The 'great dying': rapid warming caused largest extinction
event ever, report says
Up to 96% of all marine species and more than two-thirds of
terrestrial species perished 252m years ago
Oliver Milman in New York
@olliemilman
Thu 6 Dec 2018 19.00 GMT Last modified on Thu 6 Dec 2018
19.05 GMT
https://www.theguardian.com/environment/2018/dec/06/global-warming-extinction-report-the-great-dying
Researchers say spike in Earth’s temperatures led to demise of
marine life and warned that present-day global warming will also have severe
ramifications.
A model in the study
mimicking conditions in the Permian period suggests marine animals essentially
suffocated in the warming waters. Photograph: John Raoux/AP
Rapid global warming caused the largest extinction event in
the Earth’s history, which wiped out the vast majority of marine and
terrestrial animals on the planet, scientists have found.
The mass extinction, known as the “great dying”, occurred
around 252m years ago and marked the end of the Permian geologic period. The
study of sediments and fossilized creatures show the event was the single
greatest calamity ever to befall life on Earth, eclipsing even the extinction
of the dinosaurs 65m years ago.
Up to 96% of all marine species perished while more than
two-thirds of terrestrial species disappeared. The cataclysm was so severe it
wiped out most of the planet’s trees, insects, plants, lizards and even
microbes.
Scientists have theorized causes for the extinction, such as
a giant asteroid impact. But US researchers now say they have pinpointed the
demise of marine life to a spike in Earth’s temperatures, warning that
present-day global warming will also have severe ramifications for life on the
planet.
“It was a huge event. In the last half a billion years of
life on the planet, it was the worst extinction,” said Curtis Deutsch, an
oceanography expert who co-authored the research, published on Thursday, with
his University of Washington colleague Justin Penn along with Stanford
University scientists Jonathan Payne and Erik Sperling.
The researchers used paleoceanographic records and built a
model to analyse changes in animal metabolism, ocean and climate conditions.
When they used the model to mimic conditions at the end of the Permian period,
they found it matched the extinction records.
According to the study, this suggests that marine animals
essentially suffocated as warming waters lacked the oxygen required for
survival. “For the first time, we’ve got a whole lot of confidence that this is
what happened,” said Deutsch. “It’s a very strong argument that rising
temperatures and oxygen depletion were to blame.”
The great dying event, which occurred over an uncertain
timeframe of possibly hundreds of years, saw Earth’s temperatures increase by
around 10C (18F). Oceans lost around 80% of their oxygen, with parts of the
seafloor becoming completely oxygen-free. Scientists believe this warming was
caused by a huge spike in greenhouse gas emissions, potentially caused by
volcanic activity.
The new research, published in Science, found that the drop
in oxygen levels was particularly deadly for marine animals living closer to
the poles. Experiments that varied oxygen and temperature levels for modern
marine species, including shellfish, corals and sharks, helped “bridge the gap”
to what the model found, Payne said.
“This really would be a terrible, terrible time to be around
on the planet,” he added. “It shows us that when the climate and ocean
chemistry changes quickly, you can reach a point where species don’t survive.
It took millions of years to recover from the Permian event, which is
essentially permanent from the perspective of human timescales.”
Over the past century, the modern world has warmed by around
1C due to the release of greenhouse gases from the burning of fossil fuels such
as coal, oil and gas, rather than from volcanic eruptions.
This warming is already causing punishing heatwaves,
flooding and wildfires around the world, with scientists warning that the
temperature rise could reach 3C or more by the end of the century unless there
are immediate, radical reductions in emissions.
At the same time, Earth’s species are undergoing what some
experts have termed the “sixth great extinction” due to habitat loss, poaching,
pollution and climate change.
“It does terrify me to think we are on a trajectory similar
to the Permian because we really don’t want to be on that trajectory,” Payne
said. “It doesn’t look like we will warm by around 10C and we haven’t lost that
amount of biodiversity yet. But even getting halfway there would be something
to be very concerned about. The magnitude of change we are currently
experiencing is fairly large.”
