he global warming debate has raged for decades, and this much, at least, is not in dispute: 1) That human beings have injected hundreds of billions of tons of carbon dioxide and other greenhouse gases into the atmosphere since the start of the Industrial Revolution. 2) That greenhouse gases tend to trap heat in the atmosphere and therefore increase its temperature. 3) That the Earth has grown warmer since the start of the Industrial Revolution, by about one degree Celcius. Figure 1 shows this trend clearly. Furthermore, the temperature is expected to increase by another one to five degrees by the year 2050, depending on which experts you ask. Pretty alarming news--are we baking our planet to death?
Figure 1
Figure 1 is what scientists refer to as a "gee-whiz" graph--one whose scale and axes were chosen specifically to showcase a particular trend. This is fine if you need to isolate that trend for special study, but it can be very misleading if you’re looking for the context and perspective to make real sense out of it. Figure 2, with somewhat broader margins, shows this latest trend to be part of a larger pattern--variations of plus or minus one degree have actually occurred pretty frequently since the end of the last ice age, including one 3,000-year heating period which predates any large-scale human industrial activity. Figure 3 shows much larger excursions--both positive and negative--taking place within the span of human evolution. So as we step back, the "smoking gun" of human-caused global warming becomes a lot harder to distinguish.
Figure 2
Baking, dry and lifeless
The debate, of course, rages on: Are we contributing to the overall heating? Almost certainly. Would reduced emissions on our part help slow the rise of global temperatures? Few reputable scientists would dispute it, although the physics and chemistry of earth-ocean-atmosphere interaction are complex enough to leave some small room for doubt. Still, the controversial Kyoto accord, in which First World nations agreed to reduce their greenhouse emissions by an average of 5.2 percent of 1990 levels, is expected to make a difference of only about a tenth of a degree by 2050, even if we adhere to it perfectly. So with a lot of bickering and effort, we can slow down global warming, but only a little.
Anyway, the question of whether we should slow it down is rarely asked. The presumed default answer--YES!--is based on three assumptions: 1) That warming is bad for human beings. 2) That warming is bad for the environment. 3) That warming could easily lead to a runaway greenhouse effect similar to what we observe on the planet Venus, which might be Earth's twin if it weren't baking, dry and lifeless, at a withering 450ºC. So with tongues firmly in cheek, let's address each assumption in turn, and then revisit the original question.
The global Hawaii effect
The idea that global warming is bad for humans seems pretty darned obvious at first blush. After all, we evolved during an ice age, and learned to rely on crops which are highly sensitive to climate fluctuations. Furthermore, human history has seen the world's deserts grow dramatically in size, due at least in part to mistreatment on the part of humans living there. Finally, and perhaps most significantly, by nature we are a shore-dwelling species, with 70 percent of our population living within 50 kilometers of the ocean. If global warming were to trigger widespread melting of glaciers and polar caps, rising sea levels would put a lot of our favorite places underwater, which is clearly Not Good. On the other hand, nearly a third of the Earth's land surfaces--the arctic and antarctic regions--are presently uninhabitable by us, and it isn't difficult to imagine what we could do with those lands if they were warm enough to grow wheat, or even pine trees.
Figure 3
Significantly, the Earth's climatic history suggests that global warming affects nighttime temperatures far more than daytime temperatures, winter temperatures far more than summer temperatures, and polar temperatures far more than equatorial ones. Warming is also associated, on average, with increased humidity in the atmosphere. In short, there's a sort of global Hawaii effect, with smaller deserts, longer growing seasons, and less extreme seasonal and geographic variations in climate. The transition from our present climate to that one would certainly be unpleasant, but in the end we might find not only more land but better land available to us on a warmer Earth.
The idea that global warming is bad for the environment is just plain silly, as a quick glance at Figure 4 will show. Except for a handful of cool periods, the Earth has been significantly warmer for most of its history than it is today. During the time of the dinosaurs, for example, the Earth had no ice caps at all, and its polar oceans enjoyed temperatures upwards of 15 degrees Celsius even in the dark depths of winter. There is no evidence that plant or animal growth was harmed in any way by these temperatures. In fact, best evidence indicates that the Earth was teeming with life, even in what today is Antarctica. Some would argue that the real harm to Earthly life came 2 million years ago, when a prison of ice froze and crushed and extinctified every antarctic species unable to swim or fly away.
Figure 4
In addition to its effects on land, global warming has the effect of enlarging the ocean, decreasing its salinity, and increasing the number of hurricanes, which mix the waters and prevent the sort of stagnation and oxygen depletion which so trouble our fisheries today. And if some human cities are drowned, they should at least provide excellent and all-but-unfishable habitats for the sea creatures we've hunted so ruthlessly. Where's the deep-ecological problem with that?
The catastrophic edge
The last and most troubling assumption, the idea that the Earth could slide into a runaway greenhouse effect and wind up looking like its sister world Venus, is impossible to dispute. Dump enough heat and CO2 into the atmosphere and this will happen, definitely, without a doubt. And, alarmingly, our sea floor and polar caps include deposits of methane-rich ice called clathrates which, if disturbed by heating or flooding or hurricanes, could release even more greenhouse gases into our atmosphere. However, the atmosphere is where many of these gases came from in the first place, and we do know from our fossil record that temperatures as much as eight degrees Celsius above our own have occurred before, without permanent consequence. There certainly is a catastrophic edge out there somewhere, and we don't want to fall off, but at least we know we're nowhere near it. A runaway icehouse effect is 100 percent possible, too, and we know that's at least eight degrees away on the other side. In fact, many scientists have speculated that the Earth and its biosphere have evolved active climate control mechanisms to help steer us away from these cliffs. Whether that's true or not, there's no real safety basis for preferring a cooler planet over a warmer one.
Let's face it: climate stability is an unreasonable expectation on any time scale, be it months, centuries, or gigayears. The Earth's temperature will either go up or down; it will never remain constant. So the choice is not "bake to death or don't bake to death," or even "bake to death or freeze to death." We're pretty close right now to the Earth's geologic average temperature, giving us plenty of room to swing either way. The choice is really between a warmer, wetter Earth with less seasonal and geographic variation in its climate, or a colder, dryer, more extreme Earth, possibly headed for a new ice age. I think it's a foregone conclusion that we're helping the Earth to heat up, but maybe the time has come to ask ourselves: are we helping enough?
Wil McCarthy is a rocket guidance engineer, robot designer, science fiction
author and occasional aquanaut. He has contributed to three interplanetary
spacecraft, five communication and weather satellites, a line of
landmine-clearing robots, and some other "really cool stuff" he can't tell
us about. His short fiction has graced the pages of Analog,
Asimov's, SF Age and other major publications, and his
novel-length works include Aggressor Six, the New York Times Notable
Bloom, and upcoming The Collapsium.
