions such as, "is this heat wave because of global warming," or "is this flood because of global warming?" The issue of attributing extreme events to climate change is very complex, and I know you've worked to more clearly communicate what is and isn't known.
Ostro: Yes, the system is indeed very complex, and not every weather event can or should be attributed to climate change. But that doesn't mean that no weather events can be linked to it. This was my second epiphany. On December 4, 2006 I went over to the dark side, sending an email to some of my colleagues at TWC which included, "I can no longer accept the mantra of 'individual weather events can't be connected to global warming,' much less be the vocal proponent thereof as I used to [be]."
If I'm asked about a particular event, I objectively look at the data and the pattern and the impacts, and evaluate the degree to which I'm willing to connect that event to the large-scale warming.
AF: Whenever I write about how climate change may already be altering weather patterns, and the changing the nature of extreme events, I get a lot of push back from people who accuse me of mistaking weather for climate, or opportunistically crying "global warming" every time the weather does something strange. Have you had that reaction from people, and how do you respond to such criticism?
Ostro: I've given talks at workshops and conferences where the previous speaker(s) made it a point to highlight the difference between climate and weather, and I've made it a point to highlight the connections. I'm doing everything I can to get people to break out of the paradigm that climate and weather are separate entities. Aside from the two being intimately and inexorably linked, like the brain and the heart, or a book and its chapters, with weather and climate there's a continuum of scales of time and space.
AF: What is the quintessential example of a recent extreme event that you think was especially consistent with climate observations and projections? In other words, what event really stands out in your mind when you think about a climate change-related extreme event?
Ostro: The obvious one is the Russia heat wave, which has been extraordinary in its intensity and duration, and associated with an exceptionally persistent and strong ridge of high pressure aloft - the same signal as, but even stronger than, the one which was present during the peak of the 2003 Europe heat wave. And this time the heat and ridge were related to a persistent downstream trough just west of Pakistan from about July 20 through the first few days of August, which in turn was associated with the exceptional rainfall and flooding there. At times that trough evolved into a cutoff low, like what I described earlier.
AF: How would you characterize the views within the meteorological community, and specifically the TV meteorology community, toward possible links between climate change and extreme events? Do TV meteorologists tend to downplay potential links, in your opinion? It seems to me that much more work is being done within the climate change community to look for relationships between long-term climate change and shorter-term extreme weather events, despite the fact that short-term weather is in the meteorologists' domain.
Ostro: There have been surveys done which document that a lot of skepticism exists amongst TV weathercasters/meteorologists, and the operational forecasting community in general, about anthropogenic global warming (AGW), both the seriousness of the warming and the amount of the human role. That's been my anecdotal observation as well. Such doubt also undoubtedly exists about linking extreme events to climate change, regardless of cause, but I don't know whether it's more or less than about AGW in general.
AF: You've been documenting extreme weather events for some time now, and have accumulated a ton of data on how the warming climate may already have altered certain atmospheric characteristics. What do you hope to do with this data, and what has the reaction been among people who have seen your presentation?
Ostro: There has been an extreme, and extremely interesting, split in the reaction. Of course hard-core "skeptics" have reacted with cynicism (more so to my blogs than my presentations). I've been called a lot of names, and lately the critics have gotten quite creative, in one case a blogger dubbing me "Mr. Ostroass."
But interestingly, quite a few meteorologists who had previously been highly skeptical about anything to do with global warming have had an enthusiastically positive response. Some of that may be because I'm "speaking their language," i.e. communicating to them by way of weather events and data and charts to which they can relate. I've also received feedback that they've appreciated that I haven't "talked down to them" like they have perceived some climate scientists to have done.
Speaking of climate scientists, I experienced that attitude myself from a well-known one upon seeing an early version of my documentation back in 2005, but I did not let that discourage me. Since then, I have received a lot of encouragement from some top climate scientists, though others have still had a rather chilly reaction. My sense is that for them, they won't take what I've done seriously until it has been subjected to the rigor of a formal analysis followed by the peer review process and then publication in the traditional scientific literature. With the help of collaborators, that's what I hope to do.
The views expressed here are the author's (and interview subject's) alone and do not represent any position of the Washington Post, its news staff or the Capital Weather Gang.