The Hockey Stick

If you’ve been reading this blog since its third post, then two things can be said:

  1. You have some combination of very low standards and not enough to keep you occupied
  2. You know I love sports, and hockey in particular

I’ve tried my hand at both ice and roller hockey. Well, really only once in roller hockey – I got so freakishly overheated in my gear that I haven’t played again since. Ice hockey provides the perfect balance of heated metabolism in a chilled environment. Fire and ice, so to speak.

I didn’t play hockey as a kid. In fact, I never got on ice skates until two weeks before my first game. At the end of 1991, my roommate and I threw a New Year’s Eve bash at our apartment, and my newfound friends from graduate school were among the attendees. As we were standing around the keg, already vigorously hydrated, someone said “hey we’re gonna start an intramural hockey team, you wanna join?” My vigorously hydrated response was “Sure! I’ve never skated before but I’ll play goalie!” (Editor’s note: the goalie is generally supposed to be the most skilled skater on the team). My first game was an affair to remember; I didn’t put my skates on until the end, so I couldn’t tighten them enough, and I was falling off my ankles the entire game. I had to be helped off the ice. But by the end of the season I made a couple of saves and was unanimously voted “most improved player”. Apparently none of the early struggles discouraged me; I still play today (although I’ve mostly hung the goalie pads up).

Around the same time I took up hockey, I was starting my own graduate work with that same group of friends. My degree was Aerospace Engineering Sciences, and my focus area was remote sensing, which is basically trying to gain information about something without touching it. More specifically, I worked in satellite remote sensing, which is trying to gain information about the Earth from an instrument perched in space. Even more specifically, I was working on algorithms that try to infer where and how much it is raining. In order to do that, I needed to take some classes about atmospheric physics, and the University of Colorado was gracious enough to offer them. It was during those years in the early 1990’s that I got to take a longer look at what was then called “global warming”, a name just as unfortunate as “the greenhouse effect”.

A few years earlier, as an undergraduate, I attended a “global warming” themed event at the university, right in the middle of an Arctic blast that had Colorado submerged in below-zero weather for a couple of weeks straight – and of course we all thought that was at least very funny, and at most an indictment of “global warming”. Today, anytime it gets unusually cold anywhere, somebody inevitably says “so this is global warming, huh?” Which is why “global warming” is a very unfortunate term indeed, and has generally been replaced with “climate change”. Equally unfortunate is that the new term hasn’t been able to escape the stigma of the old one.

Here’s one problem with the term “global warming” and the broader concept of generally “hotter temperatures” in recent years: they don’t match up well with day-to-day human experience and perception of temperature. We don’t directly sense a globally averaged temperature; we sense the temperature of where we are, at a given location and a given moment in time. In other words, we directly sense weather, but climate change is not about weather, it’s about, well, climate.

Here’s another problem: what’s really happening with climate change is that more energy is being trapped in the Earth and its atmosphere, and sometimes that means it gets hotter somewhere, and sometimes it means it gets colder somewhere else, and sometimes it translates into specific events, like a more intense storm drawing from the higher amount of available energy. This includes all kinds of storms, including winter storms, which make us all think of exactly the opposite of “warming” and “heat”.

All of that said, a broader effect of our recent changing climate is that the Earth, on average, is getting warmer. So first, how do we know that? The answer is the result of a monumental effort across multiple domains of science, and across a century and counting of time. I could spend pages upon pages going through all of that, and I still wouldn’t do it justice. I also wouldn’t be able to tell you any better than the brightest scientists across the world, who have been studying the topic for decades. So I’m going to start by pointing you at one of their websites, the most recent assessment by the Intergovernmental Panel on Climate Change (IPCC).

Now, if you are one of those folks that simply don’t trust the scientific consensus on this issue, there is nothing I will be able to say to change your mind. I could hope you’d go to their website and see the thoroughness of their work, as well as their own admissions about where they are more or less confident about various aspects of the issue. I could hope you’d then read the references they cite, and then use your favorite search engine to bounce off the counter-arguments, giving all of it an equal and unbiased treatment. But since hope alone doesn’t write blogs, I’m going to continue here as though you did all that, whether you did or not.

