I happen to firmly believe that climate change is real, it is happening, and humans are contributing to and largely responsible for it, but don’t worry — this isn’t going to be a political story. And I’ll admit that I can completely understand some of the deniers’ arguments. No, not the ones that say that “global warming” is a hoax made up so that “evil liberals” in government can tax everyone even more. The understandable arguments are the ones that say, “How could mere humans have such a big effect on the world’s climate?” and “Climate change is cyclic and will happen with or without us.”
That second argument is actually true, but it doesn’t change the fact that our industrialization has had a direct and measurable impact in terms of more greenhouse gases emitted and the planet heating up. Also note: Just because you’re freezing your ass off under the polar vortex doesn’t mean that Earth isn’t getting hotter. Heat just means that there’s more energy in the system and with more energy comes more chaos. Hot places will be hotter. Cold places will be colder. Weather in general will become more violent.
As for the first argument, that a single species, like humans, really can’t have all that great an effect on this big, giant planet, I’d like to tell you a story that will demonstrate how wrong that idea is, and it begins nearly 2.5 billion years ago with the Great Oxygenation Event.
Prior to that point in time, the Earth was mostly populated by anaerobic organisms — that is, organisms that do not use oxygen in their metabolism. In fact, oxygen is toxic to them. The oceans were full of bacteria of this variety. The atmosphere at the time was about 30% carbon dioxide and close to 70% nitrogen, with perhaps a hint of methane, but no oxygen at all. Compare this to the atmosphere of Mars today, which is 95% carbon dioxide, 2.7% nitrogen, and less than 2% other gases. Side note: This makes the movie Mars Attacks! very wrong, because a major plot point was that the Martians could only breathe nitrogen, which is currently 78% of our atmosphere but almost absent in theirs. Oops!
But back to those anaerobic days and what changed them: A species of algae called cyanobacteria figured out the trick to photosynthesis — that is, producing energy not from food, but from sunlight and a few neat chemical processes. (Incidentally, this was also the first step on the evolutionary path to eyes.) Basically, these microscopic fauna would take in water and carbon dioxide, use the power of photons to break some bonds, and then unleash the oxygen from both of those elements while using the remaining carbon and hydrogen.
At first, things were okay because oxygen tended to be trapped by organic matter (any carbon containing compound) or iron (this is how rust is made), and there were plenty of both floating around to do the job, so both forms of bacteria got along fine. But there eventually became a point when there were not enough oxygen traps, and so things started to go off the rails. Instead of being safely sequestered, the oxygen started to get out into the atmosphere, with several devastating results.
First, of course, was that this element was toxic to the anaerobic bacteria, and so it started to kill them off big time. They just couldn’t deal with it, so they either died or adapted to a new ecological niche in low-oxygen environments, like the bottom of the sea. Second, though, and more impactful: All of this oxygen wound up taking our whatever atmospheric methane was left and converting it into carbon dioxide. Now the former is a more powerful greenhouse gas, and so was keeping the planet warm. The latter was and still is less effective. The end result of the change was a sudden and very long ice age known as the Huronian glaciation, which lasted for 300 million years — the oldest and longest ice age to date. The result of this was that most of the cyanobacteria died off as well.
So there you have it. A microscopic organism, much smaller than any of us and without any kind of technology or even intelligence to speak of, almost managed to wipe out all life forms on the planet and completely alter the climate for tens of millions of years, and they may have tipped the balance in as little as a million years.
We are much, much bigger than bacteria — about a million times, actually — and so our impact on the world is proportionally larger, even if they vastly outnumbered our current population of around 7.5 billion. But these tiny, mindless organisms managed to wipe out most of the life on Earth at the time and change the climate for far longer than humans have even existed.
Don’t kid yourself by thinking that humanity cannot and is not doing the same thing right now. Whether we’ll manage to turn the planet into Venus or Pluto is still up for debate. Maybe we’ll get a little of both. But to try to hand-wave it away by claiming we really can’t have that much of an impact is the road to perdition. If single-celled organisms could destroy the entire ecosystem, imagine how much worse we can do with our roughly 30 to 40 trillion cells, and then do your best to not contribute to that destruction.