Climate change is multiplying existing threats to much of the natural world, and more species face an unparalleled extinction risk.
 |
| Africa's lions number only 10% of those the continent could sustain. Image: Luca Galuzzi via Wikimedia Commons |
They point out that at a conservative estimate the economic benefits of biodiversity – the collective word for all the richness of the planet's species – are at least 10 times the cost of conservation of that biodiversity.
And yet, they report, human actions already threaten a quarter of all mammal species and 13% of all birds. An estimated 21,000 plants and other kinds of animal are known to be at risk.
In one of the world's richest habitats of all – the terrain where south-east Asia, India and China meet – people in the last 50 years have put at risk two thirds of all mammals that weigh more than 10kg.
This summary of waste and despoliation is in a series of papers in the journal Nature, one of which looks again at the threats to biodiversity, while another concentrates on the ways people influence and depend on the fruits of three billion years of natural evolution.
Human pressure
It is a given that human economies depend entirely on what grows on the planet, and what can be excavated from its soils. The clearing of the forests and the settlement of the grasslands, pollution from the cities, overhunting and overgrazing, all driven by the swelling of human numbers, have now taken rates of species extinction to alarming levels.
Climate change, too, has now become a factor: it has been linked to the potential extinction of species, and to the obliteration of species in particular regions.
It has also been identified as a danger to the diversity of plant life as temperatures rise and rainfall patterns change with rising ratios of atmospheric carbon dioxide, the greenhouse gas emitted from internal combustion engines and coal-fired power stations.
No one yet claims that climate change itself is the principal hazard, but it exacerbates the impact of all the other pressures on wildlife.
Tropical targets
So a team led by David Tilman of the University of Minnesota has delivered a paper looking at the next 50 years, as human impact on habitat poses, they say "unprecedented levels of extinction risk on many more species worldwide" – especially the large mammals of tropical Africa, Asia and South America.
The world had lost half of its terrestrial mammalian megafauna – mammals heavier than 44kg – by 1,000 BC, and 15% of all bird species. In the last 3,000 years human numbers have multiplied 25-fold and another 4bn of us will join the human race by the century's end. So, the scientists argue, unless steps are taken, extinction rates will accelerate.
But, they point out, some steps are being taken: 31 bird species have been saved by conservation programmes from total extinction, and the same efforts have halted the decline of one threatened vertebrate in five. Captive breeding programmes have reintroduced species that were once all but lost.
But there is much more to be done: lion numbers in Africa, for instance, have fallen to one-tenth of their potential.
And in a second paper, a team led by Forest Isbell of the University of Minnesota and backed by co-authors from eight nations on four continents, instances the benefits of conservation.
"Human activities are driving the sixth mass extinction in the history of life on Earth, despite the fact that diversity of life enhances many benefits people reap from nature"Biodiversity in the form of trees and scrubland saves humans up to US$3 trillion just as carbon storage: that is, it keeps dangerous levels of carbon out of the atmosphere.
At a practical finance level, the calculated value of biodiversity to commercial forest productivity is set at between $166bn a year and $490bn.
Right now, the world spends about $25bn a year on conservation. It would cost $76bn annually to meet all the world's conservation targets. And, the authors point out, a cash value simply cannot be set on many of biodiversity's blessings. Some things are priceless.
"Human activities are driving the sixth mass extinction in the history of life on Earth, despite the fact that diversity of life enhances many benefits people reap from nature, such as wood from forests, livestock forage from grasslands, and fish from oceans and streams," said Dr Isbell. "It would be wise to invest much more in conserving biodiversity."
*Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.
Links
- Climate's muted wildlife extinction threat
- Future threats to biodiversity and pathways to their prevention
- Global warming already causing local extinctions
- Plant biodiversity at risk as climate changes
- Man-made climate change increases extinction dangers
- We're on the brink of mass extinction -- but there's still time to pull back
- Linking the influence and dependence of people on biodiversity across scales
No comments:
Post a Comment