Warmer global temperatures will obviously lead to the melting of more ice, which will remain in the form of liquid water. Thus, polar ice caps will shrink, and glaciers will disappear. Do we have evidence that this has occurred? If you’ve watched the movie or read the book An Inconvenient Truth by Al Gore, then you’ve seen a number of dramatic examples of these sorts of changes. Indeed, they’re quite startling because many of these changes have been observed within the span of one human lifetime, unlike most of the extremely gradual changes that our planet has gone through in its 4.5 billion–year history.
Looking at satellite photos of the Arctic polar ice cap taken over the last thirty years, it’s easy to note a dramatic change in its size in a time span of less than one generation. The Arctic and Antarctic regions are the most sensitive areas on Earth to changes in global temperature, in part because the difference in temperature between water in ice form and liquid form is relatively small.
Some people acknowledge that global warming is a reality but try to argue that it isn’t causing a climate crisis at all; they point out the potential benefits from some of the effects of a warmer global temperature, such as warmer winters in the more moderate latitudes. Another potential benefit often mentioned is that a decrease in Arctic ice would provide a better northwest passage that could be used for global transportation, making it easier for ships to travel from one side of the planet to the other by using a route north of Canada.
Indeed, these may well be isolated benefits that might occur as the observed trends continue. However, there are many more disadvantages to global warming than there are benefits. In fact, the loss of ice on our planet means there will be less sunlight reflected back into space. White snow and ice, such as that on Earth’s poles and glaciers, is much more reflective than the blue ocean or most of the land masses. This reflective property is referred to as albedo; the higher the albedo, the more reflective the planet’s surface is.
As Earth loses some of its ice to global warming, the planet’s albedo will decrease. More sunlight will be absorbed rather than reflected back into space, and this will lead to greater amounts of infrared radiation produced. The heat that results will of course remain trapped within the insulating effects of the greenhouse gases in our atmosphere and contribute to even greater temperature increases. The entire process has the very real possibility of becoming a runaway reaction, feeding into itself with a never-ending cycle of increasing temperatures, melting ice, decreasing albedo, increased absorption of sunlight, increased infrared radiation, increased global temperatures, and so on. I think the devastating effects that could result from this process far outweigh the benefit of easier sea travel through the Arctic or a milder winter in Canada. (And I don’t believe I’m the only one who thinks this way.)
Obviously, polar ice caps aren’t the only source of ice on our planet that can melt. Another loss of ice from global warming is the retreat of the planet’s many glaciers. Many dramatic examples are available to demonstrate this, but I’ll mention only one because the point doesn’t need any greater emphasis in my opinion than that. (Many glaciers are retreating, however, and you would be hard-pressed to find one that has been expanding in size in recent years.) The Grinnell Glacier is located in Glacier National Park in Montana. Photographs taken over the years from the 1930s to the present day have shown an obvious retreat in its size, with very dramatic changes that have been easily observed in such a short time. Glaciologists predict that there will be no glaciers remaining in the park after 2030 based on the current trends in global warming that have been observed. When that happens, it seems likely that this once-beautiful natural wonder and the national park where it’s located will both need a name change. (Admittedly, such name changes would be the least of the problems associated with melting glaciers.)
With all this ice melting, the added water has to go somewhere; what impact it has will depend on where the ice was located in the first place. For example, Arctic ice is floating freely in the ocean like a giant ice cube because, unlike the Antarctic, there isn’t a land mass at the North Pole. When ice at the North Pole melts, it becomes liquid water. What may not be immediately obvious, however, is that water levels in the ocean won’t rise as a result of this ice melting. When floating ice melts, the water level doesn’t change. As the polar ice cap melts, it adds its mass in water to the ocean, equal to the amount it was displacing earlier while it was essentially a floating ice cube, so the sea level doesn’t rise.
Then where does all of the concern over rising sea levels come from? The problem is that Arctic ice isn’t the only ice on our planet that’s melting. There’s plenty of ice on land masses such as Antarctica and Greenland, with large ice shelves hanging over the water, some more than a kilometre thick. There are also a number of glaciers all over our planet. Since these sources of ice are on land rather than floating, they aren’t displacing any water, a situation that’s different from the ice in the Arctic. As glaciers melt, or as large masses of ice break off from ice shelves and make their way into the ocean, they are indeed adding to the global pool of water, making the water levels rise. Land ice melting will lead to a rise in sea level. It doesn’t matter whether the addition takes the form of ice (before melting) or water (after melting). It still leads to a rise in sea levels.
