The definition of biodiversity (i.e. biological diversity) is the variety and variability of all life on Earth, including microbes, fungi and plants as well as animals including humans. There are multiple levels of biodiversity, starting with genetic variability, zooming out to the species-level, ending with ecosystem-level diversity. It is important to maintain variation within a species to allow them to be better equipped to deal with changes in the environment, but also to conserve all diversity of species as this is crucial for healthy ecosystems.

Ecosystems are complex and different levels within the system are all interdependent on each other. This means that every species on the planet has its own role within an ecosystem, and that the decline or increase of one species due to a big change in the environment can have effects on the entire ecosystem. For example, fruit-eating monkeys, bats, and birds are crucial for dispersing the seeds of trees that are important for removing carbon dioxide from the atmosphere.

Healthy ecosystems are crucial for every living being on the planet, including humans. Ecosystem services (i.e. services that the planet give us humans) include oxygen production, as well as providing food, water, fuel and shelter. There are also numerous underrated ecosystem services like pollination, seed dispersal, climate regulation, water purification and pest control that are fully taken care of by mother nature, and absolutely essential for human existence. We depend a whole lot more on healthy ecosystems than ecosystems depend on humans, and maintaining biodiversity is key to healthy ecosystems. In Europe only, the loss of biodiversity has costs us about 450 million euro’s a year.

Moreover, we only scratched the surface of our discovery of all peculiarities and ingeniousness of life on Earth. It is expected that there are a great number of adaptations, medicinal herbs, and ecosystem benefits that may not have been discovered yet that can be useful to humans. In addition to utilitarian value, biodiversity also has intrinsic value, meaning its inherent worth, and there are many ethical and moral reasons as to why we should conserve biodiversity.

Human activities, most importantly: deforestation, pollution, invasive species, climate change, the use of pesticides and insecticides have caused a massive loss in biodiversity in the last century and long-lasting changes within ecosystems. It’s tricky to estimate how many species we are losing, as we don’t even know how many there are out there exactly. Moreover, the extinction of species is a natural process. Currently, researchers estimate that we are losing species at least 100 times higher than the background extinction rate as predicted in a scenario without humans.

A mass extinction is a widespread and rapid decrease in biodiversity. The most widely accepted number of mass extinctions that Earth has faced since it’s creation 4.54 billion years ago is at least five. The worst mass extinction (at the end of the Permian) killed 96% of all species and lasted between 11-108 thousand years. Experts in the field have declared that the we have entered a sixth mass extinction that is entirely caused by humans – the Anthropocene extinction. Out of the estimated 8 million species, 1 million plants and animals are threatened with extinction and vertebrates have declined on average 60% since 1970. Extinctions have been increasing exponentially since the 20th century specifically, see below.

Highly conservative measure of cumulative vertebrate species recorded as extinct or extinct in the wild by the IUCN (2012). The graph shows the percentage of extinct species within mammals (total evaluated = 5513), birds (total evaluated = 10,425), reptiles (total evalutted = 4414), amphibians (total evaluated = 6414), fishes (total evaluated = 12,457) and all vertebrates combined (total evalutated = 39,223). The background line in dashes is the extinction rate as you expect under a constant standard background rate of 2 E/MSY (the extinction probability averaged over species-years). Results and figure from Ceballos et al. 2015.

But, there is still debate on whether we have entered the Sixth Mass Extinction or are on the brink of it. This is mostly because when you base the number of extinct species on the IUCN Red List – the list of all threatened species on Earth – you are not including all species on Earth. The IUCN Red List mostly contains mammals and birds, but only a fraction of all invertebrates – the animal group that make up [97%](https://www.nationalgeographic.com/animals/invertebrates#:~:text=This is by far the,millions more to be discovered.) of all animals on Earth! A recent study that calculated the rate of species loss of a big group of invertebrates estimated this rate to be over 200 times higher than the one based on the IUCN-Red List! Whether we agree or not that we have entered a Sixth Mass Extinction – the huge loss in biodiversity caused by human activity is undeniable.

Even though the evidence points quite clearly to human activity driving climate change and rapid extinctions, it’s good to stay critical and wonder how we can really know if the biodiversity crisis is indeed our fault.

One of the main difficulties in understanding the biodiversity crisis is that there are a lot of different factors that play a role, and we can never accurately compare the state of the planet at this time of age to what it would be like without humans. So, how can we know that human activity is the cause of the rapid extinction? Scientists try to address this question by building sophisticated models that can take apart those different factors, such as how greenhouse gases, volcanoes and solar radiation affect global temperatures separately and combined.

Global mean surface temperatures from Berkeley Earth (black dots) and modelled influence of different radiative forcings (colored lines), as well as the combination of all forcings (grey line) for the period from 1850 to 2017. See methods at the end of the article for details. Chart by Carbon Brief using Highcharts from Carbonbrief.

From this study, we can see that the most likely factor that is driving the increase in global temperatures is the increase in greenhouse gases, which is a direct consequence of human activities. Similar models can be applied to the loss of biodiversity, pointing in the same direction.

One of the key things at this time of age is to reduce the exponential increase in overpopulation, deforestation, resource use and pollution. We have to protect areas, not only biodiversity hotspots (the 36 places on Earth that represent only 2.5% of Earth’s land surface, but contain nearly 43% of endemic birds, mammals, reptiles and amphibians), but also locally important ecosystems. Habitats also have to stay connected so organisms can safely move from one to the other and find mates, e.g. through making natural corridors. Check out the projects we have donated to in the past!

Not only do we have to conserve what we have left, but also through restoration, reintroduction and regeneration of natural areas. This can be done through e.g. controlling invasive species, but also by reintroducing species that have cascading effects on the entire ecosystem (such as a top-predator like the wolf, check out this classic example of how reintroducing wolves changed rivers in Yellowstone National Park). Restoration and regeneration projects may focus on making dry, lifeless areas (e.g. due to deforestation) spring to life again by planting trees and creating fertile land, providing food security, and strengthen climate resilience (i.e. making sure that it’s adapt to changes in climate). Check out the projects we have donated to in the past!