At first glance, you may have thought that title addresses the obvious: of course climate change matters. We hear about the science and consequences quite often, unless you rely on right-wing sources for your news. Scientists overwhelmingly agree that climate change is happening, that it is caused by human activities, and that it is having and will have increasingly large impacts on society and our planet in the future. But allow me to take the opportunity to put these big ideas into a more digestible form and link the natural science more explicitly to economics in two parts. I’ll do this with the caveat that I am an economist and not a climate scientist, so my science explanations in this part will not be quite as detailed. The next post will focus more on economic theory and its links to what I describe here. First, I have watched presentations of climate research that have been utterly derailed by an audience member asking how we can be sure that anthropogenic (that is, human-caused) global warming is happening. Simply put, we have several sources of evidence that gives the scientific community its high level of confidence. Let’s start with some theories and pieces of information that we know. Scientists have long understood that different combinations of gases, such as the mix that is found in our atmosphere, absorbs and emits radiation from the sun at different rates. At the atomic level, greenhouse gases like carbon dioxide are more likely to absorb and then re-emit infrared radiation from the sun. Nitrogen and oxygen, the other big atmospheric components, do not absorb infrared radiation. To think about how this affects things on a planetary scale, imagine that the earth is a big pot of water that is being heated on a stovetop (the sun) and has achieved an equilibrium temperature. Uncovered, a lot of the heat from the pot just escapes into the room (space), but covering the pot with a lid keeps more of the heat trapped and makes the water even hotter than it would be otherwise. When more greenhouse gases are emitted, it is as though we are putting an ever-thicker lid on our metaphorical pot. All of this theory seems to make intuitive sense, but is it backed up empirically? YES! These observations come from a number of sources on the land, in the water, and from satellites collecting data from space. NASA has a great summary of such observations. The conclusion is that the world is warming consistently and the concentrations of greenhouse gases are rising. We know from industrial records and other sources what humans are emitting, so we can match that with atmospheric observations to precisely understand how the atmosphere is changing. Additionally, scientists have painstakingly researched historical climate conditions in a variety of ways to assemble a long record of climate and atmospheric conditions on the earth. For example, samples of bubbles from extracted ice cores preserve the atmosphere at that period in history, allowing them to see the composition of the atmosphere millions of years ago. If that weren’t enough, we also have another planet to observe. Venus is the hottest planet in the solar system because of a runaway greenhouse gas effect. What becomes disturbingly clear from the look at the historical record is that we are entering a climatic period warmer than any experienced by human civilization. Note from the chart below, taken from Vox, that agriculture developed only after the climate had been unusually stable for a long time – this is the conclusion reached by researchers at CalTech from whose data this comes. We also know from our observations that concentrations of carbon dioxide (the most prevalent greenhouse gas) in the atmosphere have increased from about 280 parts per million (ppm) before the industrial revolution to just over 400 ppm now. As a result, the world is about 1 degree Celsius warmer than before the industrial revolution, and, because it takes a while for greenhouse gases to get high enough in the atmosphere to cause warming, the world is certainly locked in for warming close to 2 degrees. The impacts from this you have probably heard of: more floods, more droughts, sea level rise, etc. There are two final things to keep in mind when thinking about all of this. The first is that the damage from global warming maybe exponential and not linear and, for the most part attempts to estimate damage functions are educated guesses. If the “true” damage function is actually exponential, that means that if warming doubles from 1 to 2 degrees, it increases by something like 4 fold rather than doubling. Depending on policy, the world will likely warm by anywhere from 3 to 10 degrees by the end of the century. On the upper end of that scale, the damage becomes truly civilization-threatening – and I do not intend that to be a hyperbolic statement. Even 4 degrees of warming would be incredibly disruptive. The other danger is that things could very well spiral out of control because of feedback loops in the climate system. For example, the permafrost that rings the arctic, mostly in Russia and Canada, contains huge amounts of frozen organic matter. If this thaws on a large scale, that matter will decompose and emit methane. If this happens on a large enough scale, those methane emissions could be enough to trigger more warming and more thawing and more emissions. One feedback loop could then trigger others, such as the collapse of ice sheets that would trigger a cycle as the albedo of the earth would be reduced. Because of the complexity of the global climate system and its inherently chaotic nature, it is very difficult to know just how much warming the world can take before it gets out of control. Recent evidence suggests we are closer to at least the methane feedback loop than we had previously thought. Future posts will discuss the many implications of all of this, but I will say that instead of simply sounding apocalyptic, it should be read as a call for a conservative approach to emissions control – and here I use conservative to mean that we should err on the side of caution because the risks on either side of a climate goal are asymmetric. The issue of climate change shouldn’t be thought of as win-or-lose, that we either escape it or we don’t. There will certainly be some damaging warming. Our goal should be to limit that, and especially to avoid any dangerous feedback loops that could send things spiraling terribly out of control.
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AuthorEconomist. Professor. Environmentalist. Archives
July 2017
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