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By Stu Ostro
Senior Meteorologist, The Weather Channel

I used to be very "skeptical" about global warming, unconvinced that humans had anything to do with it or that it was affecting the weather. But then that changed. In fact, a few years ago I was highlighted by The Week as being one of six "high profile defectors," climate change "doubters" having lost one of their "leading lights."

What's up with that? Did I suddenly switch from conservative to liberal? No, in fact I consider myself politically independent. I have voted for Republicans, Democrats and Libertarians. (I've either now assuaged everyone's concerns or irritated everyone, or both!)

Did The Weather Channel pressure me to change my point of view on global warming or what I communicate about it? Nobody at The Weather Channel, its owners or its advertisers has ever done that. I come to my own objective conclusions, and that will never change. Skepticism is a fundamental part of the scientific process, and healthy when in that vein. I continue to look at data with a skeptical eye. However, skepticism is not constructive when it becomes overwhelming and results in being closed-minded and only seeing what you want to see.

So, what convinced me?

I Flew

When my parents, may they rest in peace, took me on my first flights back in the 1960s and 1970s, I recall the atmosphere being very clear once getting above the low-level haze layer. Now, there's usually a milky gook visible, even within a fresh clean cold air mass in winter, not just a stagnant one in August.

Image credit: Stu Ostro

Greenhouse gases cannot be seen by the naked eye, but I thought, "If there's all this stuff in the atmosphere that I can see noticeably more than 30 years ago, maybe there's something to that carbon dioxide thing."

I Became More Open-Minded to Climate Science

I am a meteorologist, not a climate scientist. I hadn't ever read any peer-reviewed scientific literature on climate change. Why bother? I was busy forecasting the weather, didn't have much spare time, and anyway all this global warming business was bunkum.

Click to enlarge.
Image credit: Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate, Journal of Climate, 2004.

Then I saw these graphs from a paper which was a bellwether of climate change research published in the Journal of Climate in 2004, showing what temperatures should be doing if only driven by natural variability, vs. what they were doing, and how neither the sun nor volcanoes nor anything else could account for the deviation, but greenhouse gases could. Yes, these analyses are model-based, and we all know model forecasts of tomorrow's weather can be wrong (such as "Noquester"), but that's model apples to model oranges, and this paper was written by some of the top scientists in the world, and I could not refute their data or methodology or conclusions.

Something Ain't Right

And last but not least...

As a meteorologist and a weather forecaster, I was used to observing extremes, and they have existed for as long as there has been weather on this Earth, which as Carl Sagan would say is billions of years. Then, about 10 years ago, I started noticing that something ain't right. That the pressures aloft—technically "geopotential heights"—at every opportunity seemed to be rising higher in a given location and at a given time of year than they were at the start of my career about a quarter century prior.

Indeed, historical analyses indicate a clearly visualized correlation between globally-averaged surface temperatures and those pressures up in the atmosphere (in the first graphic below, specifically 500 millibar heights, a few miles above the surface of the Earth). That is consistent with basic meteorology, as there is a relationship between the "thickness" of a given layer of the atmosphere and its mean temperature.

Image credit: Stu Ostro
Cross-section of the change in geopotential heights from the last decade with years of below-average global temperatures, ending in 1976, to the most recent decade. Image credit: NOAA

And then came the 2005 hurricane season. There was a focus on the extremity of it being primarily a result of above-average water temperatures in the tropical Atlantic and Gulf of Mexico, but the water there is typically warm enough during any hurricane season to support strong tropical cyclones, yet most outcomes are not like '05, including other years when water temps have been well above average.

So I looked to the atmosphere, which is more important in and around tropical cyclones for their formation and intensification than water temperatures below them, to see if there was anything out of the ordinary, and what I found sent my eyebrows up my forehead and dropped my jaw.

200 millibar geopotential height anomalies during the peak of the 2005 hurricane season from August 24 (date when Katrina became a hurricane) through October 24 (Hurricane Wilma's landfall in Florida). Image credit: NOAA.

You don't have to be a meteorologist or climate scientist to see that something stood out like a big sore red thumb! I compiled that and a bunch of other charts for that time period, which illustrate the meteorological connection between that anomaly and the extreme explosion of tropical cyclones that season particularly in the eastern Gulf and western Caribbean, and in December 2005 I posted a blog containing that material as a sidebar to a longer entry titled "It's Time to Wake Up and Smell the Thawing Permafrost," in which I described my overall "change from hard-core skeptic to my current way of thinking."

