1. Climate change

Changes in climate throughout our planet's history have, of course, altered life on Earth in the long run — ecosystems have come and gone and species routinely go extinct.

But rapid, manmade climate change speeds up the process, without affording ecosystems and species the time to adapt. For example, rising ocean temperatures and diminishing Arctic sea ice affects marine biodiversity and can shift vegetation zones, having global implications.

Overall, climate is a major factor inthe distribution of speciesacross the globe; climate change forces them to adjust. But many are not able to cope, causing them to die out.

2. Deforestation and habitat loss

Deforestation is a direct cause of extinction and loss of biodiversity. An estimated18 million acresof forest are lost each year, due in part to logging and other human practices, destroying the ecosystems on which many species depend.

Tropical rainforests in particular, such as theAmazon, hold a high percentage of the world's known species, yet the regions themselves are in decline due to humans.

3. Overexploitation

Overhunting, overfishing and over-harvesting contribute greatly to the loss of biodiversity, killing off numerous species over the past several hundred years. Poaching and other forms of hunting for profit increase the risk of extinction; the extinction of an apex predator — or, a predator at the top of a food chain — can result incatastrophic consequencesfor ecosystems.

5. Pollution

From the burning of fossil fuels (releasing dangerous chemicals into the atmosphere and, in some cases, depleting ozone levels) to dumping19 billion pounds of plasticinto the ocean every year, pollution completely disrupts the Earth's ecosystems. While it may not necessarily cause extinction, pollutants do have the potential to influents species' habits.

For example, acid rain, which is typically caused by the burning of fossil fuels, can acidify smaller bodies of water and soil, negatively affecting the species that live there bychangingbreeding and feeding habits.