A rate is a simple enough concept; it measures change. If I’m driving my car, my miles per hour are the rate I am covering ground, if I slow down or speed up that brings in a second rate, the rate at which my speed is increasing or decreasing. As a scientist, I think a lot about rates. How fast my bacteria grow, how fast their genes can change, how quickly they can get from one place to another. In fact, a lot of science is based about measuring the rates of things and how they change, it tells us a lot about the natural world. This brings me to climate change. This picture is of a piece of wood. It’s clearly well dried out. It feels light to the touch, still has some bendability to it, but how old it is? Turns out this piece of wood is from the Pliocene (Ply-o-scene) era, making it somewhere around 3 million years old! This came from a tree that was once part of an evergreen forest on the North Slope of Alaska, I picked it out of a bank of thawing permafrost a couple of summers ago. Because it was constantly frozen for 3 million years it still looks much the same now as it did then. As this other picture shows there are no trees on the tundra now, and there haven’t been for a long time. It turns out in the Pliocene, temperatures in the Arctic were enough warmer that spruce forests could grow. It is also estimated that the amount of carbon dioxide (CO2) in the atmosphere during the Pliocene was somewhere around where it is today, 400 ppm. This amount of atmospheric CO2 would have resulted in a warmer Earth, one result would be evergreen forests on the North Slope. Why aren’t they there now? Hint, the rates the thing.
There have been plenty of other changes in the atmospheric CO2 concentration on Earth over the eons. For example during the period known at the ‘PETM’ (I forget what it stands for, but I think it’s safe to Google) approximately 50 million years ago, the estimated CO2 levels exceeded 600 ppm. The point is that the history of CO2 levels on Earth have shown a lot of variation in the past, so what’s the big concern with the fact CO2 levels are getting high again now?
Well there’s a bunch of reasons, but to me, the rate’s the thing. We don’t exactly know the how or the why of carbon dioxide levels reaching 400 ppm in the Pliocene, or >600 ppm in the PETM. There’s a bunch of theories, but none of them involve any evidence for some earlier fossil-fuel burning civilization, instead they are based on changes in geological processes that occur over thousands of years. These time scales are gradual enough that most living systems can adapt to the change, like spruce trees moving into the tundra. The pace at which CO2 is being added to the atmosphere today is generally thought to be at least ten times as fast as during the Pliocene or the PETM. So does that mean the changes associated with a warming planet: increasing temperatures, shorter winters, sea-level rise, changes in rainfall, and storm patterns will also occur ten times as fast? This is so far outside the more normal rates of geological change that’s it raises real concerns about our ability to adapt rapidly enough, not to mention the millions of other species we share the planet with in its many interconnected ecosystems.
So here’s a little thought experiment that has to do with driving and rates of change. Lets say you commute each day between Augusta and Waterville, a distance of 20 miles along a pretty straight, relatively flat stretch of the 4 lane I-95 interstate. Now we’re going to equate the amount of CO2 in the atmosphere to the speed you drive, and make a couple of rules. Cars and trucks are capable of going whatever speed is required, and everyone is driving around the same speed. We’ll start with a CO2 level of 300 ppm (a little higher than pre-industrial levels) and equate that to 75 mph, since most people are cruising a few miles above the speed limit. Then we increase the amount of CO2 to 600 ppm, which is where we’re currently headed, so that equals 150 mph. So, lets say the rate of increase in the PETM was like increasing your speed by 2 mph per year, so it would take 40 years to go from 75 to 150 mph. Forty years is a reasonable amount of time for technology to develop and advance. Suppose you bought a new car every 10 years. To adapt to increasing highway speeds, it’s reasonable to assume each new car would have better power, suspension, braking, and handling, not to mention more impressive self-driving capabilities so that going along at 150 mph in 40 years would be pretty safe. It wouldn’t be quite as safe as going 75; the accident rate might go up by 5%, and the death rate by 2%, since the newer cars would be designed to crash at 150 mph. Your insurance premiums would increase marginally.
So now lets run this scenario at the current rate of CO2 build-up in the atmosphere, which is at least ten times faster than was estimated for the changes that occurred in the PETM. Now you, and everybody else on the road have gone from 75 mph to 150 mph in four years in 20 mph increments. Chances are you’re driving the same car, or maybe one model newer, so not much improvement in handling, braking, power, and only minimal self-driving capability. Now the crash rate has gone up to 50% and the death rate to 85%, because your current car is not designed for you to walk away from an accident at 150 mph. If you do the math of doing your daily commute under these conditions for very long, your chances of survival start to approach zero. Insurance? Forget about it.
This is a very simplified thought experiment about a problem of planetary complexity. The true effects on our planetary ecosystem of our current rate of adding CO2 to the atmosphere, and resulting warming of the planet are far more difficult to predict. Chances are some changes will be less than we can predict, but others will probably be worse. It’s even fair to ask if together these rapid changes are enough to doom civilization. Clearly Homo sapiens have proven to be adept at adaptation, way more so than most of the other species we share the planet with. I wouldn’t bet against us. Still, if we end up trying to drive civilization down the road at 150 mph, in a vehicle designed for 75 mph, it’s going to be a heck of a wreck. Best to take our foot off the gas.