Deutsch said: “We are about a 10th of the way to the
Permian. Once you get to 3-4C of warming, that’s a significant fraction and
life in the ocean is in big trouble, to put it bluntly. There are big
implications for humans’ domination of the Earth and its ecosystems.”
Deutsch added that the only way to avoid a mass aquatic
die-off in the oceans was to reduce carbon emissions, given there is no viable
way to ameliorate the impact of climate change in the oceans using other
measures.
The research group “provide convincing evidence that warmer
temperatures and associated lower oxygen levels in the ocean are sufficient to
explain the observed extinctions we see in the fossil record”, said Pamela
Grothe, a paleoclimate scientist at the University of Mary Washington.
“The past holds the key to the future,” she added. “Our
current rates of carbon dioxide emissions is instantaneous geologically
speaking and we are already seeing warming ocean temperatures and lower oxygen
in many regions, currently affecting marine ecosystems.
“If we continue in the trajectory we are on with current
emission rates, this study highlights the potential that we may see similar
rates of extinction in marine species as in the end of the Permian.”
Maior extinção da história da Terra aconteceu devido às
alterações climáticas
O estudo divulgado pela revista Science revela que a
extinção em massa que ocorreu há 252 milhões de anos foi causada pelo
aquecimento global. 96% das espécies marinhas foram exterminadas.
LUSA 7 de Dezembro de 2018, 2:21
A maior extinção da história na Terra, que marcou o fim do
período permiano, há cerca de 252 milhões de anos, foi causada por alterações
climáticas, indica uma investigação divulgada na edição desta sexta-feira da
revista Science.
A extinção no final do permiano, no fim da era paleozóica e
muito antes dos dinossauros, aconteceu quando o planeta estava repleto de
plantas e animais, que foram praticamente extintos.
Fósseis em rochas no leito dos mares mostram um ecossistema
marinho diversificado e próspero, seguido de uma faixa de cadáveres.
Cerca de 96% das espécies marinhas foram exterminadas, sendo
necessários milhões de anos para a vida se multiplicar e diversificar de novo.
Até agora têm sido debatidos os motivos que tornaram os
oceanos inóspitos, se o aumento da acidez, se o envenenamento dos mares, se a
falta de oxigénio ou se o aumento das temperaturas.
A nova pesquisa agora divulgada, das universidades de
Washington e de Stanford, nos Estados Unidos da América, combinando modelos das
condições oceânicas e do metabolismo animal, com dados laboratoriais e registos
paleoceanográficos, indica que a extinção em massa nos oceanos foi causada pelo
aquecimento global, deixando os animais sem possibilidade de respirar.
O estudo, publicado na edição de hoje da revista científica
Science, explica que à medida que as temperaturas aumentavam e o metabolismo
dos animais acelerava as águas mais quentes não podiam conter oxigénio
suficiente para que sobrevivessem.
"Esta é a primeira vez que temos uma previsão
mecanicista sobre o que causou a extinção, que pode ser directamente testada
com os registos fósseis, o que nos permite fazer previsões sobre as causas de
uma extinção no futuro", disse o principal autor da investigação, Justin
Penn.
Os investigadores criaram um modelo climático com a
configuração da Terra no período permiano e dizem que antes das erupções
vulcânicas na Sibéria criarem um planeta de gases com efeito de estufa os
oceanos tinham temperaturas e níveis de oxigénio semelhantes aos de hoje.
O passo seguinte foi aumentar os gases com efeito de estufa
a um nível que as temperaturas dos oceanos também subissem e quando tal
aconteceu os oceanos, no modelo, perderam 80% do oxigénio, com as zonas mais
profundas a ficarem mesmo sem nenhum oxigénio.
Dizem os especialistas que a tolerância dos animais de hoje
a altas temperaturas e baixo oxigénio será semelhante à dos animais do período
permiano, já que evoluírem em condições ambientais semelhantes.
Sem comentários:
Enviar um comentário