lunedì 22 giugno 2015

6th mass extinction! Homo stupidus!


In uno studio congiunto delle Università di Berkeley, Princeton e Stanford si sostiene che attualmente il tasso di estinzione dei vertebrati è 114 volte superiore al normale. Secondo gli studi di questi autorevoli scienziati siamo appena entrati in quella che sarà la sesta fase di estinzione di massa terrestre. Sembra quasi il titolo dell’ennesimo film catastrofista, invece è qualcosa di molto serio e documentato. Le tre prestigiose università americane hanno verificato che la velocità con la quale i vertebrati stanno progressivamente scomparendo dalla terra non ha eguali nelle cinque precedenti estinzioni di massa.
Lo studio è pubblicato su Science Advances e ve lo lascio come link nella descrizione del video. Ma vediamo un po’ quali sono i fatti. A partire dal 1900, secondo i dati della ricerca, sono più di 400 le specie di vertebrati che si sono definitivamente estinti. Questa cifra non sarebbe preoccupante se le estinzioni si fossero verificate in 10 mila anni, invece ne sono passati appena poco più di cento . Nel dettaglio si sono estinte 69 specie di mammiferi, 80 di uccelli, 24 di rettili, 146 di anfibi e 158 di pesci.
Ma la ricerca non riguarda solo le specie animali, ma anche l’uomo. Le cause di questa improvvisa accelerazione della percentuale di estinzione di massa sono anche tre dei più gravi problemi che riguardano noi umani: e cioè i cambiamenti climatici, l'inquinamento e la deforestazione. «Se consentiremo a tutto questo di continuare - ha detto Gerardo Ceballos, il coordinatore della ricerca - la vita avrà bisogno di molti milioni di anni per rigenerarsi e probabilmente la nostra stessa specie scomparirà». L'impatto dell'azione umana sull'ambiente ha causato una graduale ma inevitabile perdita della biodiversità ostacolando fondamentali processi biologici come l'impollinazione e la purificazione delle acque, indispensabili anche per l'uomo stesso. I ricercatori ritengono che se le cose continueranno ad andare in questa direzione entro tre generazioni umane l'impollinazione da parte delle api cesserà . Sembra una conclusione banale ma la loro scomparsa porterà scompensi incalcolabili all’ambiente e in particolare all’agricoltura, quindi, di conseguenza all’uomo.
There is no longer any doubt: we are entering a mass extinction that threatens humanity’s existence. That is the bad news at the center of a new study by a group of scientists including Paul Ehrlich, Bing Professor of Population Studies in biology and a senior fellow at the Stanford Woods Institute. Ehrlich and his co-authors call for fast action to conserve threatened species, populations and habitat, but warn that the window of opportunity is rapidly closing. “(The study) shows without any significant doubt that we are now entering the sixth great mass extinction event,” Ehrlich said. Although most well known for his positions on human population, Ehrlich has done extensive work on extinction going back to his 1981 book Extinction. He has long tied his work on coevolution; racial, gender and economic justice; and nuclear winter into the issue of wildlife populations and species loss. There is general agreement among scientists that extinction rates have reached levels unparalleled since the dinosaurs died out 66 million years ago. However, some have challenged the theory, believing earlier estimates rested on assumptions that overestimated the crisis. The new study, published in the journal Science Advances, shows that even with extremely conservative estimates, species are disappearing up to 114 times faster than the normal rate between mass extinctions, known as the background rate. “If it is allowed to continue, life would take many millions of years to recover, and our species itself would likely disappear early on,” said lead author Gerardo Ceballos of the Universidad Autónoma de México. Using fossil records and extinction counts from a range of records, the researchers compared a highly conservative estimate of current extinctions with a background rate estimate twice as high as those widely used in previous analyses. This way, they brought the two estimates – current extinction rate and average background or going-on-all-the-time extinction rate – as close to each other as possible. Focusing on vertebrates, the group for which the most reliable modern and fossil data exists, the researchers asked whether even the lowest estimates of the difference between background and contemporary extinction rates still justify the conclusion that people are precipitating “a global spasm of biodiversity loss.” The answer: a definitive yes. “We emphasize that our calculations very likely underestimate the severity of the extinction crisis, because our aim was to place a realistic lower bound on humanity’s impact on biodiversity,” the researchers write. Cause and Effect To history’s steady drumbeat, a human population growing in numbers, per capita consumption and economic inequity has altered or destroyed natural habitats. The long list of impacts includes: land clearing for farming, logging and settlement introduction of invasive species carbon emissions that drive climate change and ocean acidification toxins that alter and poison ecosystems. Now, the specter of extinction hangs over about 41 percent of all amphibian species and 26 percent of all mammals, according to the International Union for Conservation of Nature, which maintains an authoritative list of threatened and extinct species. “There are examples of species all over the world that are essentially the walking dead,” Ehrlich said. As species disappear, so do crucial ecosystem services such as honeybees’ crop pollination and wetlands’ water purification. At the current rate of species loss, people will lose “many” biodiversity benefits within three generations, the study’s authors write. “We are sawing off the limb that we are sitting on,” Ehrlich said. Hope for the Future Despite the gloomy outlook, there is a meaningful way forward, according to Ehrlich and his colleagues. “Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species, and to alleviate pressures on their populations—notably habitat loss, over-exploitation for economic gain, and climate change.” the study’s authors write. In the meantime, the researchers hope their work will inform conservation efforts, the maintenance of ecosystem services, and public policy.