|Credit: Arturo de Frias Marques from Wikipedia|
First, let's change the question a bit to make it less argumentative. How about this, "Why should I care if polar bears die?" Let's assume it's an honest question from someone who seriously doesn't care about the polar bear as an amazingly well-adapted mammal that endures an incredibly harsh environment that few humans merely visit once in a while. Effectively 100% of the world's population will never see a real, live polar bear in its natural habitat. We don't eat them. What we eat doesn't eat them. What good are they to us anyway? As I alluded to in my curt response above, the question of the polar bear's existence and subsequent worth is really about general systems thinking. The polar bear isn't an isolated species, but part of a system—multiple systems in fact. Let's look at two of them, starting with the easier system of the two.
The Food Chain
The polar bear is at the top of its local food chain, meaning it doesn't have any natural predators. It primarily eats seals, although it will hunt and consume almost anything that moves in its environment, with varying degrees of success. It's generally quite difficult to bring down an adult walrus or drag a narwhal or beluga whale out onto the ice, but it's been known to happen occasionally. The polar bear's hunting grounds are almost exclusively the frozen ice of the Arctic Circle from fall to spring. They need the ice for their hunting methods of lying in wait at seal's breathing holes or sneaking up on unsuspecting prey, aided by their white coats camouflaged against the white ice and snow of their surroundings. They are ineffective hunters in the water, and most prey can easily outrun them on the arctic tundra.
Polar bears will also scavenge for food and will eat animal carcasses when they find them. They're not picky eaters by any stretch of the imagination. You can't be if you live on a giant floating block of ice. You eat what you can or starve to death instead. So what happens if the polar bear does die off? Most likely, the seal population will grow because more of them will live longer and reproduce more. That means their food source, mostly fish, will shrink as more seals are eating more fish. Seals have other predators, including killer whales and sharks, and the populations of those predators may increase to compensate for the increased seal population. The food chain effects of losing the polar bear will continue to ripple out from there, with the changing populations of seals, fish, killer whales, and sharks affecting a larger and larger circle of animals, and plants as well.
Then there's the dead animal carcasses. There's going to be more of them without the polar bears around to clean them up. Scavengers play an important role in the ecosystem, preventing the spread of disease by consuming carcasses before they rot and breed bacteria and other pests. It's possible that other animals would fill the gap that polar bears would leave behind as the Arctic Circle's garbage disposals, but the risk is that no polar bears means more rotting carcasses on any ice that still forms in the winter, especially because the seal's primary predator has gone missing. They may change their behavior to spend more time on the ice away from their other predators in the water, and that would only increase the number of seals that perish on the ice, simply from old age.
The system will almost certainly reach a new equilibrium, but it's hard to predict what lasting effects it would have, and whether we would want the results or not. Once the polar bear goes extinct, it's too late to go back and choose the other option. This may not be a convincing reason to be concerned about polar bears. I can see how a re-adjusting food chain in the Arctic Circle is not something the average person will get worked up about. It doesn't affect most people directly, just like most people won't miss seeing a live polar bear if they go extinct. That's fair, I guess, but the other system we're going to talk about is different. It's going to affect a lot of people directly. I would say nearly everyone.
The Earth's Climate System
The polar bear depends on the Arctic ice as its hunting grounds. It needs plenty of ice for most of the year—save a few months in the summer—to be able to eat enough seals to last through the low-ice season when it can't really hunt. The reason that the polar bear is threatened now, even with its population increasing or stable in the last couple decades, is purely because of the existential loss of its habitat from melting Arctic Sea ice. The habitat of the polar bear is literally disappearing.
|Credit: Michael de Podesta from Protons for Breakfast|
What I like about the question, "Why should I care if polar bears die?" is that it has an implicit admission that climate change is real. If the Earth wasn't heating up, causing the Arctic Sea ice to melt more and more each year, the polar bear wouldn't be threatened at all. The hunting regulations in place seem to be doing their job, and the polar bear population is otherwise healthy. The whole reason to ask such a question is because of a possible future where there is not enough ice to support polar bears in the Arctic, causing them to go extinct. That future would only happen if the Arctic was warming up, resulting in an acceleration of melting ice, and the reason it's warming up is because we're pumping too many greenhouse gases, namely CO2, into the atmosphere.
On the surface we seem to be in agreement on that, otherwise he wouldn't have asked a question about polar bears dying. Maybe. If you want to learn more about why CO2 is such a problem for the planet at high concentrations, this four-part series is the best technical explanation I've seen yet for how CO2 causes increased global temperatures.
