For many decades scientists have warned that
For many decades, scientists have warned that human activity is pushing life on our planet beyond the point of no return. In the Earth\'s history there have been five mass extinction events, most recently the Cretaceous–Tertiary mass extinction that occurred almost 65 million years ago and was thought to have been caused by the massive impact of an asteroid on Planet Earth. In the 21st century, we face a sixth mass extinction. According to an published in July by Gerardo Ceballos and colleagues, the Earth is experiencing a huge decline in species\' populations and a great reduction in their range that could have profound effects on the ecosystems on which human civilisation depends. They found that about 30% of land vertebrates including reptiles, birds, and order Axitinib are experiencing a decline and losses in local population. In some parts of the world they are losing 70% of their species because of habitat degradation. The authors describe their findings as a biological annihilation, claiming that the sixth mass extinction might be already underway.
But this time is fundamentally different from the past. While previous extinctions were driven by physical phenomena, such as natural climate change, volcanic eruptions, ocean acidification, and meteorites, the sixth has its roots in human activity. The arrival of almost 200 000 years ago changed the global ecosystem\'s equilibrium and overturned the natural laws that govern the Earth. A new trajectory was set for the planet. Different from other species, humans developed the ability to predominate over all other species and exploit the net primary resources of the planet. They started to overhunt animals and fish, use fossil fuels for the production of energy, and exploit the natural resources of the planet in such a way that today the ability of other species to survive has been profoundly undermined.
The world lost about 2·3 million km of forest during the first 12 years of the 21st century, with loss of tropical forest outpacing that of other forest types. Agricultural expansion and wood extraction are among the leading causes of tropical deforestation, and some human populations clearly benefit from increased food, fuel, wood, and fibre production. But what is the cost? In recognition of the profound, long-term effect of deforestation on emissions of greenhouse gases and the global climate, in 2008 the UN established the Programme on Reducing Emissions from Deforestation and Forest Degradation. The effects of deforestation on climate, however, seem quite distant, reducing the urgency to take action. But what if forest destruction directly and immediately affected child health? What if setting aside forests in protected areas near human communities prevented childhood illnesses? Would that change local, regional, or large-scale forest-management policies for human wellbeing? In an important new study published in this issue of , Thomas Pienkowski and colleagues address the effects of protected areas and forest destruction on human health in 35 547 households in Cambodia over 10 years. The authors recognise that substantial attention has been paid to the human health consequences of ecosystem changes. However, they point out that, by and large, previous scientific studies were focused on individual health consequences (eg, a specific infectious disease). Although this specificity is in some ways a virtue, it also limits the ability to draw broad conclusions about the net effects of habitat-destroying development projects on the overall health of local communities. Pienkowski and colleagues cast a much broader net: they analyse changes in diarrhoea, acute respiratory infections, and fever in children, which are associated with the amount of local land set aside in protected areas, and with the destruction of local forests. Diarrhoeal diseases and acute respiratory infections decreased with increasing size of local protected areas, and all three childhood disease categories increased with the extent of local loss of dense forest.