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One question is how much this is due to human activity:
Futures Forum: Climate change: Entering the Anthropocene
Another is how far things have gone:
Futures Forum: Climate change: tipping point
The university of Edinburgh has just published findings that point to a new 'great extinction':
Greatest extinction driven by acidic oceans
Changes to Earth’s oceans, caused by volcanic activity, triggered the greatest extinction of all time, a study shows.
The event, which took place 252 million years ago, wiped out more than 90 per cent of marine species and more than two-thirds of the animals living on land.
It happened when Earth’s oceans absorbed huge amounts of carbon dioxide from volcanic eruptions.
This changed the chemical composition of the oceans - making them more acidic - with catastrophic consequences for life on Earth.
Soaring emissions
The study, co-ordinated by University researchers, is the first to show that highly acidic oceans were to blame.
The findings are helping scientists understand the threat posed to marine life by modern-day ocean acidification.
The amount of carbon added to the atmosphere that triggered the mass extinction was probably greater than today's fossil fuel reserves.
However, the carbon was released at a rate similar to modern emissions. This fast rate of release was a critical factor driving ocean acidification.
Unstable ecosystem
The Permian-Triassic Boundary extinction took place over a 60,000 year period. Acidification of the oceans lasted for around 10,000 years.
Ocean acidification was the driving force behind the deadliest phase of the extinction, which dealt a final blow to an already unstable ecosystem.
Increased temperatures and widespread loss of oxygen in the oceans had already put the environment under pressure.
Scientists have long suspected that an ocean acidification event occurred during the greatest mass extinction of all time, but direct evidence has been lacking until now. This is a worrying finding, considering that we can already see an increase in ocean acidity today that is the result of human carbon emissions.Dr Matthew ClarksonSchool of GeoSciences
Chemical change
Oceans can absorb some carbon dioxide but the large volume released - at such a fast rate - changed the chemistry of the oceans.
The mass extinction of both marine and land-based animals demonstrates that extreme change took place in all of Earth’s ecosystems.
The team analysed rocks unearthed in the United Arab Emirates - which were on the ocean floor at the time - to develop a climate model to work out what drove the extinction.
The rocks preserve a detailed record of changing oceanic conditions at the time.
Unique team
The study, published in the journal Science, was carried out in collaboration with the University of Bremen, Germany, and the University of Exeter, together with the Universities of Graz, Leeds, and Cambridge.
Funding was provided by the the International Centre for Carbonate Reservoirs, Natural Environmental Research Council, Leverhulme Trust, German Research Foundation and the Marsden Fund.
This work was highly collaborative and the results were only possible because we assembled a unique team of geochemists, geologists and modellers to tackle an important and long-standing problem.Professor Rachel WoodSchool of GeoSciences
Greatest extinction driven by acidic oceans | News |
The press has taken up the story:
Greatest mass extinction driven by acidic oceans, study finds -- ScienceDaily
Good news: Scientists, including Professor Rachel Wood of the University of Edinburgh, have found out that ocean acidification caused history's biggest extinction | Metro News
Ocean acidification killed off more than 90 per cent of marine life 252 million years ago, scientists believe
Researchers say the oceans suddenly became more acidic, making it impossible for the vast majority of sea creatures to survive
SCIENCE EDITOR Thursday 09 April 2015
In a disturbing parallel to what is happening in the sea today, researchers have found chemical signatures in ancient rock formations showing that the oceans at that time suddenly became more acidic, making it impossible for the vast majority of sea creatures to survive.
Scientists believe that the dramatic acidification of the oceans at the end of the Permian period was caused by the continual eruption of super-volcanoes which generated the release of massive volumes of carbon dioxide at a rate comparable to the levels of CO2 that humans are pumping into the atmosphere at the present time.
“The important take-home message of this is that the rate of increase of CO2 during the Permian mass extinction is about the same rate as the one to which we are exposing the ocean to today,” said Professor Rachel Wood of the University of Edinburgh. We have found that the oceans 252 million years ago experienced dramatic acidification and that this coincided with a significant rise in carbon dioxide levels. The data is compelling and we really should be worried in term of what is happening today,” Professor Wood said.
The Great Dying marked the end of the Permian and beginning of the Triassic period, which is why it is also known at the P-T extinction. It was the biggest of the five mass extinctions on Earth, killing off 51 per cent of all marine families, 82 per cent of all genera and between 93 and 97 per cent of all species. Although the oceans suffered badly – reef-building corals for instance went extinct – it also affected terrestrial life-forms, such as insects, which suffered the only mass extinction in their long history, and primordial forests, which virtually disappeared from the surface of the Pangaea supercontinent that stretched from pole to pole.
Scientists believe that early forms of life that existed at that time were already under some stress as a result of the eruption of a network of super-volcanoes called the Siberian Traps, which lasted for up to a million years. One of the effects of this phenomenon was to raise global temperatures and cause significant oxygen depletion in the oceans, making life difficult for Permian marine creatures such as giant sea scorpions and trilobites. The scientists said the P-T extinction was divided into an early die-off, possibly caused by oxygen starvation, and a second, later extinction caused by a dramatic increase in ocean acidity resulting from carbon dioxide in the atmosphere forming carbonic acid when it dissolves in seawater.
Reef-building corals for instance went extinct (Getty Images)
“The oceans at that time were definitely starved of oxygen, and we know that for sure. It was complicated because there were several things going on then and they were taking place at different times,” Professor Wood said. “We don’t exactly know what the relation was between the eruption of the Siberian Traps, the production of CO2, global warming and the oceans being starved of oxygen – but we believe there was a relationship,” she said.
A study of ancient rocks from the deserts of the United Arab Emirates, which were formed on the ocean floor 250 million years ago, have revealed that the proportion of boron isotopes within the rock changed significantly, indicating a rapid shift in the pH or acidity of the surrounding seawater. This the first real evidence that ocean acidification happened on a dramatic scale at the end of the Permian period, suggesting that it must have played a decisive and possibly final role in killing off the species that were still managing to hang on through all the other environmental assaults they went through during that time, the scientists said.
“Scientists have long suspected that an ocean acidification event occurred during the greatest mass extinction of all time, but direct evidence had been lacking until now,” said Matthew Clarkson of Edinburgh University, the first author of the study published in the journal Science. “This is a worrying finding, considering that we can already see an increase in ocean acidity today that is the result of human carbon emissions.”
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