This is where things get serious because this whole question about whether or not to save polar bears is not really about polar bears. Polar bear extinction is only one symptom of a far-reaching cause within a huge, complex system. That cause is climate change, and the system involved is the Earth's climate system. It's massively complex, and the polar bear is one species that's on the forefront of the changes that are coming. They're our canary in the coal mine, except this time the coal mine is Earth, and we don't have anywhere to escape to if the canary dies.
We took a big leap from polar bear extinction due to melting Arctic Sea ice to catastrophic climate change, so let's see why melting ice is such a bad sign. It's not because melting Arctic Sea ice causes the ocean levels to rise. That doesn't happen because the ice is already floating in the Arctic Sea, already displacing all of the water that it would otherwise turn into when it melts. To see this for yourself, you can take a glass measuring cup, fill it halfway with water, and add some ice cubes (the bigger the better). The addition of ice increases the level of the water because it's been displaced, but also notice that the floating ice cubes are partially raised above the water. Take note of the water level now before waiting for the ice cubes to melt. Once they are fully melted, you can see that the water level has remained the same as it was just after you added the ice cubes. The Arctic Sea ice will behave exactly the same way.
Then why should we be worried about the Arctic Sea ice melting? For one thing, that's not the only massive deposit of long-lived ice we have on Earth. There's a total of about 29.5 million km3 of ice on the Earth in the form of glaciers and ice sheets, and the Arctic ice only accounts for about 5,000-20,000 km3 of that (it varies a lot from summer to winter). A much larger portion is contained in the Greenland ice sheet at about 2.6 million km3, but the vast majority of the world's ice is in Antarctica, with a whopping 26.5 million km3 or about 90% of the world's ice.
|Credit: Dave Pape from Wikipedia|
The next thing to consider is that there is not likely to be a scenario where the Arctic Sea ice completely melts, but none of the Greenland or Antarctic ice sheets melt. In fact, some of the giant ice shelves of Antarctica have already broken apart, and it is believed that once these shelves break away, the glaciers behind them will more quickly stream into the ocean. In addition to that, it has been known for quite some time that the temperature at the poles increases at about twice the rate that the average global temperature does because of heat transfer within the global climate system.
As these ice sheets melt, the sea level will rise, and if all of the ice melts, there could be about a 65 m rise in sea levels. That's an incredible change that would reshape the worlds coast land. You can see what such a change in sea levels would look like at National Geographic. Of course, this change wouldn't happen all at once, and all of the ice would not melt for many lifetimes, even on an accelerated warming path. But, the sea level doesn't need to rise by 65 m to cause an awful lot of damage, pain, and suffering, and the climate system has tons of inertia to it. It's going to take a large concerted effort to turn it around, so once sea levels start rising significantly, they'll continue to do so for quite some time.
|Credit: National Geographic|
Keep in mind that most of the world's largest cities are on the coasts. Financial centers like New York and London, technology centers like San Francisco, and manufacturing hubs all over East Asia would all be at risk of catastrophic flooding even with a 5 m rise in sea levels because of how low-lying they are. As the world's oceans get warmer, storms get stronger, and the coasts will get hit with more and more damaging storms. If the major areas of finance, technology, and manufacturing that support our modern civilization are constantly under threat of rising sea levels and flooding, what will that do to the world economy, let alone all of the lives directly in harms way? The Earth's climate system is a complex, interconnected system where polar bears are only a small component in a huge network of interconnecting pieces. Understanding that system and what it means when parts of it behave in certain ways or how different parts respond to changes in inputs is becoming critical to the continued progress and success of our civilization.
Let's review this series of links again. If polar bears, our canaries in the coal mine that is Earth, go extinct, it will be because they lost their habitat. The Arctic Sea ice will have melted, and that would happen because of rising temperatures at the poles. That would mean the Greenland and Antarctic ice sheets are also at risk of significant melting, and a complete melting would cause a 65 m rise in sea levels along with much stronger storms and catastrophic flooding to coastal areas. Much of the world's financial districts, technology development, and manufacturing are in coastal areas, and are at risk of tremendous disruption and damage. So yeah, I do care if polar bears die, and it's not just because I care directly about polar bears. It's because I care about the future of humanity and our civilization, and if the polar bears go, we better really start thinking hard about how we're going to survive in this mine we call home.