These processes generally do make our ocean levels rise, and that fact has been verified. According to Australia’s national science agency (the Commonwealth Scientific and Industrial Research Organisation, or CSIRO), the current rate of rise for ocean levels is close to 3.0 millimetres, or a little more than a tenth of an inch, a year, proven by careful observations using satellite technology. Earlier in the century, it was closer to about 1.8 millimetres, or 0.07 inches, per year. Therefore, the rate of rise is actually increasing, as one might expect given the trends of increasing greenhouse gas emissions and the rising global temperatures associated with them. In addition to the added pool of water from melting ice, part of the rise in ocean levels is also due to expansion of the ocean itself, resulting directly from the increase in temperature because warmer water is less dense than colder water. In one century, that could mean an increase of twenty-six centimetres or ten inches if this rate of rise remains constant, and even more if the rate continues accelerating exponentially, as it has been.
As ocean levels rise, water levels will increase along the world’s shores, leading to coastal flooding. Coastal flooding will have major consequences because much of Earth’s population is located near sea level. About two-thirds of the planet’s cities with a population greater than 5 million people are vulnerable to a rise in sea level. In China, for example, 11 percent of the population (144 million people) will be adversely affected by the rise in sea levels predicted for the next century. The change is slow, unlike a tsunami or hurricane with the rapid flooding associated with those disasters, but it will still have a significant impact on the many millions of people who will be living there.
Another consequence of greater levels of greenhouse gases, including carbon dioxide, in the atmosphere will be greater amounts of carbon dioxide absorbed into our oceans. Some skeptics consider this to be one of Earth’s natural compensatory mechanisms to deal with the problem so that we don’t have to, but it’s not as simple as that. Since carbon dioxide is a gas, it can easily become absorbed into water just like oxygen can. (Otherwise, fish wouldn’t do too well—they need oxygen just like we do, and they filter oxygen in the water through their gills.) Once absorbed into water, carbon dioxide can form carbonic acid, commonly found in carbonated beverages.
CO2 + H2O ⇔ H2CO3
Since the back-and-forth arrow separating the two sides of the equation is present, this is an equation showing equilibrium. That means that if everything is in a closed system with nothing added or removed, then the amounts of the carbon dioxide, water, and carbonic acid will remain constant for a given temperature. Adding more carbon dioxide, however, will drive the equation to the right, producing more carbonic acid; conversely, if carbon dioxide has a chance to escape and vent away, then the equation will be driven more to the left, like a carbonated beverage going flat.
Thus, more carbon dioxide being added to the atmosphere means more is absorbed into our oceans, producing more carbonic acid in the process. This will lower the pH in our oceans. The pH is a measure of how acidic something is. (The term pH likely refers to the “power of hydrogen,” although there is some debate as to how the term truly originated.) Something neutral, such as distilled water, has a pH of 7. Anything with a pH less than 7 is acidic, and anything with pH greater than 7 is basic. (Basicity is the opposite of acidity, just as a base is the opposite of an acid. When an acid and a base combine in chemical reactions, they produce a salt and water. It always comes back to some chemistry, doesn’t it?)
The mathematics involved are too complicated to review here, but it’s worth knowing that the pH scale is logarithmic, which means every number lower on the scale indicates that a substance is ten times more acidic. As an example, orange juice which contains citric acid has a pH of around 3, and the acid in your stomach known as hydrochloric acid is closer to 1. Since gastric acid is two lower than orange juice on the pH scale, stomach acid is about 100 times more acidic because it is two factors of 10 away, and 10 × 10 = 100. In the other direction, bases include baking soda, which has a pH of around 9, and bleach has a pH of about 13.
The pH of our oceans is about 8.2 at present, but with the amount of carbon dioxide being added and more carbonic acid being produced as a result, the National Oceanic and Atmospheric Administration in the United States projects that the pH in our oceans will fall to around 7.8 by the beginning of the twenty-second century. That may not seem like much, but since it’s on a logarithmic scale, it’s a lot more of a change than it appears. It means our oceans will have increased their acidity by about 150 percent since the start of the Industrial Revolution.
The impacts of such a change in ocean chemistry can be devastating. Species that build shells, such as crabs and lobsters, won’t thrive very well because the calcium carbonate incorporated into their shells will have a greater tendency to dissolve in such an acidic environment, threatening these species with extinction. Coral is another sea-dwelling organism that requires calcium carbonate to exist, so a more acidic ocean will slowly dissolve our coral reefs as well. This not only threatens the coral directly but also threatens the many species that cohabit with them in their complex ecosystems, including more than four thousand species of fish along with many mollusks and crustaceans, all of which use coral as places to live and breed. Corals contribute important medical benefits to our species as well; they provide compounds that have been used in medicines for cancer and HIV/AIDS and have also been used in bone grafting for humans. A more acidic ocean also will likely interfere with the healthy maturation of some fish larvae, possibly threatening them with extinction.
In other words, this small change in the ocean’s pH may have consequences to our planet that are almost too difficult to imagine, but given how much we rely on the animals in the ocean for food, we may be dooming ourselves to negative health and economic effects if we allow these trends to continue.