Environmental journalist Jeremy Hance, a regular contributor to ALERT, shares his perspectives on new research with big implications for Earth’s biological diversity.

Here’s a morbid question you’ve probably never been asked: Would you rather die from extreme heat or cold?

Conservationists are now facing a somewhat similar quandary.  Given the multitude of threats killing off species, conservationists must ask: Are more species dying from the age-old impacts on wildlife — habitat disruption and human overexploitation — or global warming?

Big Drivers of Change

A new study in Nature provides an answer, at least for the time being.  It’s still overexploitation and land-use change.

Examining threats to nearly 8,700 threatened or near-threatened species in the IUCN Red List, the researchers found that that the most important threat was crop farming, which threatened 54 percent of the species studied, followed by logging, which threatened 46 percent.

In contrast, climate-change impacts — which included extreme weather and heat waves ­– threatened only 19 percent of the species.  That’s around the same percentage as those threatened by overhunting.  Raising livestock actually threatens more species — 26 percent — than either of these threats.

The researchers, led by Sean Maxwell at the University of Queensland, warn that growing concerns about climate change should not dampen efforts to combat more traditional threats. Indeed, overall, the study found that 72 percent of surveyed species are threatened by human activities linked to commerce, subsistence, or recreation.

The research is backed up by previous studies.  For example a study in Nature in 2012 led by ALERT director Bill Laurance found that deforestation, logging, fires, and hunting were the biggest threats to species both inside and outside of tropical forest protected areas.  Pollution and climate change proved less important, at least over the past 2-3 decades, which was the interval over which the study was conducted.

Climate Change Still Important

This doesn’t mean conservationists can afford to be blasé about climate change.

For example, recent research estimates that if temperatures are allowed to rise two degrees above Celsius — the nominal target of the Paris Climate Agreement — we could lose 5.2 percent of all species on the planet.

That’s hundreds of thousands, potentially even millions, of species wiped out by climate change.

Moreover, a number of ecosystems — from coral reefs and cloud forests to Arctic sea ice and low-lying islands — are already proving particularly vulnerable to climate-change impacts.

In the recent study, Maxwell and colleagues noted that their findings might be hampered by the limitations of IUCN data.  For example, these data full of taxonomic holes.  While the IUCN has evaluated all known species of mammals, birds, and amphibians, other major groups have been left out, especially less charismatic assemblages such as fungi.

Moreover, it is likely that climate change impacts will only worsen with each passing year.  At some point down the road, climate change may overwhelm other threats.

Furthermore, many of the IUCN’s evaluations are several years or even decades old.  This lag-time means that current climate impacts may be underestimated for some species on the list.

Scary Synergisms

In the end, though, probably the most important thing to emphasize is that most species aren’t facing just one threat.

Maxwell’s study found that a stunning 80 percent of the species surveyed are under siege by more than one peril.  Hence, most species aren’t battling for survival against just overharvesting or agricultural expansion or infrastructure or climate change — but an increasingly lethal combination of two or more dangers at once.

A good analogy comes from boxing.  If humans were in a boxing match with nature, we’re not just giving nature an occasion jab — but a flurry of punches arriving all at once.  It’s this combination of interacting threats that can be so devastating for the survival of species.

For example, a 2008 paper in Ambio led by Mark Cochrane of South Dakota State University found that the synergism of logging, fire, and climate change could radically damage the Amazon.

By elevating temperatures and worsening droughts, climate change makes the Amazon more prone to burning.  Meanwhile, logging and habitat fragmentation make the tropical forest more likely to ignite and burn.  And burning in the Amazon, of course, releases large amounts of carbon dioxide, leading to greater global warming.

Together these three threats may prove far more lethal to the world’s greatest rainforest than if they acted independently.

Going Forward

Maxwell’s study urges conservationists not to ignore the ‘old’ threats of habitat loss, degradation, and species overexploitation.

These old threats, the authors argue, also have old solutions: More protected areas, better regulations and enforcement for hunting and harvesting, reducing the use of pesticides and fertilizers, public education, and reducing food waste, among others.

Finally, the authors argue that by combating the old perils, conservationists will buy species more time in an age of rapid climate change.  Tackling the pressing threats of habitat disruption and overharvesting today will reduce the chances of lethal synergisms tomorrow.

Fuente: http://alert-conservation.org/issues-research-highlights/2016/9/18/which-is-the-biggest-killer-climate-change-or-habitat-disruption