Climate and weather are not two separate entities; they are just different time scales that are intimately and inexorably linked. And in regard to that, per this email I sent to colleagues, things I continued observing pushed me completely over the edge to the dark side!

From: Ostro, Stu
Sent: Monday, December 04, 2006 5:12 PM
Subject: RE: unprecedented december severe weather outbreak in the Northeast Friday

The amount of oddities (not just "extremes") - seems to continue to increase, and many of them can be directly related to stronger and warmer ridges (some transient, some persistent) and/or the feisty troughs that seem to be developing in response.

2006 reinforces to me something which I had decided by the end of 2005, which is that 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.

I know that's sacrilege from the standpoint of what conventional wisdom considers to be the sound science, but ... while one single event indeed does not demonstrate anything ... given the context with all the other things going on, if there had been any remaining reasonable doubt in my mind this severe convective outbreak has helped to further ease it.

The hits just kept on coming, and led me to post a blog in September 2007, "A Connection Between Global Warming and Weather," in which I proposed my hypothesis of what was happening to the atmosphere and its weather as a result of the warming, a key being strong ridges of high pressure aloft, and which I am now endeavoring to adapt to a peer-reviewed paper. Along with that entry I documented cases of individual weather events with apparent connections to climate change, which has become a hobby and grown to a gazillion slides, a compendium of events from those in the 2005 hurricane season to exceptional heat waves to epic floods to unusual snowstorms and topsy-turvy weather patterns to tornado outbreaks unusually far north for the time of year to Superstorm Sandy and its exceedingly unusual track hooking back to the coast.

There have been things which have "tested my faith." And in one sense, it actually is a matter of that, as with most people not being climate scientists, it's a question of whether we have faith in those scientists and their research.

The climate system, though—the atmosphere, land, ocean and sun—is not a religion or conservative or liberal and does not read emails about hiding the decline or whatever and care about spin about global warming having stopped in 1998 or whenever or about human legislation. It obeys the laws of physics, thermodynamics and chemistry.

And while as a meteorologist my perception will always be informed by the fact that there have always been extremes in temperatures and precipitation and storms, having been an operational meteorologist for decades I am convinced beyond a reasonable doubt that their nature is changing, and generally not for the better. There is much research that has been published about this, and each weather event needs to be looked at in context, not in isolation.

Arctic sea ice volume "death spiral." This graph divides each calendar decade into 10 'slices,' one for each year in that decade. The average September Arctic sea ice volume is plotted for each year, moving clockwise around the graph and taking one full decade to complete a circuit. The average volume of sea ice for any particular September is represented by that plot's distance from the center of the graph; as shown by the vertical axis, more ice volume places the plot farther from the center of the graph, while less ice volume places the plot closer to the center. Image credit: Jim Pettit

In January 2009 I posted a blog of a much different kind, about detection of weather and cancer and meteorological and medical similarities involved in the challenge of that. The need to observe, assess and react to threats applies through the climate-weather timescale continuum as well as to human health.

The Earth is not a test tube with which a parallel experiment can be conducted. The difference between what the planet's climate and weather would be without versus with anthropogenically increased greenhouse gases cannot be "proven." And yes, models can be wrong. But that includes seriously under-predicting the rapidity with which the amount of arctic sea ice is declining, and what's happening in places such as the Arctic Ocean and Greenland further convinces me that something ain't right, something that is not business-as-usual and cannot be explained exclusively by natural variability which has always existed, something that is already having profound effects.

The preponderance of multiple lines of evidence is convincing (and dare I say alarming—does that make me an alarmist?), and whether the human body or climate/weather, whether a sharp pain or disappearing summer arctic sea ice or unusually high 200-500 millibar heights, there can be detectable warning signs of a condition with grave consequences.

Oughtn't we to take those signs on our Earth seriously?

Stu Ostro is a Senior Meteorologist and Senior Director of Weather Communications at The Weather Channel. Stu leads the team of weather experts at TWC. A focus of his in recent years has been identifying possible connections between climate change and day-to-day weather, and he has documented many cases as part of an analysis project.
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