The evidence for this scenario is clear and conclusive, backed up by multiple studies and seen across the world. The unique birds of New Zealand were doing just fine until 800 years ago, when the first Maori arrived and promptly proceeded to wipe nearly all of the flightless and many of the flighted species out. When the Europeans arrived several centuries later, they merely finished the job. The megafauna of South America, once the most biodiverse in the world, died out within centuries of humans arriving, after having endured millions of years of ecological and climatic upheavals with little to no effect. The giant lemurs and fossas of Madagascar were eradicated shortly after the arrival of the first humans 3000 years ago, and the few and tiny populations of elephant birds that had managed to cling on disappeared once again after the coming of the Europeans. Arguably most famous of all recent extinctions is that of the dodo, though what fewer people know is that the dodo shared its island home of Mauritius with a wide variety of odd and endemic species, including giant turtles and multiple other species of flightless birds, all of which were wiped out shortly after people came.
This does not seem like a complicated issue - quite the opposite in fact. Every time humans arrive on a new landmass, the result has been an immediate wave of extinctions. This is seen across the whole world, and evidence for it is ample. Surely, nobody would be naive or stubborn enough to contest this, right? As we will soon see, the bounds of human incredulity and denial are truly limitless.
Raphus cucullatus, the famous dodo. Once abundant across its habitat, it is now, as the saying goes, "dead as a dodo"
It is a well known and undeniable fact that the Earth's climate has changed dramatically over the last ten thousand years or so. The end of the ice age resulted in drastic increases in temperature, along with sea level, humidity, precipitation, and pretty much all other natural processes. It is not then surprising that, upon initially discovering that most of the now extinct megafauna died out around the time of these changes, people presumed there to be a connection. It seems so neat, so convenient, a nice and tidy explanation to satisfy scientists and the crowd alike. Even today, it seems completely logical at first glance: Temperatures are cold, mammoths and other polar animals do well - temperatures get hot, mammoths and other polar animals die out. Even for the non-polar animals, such as the lions and ground sloths, the notion that a rapid change in climate was simply too much for them to adapt to is easy to swallow. Thus, for many years, this was the preferred explanation behind the extinction of the past megafauna, and it seemed to make perfect sense. Over time however, the cracks started showing. First and foremost, improved dating methods started revealing that the timing didn't quite match up. The extinction of the Australian megafauna has typically been associated with a spike in aridity, but recent research has shown that this change occurred shortly after the extinctions, thus ruling it out as an explanation. In Europe, the extinctions are divided into two waves - an initial one 50,000 years ago, and another 10,000 years ago. The first wave, in which the european elephants, hippopotamus, and several other large species went extinction, does not appear to coincide with any major change in climate, and the second wave of extinctions don't seem to be confined to any one point in time. Some species, such as the mammoths, die shortly after the peak of the change, others, such as the cave bears, die out before, and yet others again, such as the tarpans and aurochs, suffer local extinctions, but don't actually die out completely until much later. Animals such as the lions are even more odd, dying out around 10,000 years ago, but then suddenly appearing again around 6,000 years ago.
This is particularly odd if climate change is accepted as the explanation, since the extinctions in North America, similar both in climate and ecology to Europe, occurred pretty much all at the same time, around 11,000 years ago. The inconsistencies continue, as South America undergoes a major extinction event, wiping out nearly all of its megafauna, while Africa, again quite similar in climate and ecology, is virtually untouched. New Zealand, where fossil evidence suggest that multiple species of especially the moa experienced severe range contractions after the end of the ice age, nonetheless doesn't undergo a single extinction until long after the end of the massive changes. When taken as a whole, it starts to become apparent that something is very wrong with the climate change explanation. This is not the end of the problems with it however, as there is one final factor that most people ignore, yet which singlehandedly pretty much renders all of the evidence i just provided unnecessary, as it utterly invalidates the climate change hypothesis: The event we tend to refer to as "The Ice Age", is not actually an ice age. Rather, it is a single glaciation event within a long series of glaciations, collectively referred to under the term "ice age". More specifically, it is the eight glacial cycle in the current ice age, which has now lasted 2.58 million years. What this means is that all of the climatic changes that occurred at the end of the last glacial period have not only happened before, but have happened a total of seven times already. Not only that, but the previous glacials and interglacials have varied wildly in length and severity. Some of the previous glacials lasted far longer than the last one, while others were much shorter. Some were significantly more extreme, while others were milder. Just as an example, the previous cycle before ours included a particularly severe glacial giving way to an especially warm interglacial. In summary, all the species that existed at the end of the last glacial period were already perfectly well adapted to the coming and going of the glacials, having experienced and survived them countless times already. Only one single factor was different this time: Humans.
