The sixth mass extinction
Since life appeared on earth, there have been several mass extinctions in which many of the earth’s species were wiped out because of climate change, volcanic activity, the impact of an asteroid or reasons we have not yet discovered. The plants and animals which currently live on Earth have continued to evolve over the 65 million years since the last mass extinction. But many scientists consider the huge reduction in biodiversity since the emergence of humans is now on the scale of another mass extinction. This is known as the Holocene or Anthropocene extinction.
Ever more people need ever more space. Human activity continues to encroach on natural environments, thereby destroying the habitats of countless species. While some progress has been made in slowing the rate of loss of tropical forests and mangroves, serious declines are also being seen worldwide in freshwater wetlands, sea ice habitats, salt marshes, coral reefs, seagrass beds and shellfish reefs.
Ever more people need ever more stuff. Humankind’s relentless consumption of resources such as timber, oil and minerals is continuing to destroy natural habitats around the globe. We are also putting enormous pressure on populations of wild species, both by hunting in the developing world and by large-scale industrial fishing in our seas.
Ever more people need ever more homes. In most industrialised countries and a growing number of developing ones over half the population live in cities. Properly designed cities and agricultural systems can sometimes support people with a lower impact on biodiversity than can a more evenly spread population. But as our numbers rise, cities and industrial areas are growing and merging into each other, fragmenting the remaining habitat leaving isolated “islands” of natural populations of plants and animals too small to survive.
Ever more people need ever more food. In order to feed the numbers of people living on the Earth today, humanity has developed agricultural systems which rely on monocultures, artificial fertilisers and pesticides. Monocultures are increasingly susceptible to disease, pesticide use destroys insect populations indiscriminately, whilst fertiliser runoff pollutes water courses. In addition, the growing pressure on food supplies means an increasing proportion of agricultural land is farmed intensively, with fewer off seasons or fallow years in which to recover.
Ever more people produce ever more waste and pollution. As well as affecting the lives of humans, noise, light and chemical pollution can disrupt wildlife behaviour. Light from human activities makes it harder for predator species to catch their prey. Noise pollution interrupts both hunting and mating signals in many species, disturbing natural behaviour.
The build-up of phosphates and nitrates from agricultural fertilisers and sewage effluent is creating long-term algal blooms in freshwater lakes and inland water systems, causing fish stocks to decline, with serious implications for food security in many developing countries.
As populations increase, the disposal of waste becomes an increasingly serious issue. Pollution will always be a consequence, whether we use land fill, incinerators or disposal at sea and in watercourses. The disposal of toxic materials poses significant additional hazards and problems.
As a consequence of the introduction of non-native species to some areas, such as rabbits in Australia or goats on St. Helena, we have put many vulnerable ecosystems at risk, threatening native ecologies and diminishing biodiversity.