UNBELIEVABLE: Cool pretty nature pics - The Untold Story

There are certain people who believe the world revolves around them, and that they are the only ones on the planet. Imagine their surprise when they come to learn that we actually share Earth with millions of other people, animals, plants and organisms.

The IUCN Red List contains 2.17 million species, including one million insects, over 11,000 birds, over 12,000 reptiles, and over 6,000 mammals. And those are only the ones we know about. Plus, researchers are divided when it comes to the actual numbers.

"If some alien version of the Starship Enterprise visited Earth, what might be the visitors' first question? I think it would be: 'How many distinct life forms—species—does your planet have?' Embarrassingly, our best guess answer would be in the range of 5 to 10 million eukaryotes (never mind the viruses and bacteria), but we could defend numbers exceeding 100 million, or as low as 3 million," wrote Robert May in a paper published in Science.

This drives home the point that we might never really know the exact answer. But the bottom line is: human beings are not alone on the planet. Not by a long shot.

Yet, of all the millions of species on Earth, it's humans that are causing the most destruction. It's no secret that our planet is in crisis.

"Land is degrading fast. Biodiversity is declining at an unprecedented rate. The climate is growing more extreme and unpredictable," warns the United Nations Development Programme (UNDP) in a special feature published this year.

"Our planet is on the brink of irreversible changes that will reshape the systems that sustain life: from the way we grow food and manage water, to how communities build livelihoods and prepare for an uncertain future," it adds.

According to the UNDP, up to 40% of the world's land is degraded. It's a staggering percentage with dire consequences. "Addressing land degradation is not only about restoring ecosystems. It is about protecting livelihoods," reads the feature, noting that the negative effects are being felt through food insecurity, water scarcity, migration and economic instability.

While you and I scroll through these beautiful images of nature, experts are warning that if we don't act fast, many species may one day cease to exist. The UNDP calls it an "unprecedented biodiversity crisis," adding that ecosystems and species are declining at alarming rates.

It explains that this threatens food systems, water security, health, livelihoods and economic stability, as well as our capacity to tackle climate change. And here's another scary thought: The IUCN Red List reveals that the number of recent extinctions documented on its Extinct (EX) and Extinct in the Wild (EW) categories is likely to be a "significant underestimate."

"The rapid loss of species we are seeing today is estimated by experts to be between 1,000 and 10,000 times higher than the natural extinction rate," warns the World Wildlife Fund (WWF).

And for those who don't feel at least partly responsible, the WWF adds that, "Unlike the mass extinction events of geological history, the current extinction challenge is one for which a single species - ours - appears to be almost wholly responsible."

Just like the UNDP, the World Wildlife Fund has rung some major alarm bells. "There can be little debate that there is, in fact, a very serious biodiversity crisis," the site notes.