In 2007, the IPCC warned that “as global average temperature increase exceeds about 3.5°C [relative to 1980 to 1999], model projections suggest significant extinctions (40-70% of species assessed) around the globe.”  On our current emissions path, we will warm far more than that this century, which suggests we risk the high end of species loss.

A new Science study (subs. req’d) confirms this risk.  It examines “the pace of diversity loss leading to the Triassic-Jurassic boundary (TJB).”  It finds “the sudden diversity drop … coincided with a mere ~100 to ~350 ppmv rise in CO2 concentration,” and “CO2-induced global warming was likely an important contributory factor to plant species turnover at the TJB.”

The study notes “The abrupt plant diversity loss … is consistent with expected plant responses to a catastrophically rapid rather than gradual environmental change,” such as might be caused from a massive release of methane. Good thing homo “sapiens” sapiens isn’t doing anything that might bring about catastrophically rapid climate change, like say 5°C warming in one century or a massive release of methane (see NOAA stunner: “Methane levels rose in 2008 for the second consecutive year after a 10-year lull”).

Worse, the study concludes:

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An alternative explanation for the abrupt diversity loss is that it represents a threshold response of LT vegetation to relatively minor increases in CO2 concentration and/or global temperature.

Again, we are quite literally playing with fire here, risking massive species loss this century if we don’t sharply reverse greenhouse gas emissions trends soon.

And, of course, “When CO2 levels in the atmosphere reach about 500 parts per million, you put calcification out of business in the oceans.” There aren’t many studies of what happens to the oceans as we get toward 800 to 1000 ppm, but it appears likely that much of the world’s oceans, especially in the southern hemisphere, become inhospitable to many forms of marine life. A 2005 Nature study concluded these “detrimental” conditions “could develop within decades, not centuries as suggested previously.”

A 2009 study in Nature Geoscience warned that global warming may create “dead zones” in the ocean that would be devoid of fish and seafood and endure for up to two millennia (see Ocean dead zones to expand, “remain for thousands of years”).

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Let me end with a long excerpt from a article on the new Science study, “Extinction risk to plant biodiversity may occur at lower levels of atmospheric CO2 than previously considered,” for those without a subscription:

According to the findings published in the leading journal Science, the current estimated levels of atmospheric carbon dioxide which are thought to lead to sudden biodiversity loss may have to be revised downwards.

However, the scientists from University College Dublin, The Smithsonian Institute in Washington DC and Oxford University, have cautioned that their study findings may not have accounted for additional atmospheric gases such as sulphur dioxide which may have emerged from extensive volcanic emissions at the time to also play a role in driving the rise in the Earth’s temperature.

“Examining the 200 million year old fossil leaves from East Greenland, we discovered that the ancient biodiversity crash happened at atmospheric greenhouse gas levels of approximately 900 parts per million,” said Dr Jenny McElwain from the UCD School of Biology and Environmental Science at University College Dublin, Ireland, the lead researcher on the project.

“If we continue with the current intensive use of fossil fuel energy, some estimates calculate that carbon dioxide levels in the earth’s atmosphere will reach 900 parts per million by the year 2100. This is exactly the same levels at which our study identified the mass biodiversity collapse in ancient Greenland.” But according to Dr McElwain, this is a worst case scenario.

“Clearly, our study on ancient ecosystems shows that we must take heed of the early warning signs of deterioration within modern ecosystems, as we have seen from the past that very high levels of species extinctions – as high as 80% – can take place very suddenly although preceded by long intervals of ecological change,” she explains.

The time to act is now (see U.S. media largely ignores latest warning from climate scientists: “Recent observations confirm … the worst-case IPCC scenario trajectories (or even worse) are being realised” – 1000 ppm).