So let’s talk more about temperature. The Earth has been around for four and a half billion years, which is long enough to have seen a lot changes in its globally averaged temperature. We can make educated inferences about the climate hundreds of millions of years into the past, based on what the fossil and rock records indicate. We can infer the temperature and concentrations of various atmospheric gases in the polar regions by drilling ice cores, sometimes over two miles deep and extending back to 800 million years. For more recent estimates, we can look at tree rings or even written records. For even more recent estimates, we have actually deployed instruments across the Earth that can measure temperature and concentrations of atmospheric gases. For the most recent estimates, we have had satellites in orbit that can measure these things by collecting the photons that are cascading from our Earth back into space.

Putting all of these things together, and comparing them to one another as best we can so that we know we’re dealing with apples and apples, if you look at a graph of temperature versus time over the past millennium, you get something looking like a hockey stick: a long period of fairly steady or even slightly declining temperature (the shaft) followed by a short period of rapid warming (the blade).

The hockey stick graph has been a subject of vigorous debate since it first came out in 1998. But on the whole, the general idea conveyed by the graph has survived this scrutiny: it is considerably warmer now than it has been in at least the last thousand years. The next question is “why?” Well, let’s take a look at the graphic below, basically “Figure 1” from the report I linked you to above.

Kinda looks like there’s a correlation here, no?

The first graph above (a) is the change in globally averaged temperature (degrees Celsius) since 1850. On the “hockey stick” graphs that go back to the year 1000, the increase shown starting in the early 1900’s gets squished to the right, very good for showing an image of a hockey stick, but not so useful for seeing what happens during the increase, which is why I’m not showing you the hockey stick graph.

A couple of things to notice in (a): first, even globally averaged temperature varies naturally from year to year or even over a period of years. Some of this is just pure chaos, while some of it is due to combinations of events like the solar cycle or the eruption of a volcano here and there. The second thing to notice is the general trend toward warmer temperatures over time. A number of volcanoes have erupted during that time, which tends to block sunlight with ash and have a cooling effect, but there hasn’t been any noticeable trend in volcanic eruptions either way. The solar cycle is eleven years, but the upward trend in temperature has lasted beyond several of those. So the Sun and Earth themselves don’t seem to be the likely causes for the increase in temperature.

Ok, now look at the second graph (b). Sea level is another thing we have progressively become better at measuring over time, and the trend is eerily similar to that for the temperature. That shouldn’t be too surprising: warmer temperatures means more ice melts, putting more liquid water into the oceans. Now look at graph (c). That’s the increase in “greenhouse gases” over the same period of time, including carbon dioxide. Now look at graph (d). That’s the increase in the amount of carbon dioxide from the stuff we do. So, in summary, (a) says the Earth is getting warmer, (b) seems to confirm (a), (c) says it’s likely due to increased greenhouse gases, and (d) says that’s likely our fault.

To state it more scientifically, here are the words of the IPCC:

Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen. 

Anthropogenic greenhouse gas emissions have increased since the pre-industrial era, driven largely by economic and population growth, and are now higher than ever. This has led to atmospheric concentrations of carbon dioxide, methane and nitrous oxide that are unprecedented in at least the last 800,000 years. Their effects, together with those of other anthropogenic drivers, have been detected throughout the climate system and are extremely likely to have been the dominant cause of the observed warming since the mid-20th century.

When a scientist (and especially a large group of scientists) says things like “unprecedented”, “extremely likely”, and “dominant”, people should listen. Given what clearly appears to be happening, the next post will talk about where we think that might lead in the future. But for now, consider perhaps the most tragic consequence of climate change: if it continues to get warmer, all the ice will melt for good, and eventually it will not be cost effective to keep ice frozen in large buildings, and hockey will be eliminated from society, turning the “hockey stick graph” into the omen to end all omens. I for one do not want to live in such a world.

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