A depiction of typical Alaskan megafauna during the last interglacial, showing Mammuthus primigenius, the woolly mammoth, Mammut americanum, the american mastodon, and Bison latifrons, the long-horned bison. From the American Museum of Natural History
Okay, fine, the extinctions were not caused by climate change, enough of that already. How does this relate to the opening premise or the title for that matter? Who is "The Zoologist Who Cried Climate Change"?. Well, despite everything I have just listed, and despite the fact that pretty much every new study that's released serves to vindicate this idea, there is still a disturbingly large amount of people who continue to proclaim climate change as not only the most likely candidate, but in many cases the sole, confirmed cause, as if it were a fact. These people range from layman who are, understandably, ill-informed, to hobbyists and even many working scientists, including, yes, zoologists, though generally not people actually working in the field, for obvious reasons. The reasons for this continued belief are manifold, but generally relate to a sort of collective incredulity at the notion that us little, puny humans could really wipe out that many species. I concede that the idea that a small group of humans arrived to a new continent and then proceeded to wipe out tens of species across populations of millions of individuals is hard to wrap your head around, but all of the evidence that we have points towards it indeed having been the case. It being odd and disturbing does not detract from its reality.
Perhaps it is easier to understand, when one considers that wiping out a species is not just about butchering every last individual. Humans have a tendency of employing many hunting strategies, some of which are particularly destructive to large animals. For one, we may often target the vulnerable young of a given species, since they are easier to take down. If you're a dedicated K-strategist, meaning a species that relies on intensively caring for a small number of offspring that take a very long time to raise, you generally won't reach sexual maturity for many years, and will pour great amounts of time and energy into raising your young. As you might imagine, this makes K-strategists particularly vulnerable to human depredation, and unfortunately, most megafauna are indeed K-strategists. Another aspect of human hunting that makes us abnormally effective at wiping out species is our habit of altering the environment. In particularly, humans do seem to love employing fire, and especially in Australia, which is a very dry place, it appears that the early Aboriginal's use of fire essentially torched the entire continent, helping transform it from a relatively verdant and lush place to the dry and mostly barren land we know today. Fire is hard to escape, quick to spread, and can be quickly and effectively deployed to wipe out animals you don't like, especially if you have no intention of collecting the body afterwards. Know that a large population of particularly dangerous predators live in that forest? Just set it on fire and it'll sort itself out. Finally, a major aspect of human hunting that most people don't even think about, yet may in fact be the most key to our destructive effects on megafauna, is our predilection towards ranged weaponry. First the spear and then the bow, ranged weapons are incredibly dangerous for large animals, as they quite simply have no way of dealing with them. Even the largest and most imposing mammoth will die if you hit it with just a single well placed spear, which isn't particularly hard when your target is that big. Almost every single animal on the planet is adapted towards defending against mele attacks - teeth, claws, tails. Against a weapon such as a spear or an arrow, they have nothing.
Fire has been employed as a tool for managing the land since long before grouse moors, and has always been just as destructive.
Ultimately, the persistent belief in climate change as the causal factor does not seem to be exclusively a matter of evidence-based conviction. People want to believe in it, because it offers a simple and, more importantly, guilt-and responsibility-free solution. It's just so very, very convenient, that everything that happened in the past was out of our control and beyond our fault. Touting climate change as the perpetrator also serves to render the extinction of the megafauna as natural, just the way things are. It makes our current, denuded and ecologically devastated world okay, since it's the natural order. At the end of the day, the insistence upon climate change as the cause behind the extinctions, rather than an honest explanation for past events, is today little more than a form of denialism, up there with the deniers of genocides or present day climate change. It is pervasive because it gives people what they want, because it makes them feel good, lets them sleep easier at night by rendering them guilt-free. Fighting such a belief is hard, as one side uses evidence and the other emotions. Sadly, the battle of facts and feelings is often quite one sided, and it seems that educating people in this matter is and will forever be an uphill struggle.