Over recent years, concern about a coming hothouse mass extinction set off by human carbon emissions has been on the rise. Studies of Earth’s deep history reveal that at least 4 out of the 5 major mass extinctions occurred during both hothouse periods and during times when atmospheric and oceanic carbon spiked to much higher than normal ranges. Now a new scientific study reveals that we have already emitted 50 percent of the carbon needed to set off such a major global catastrophe.

Fossil Fuel Burning = Race Toward a 6th Mass Extinction

The primary driver of these events is rising atmospheric CO2 levels — often caused in the past by the emergence of masses of volcanoes or large flood basalt provinces (LIP in image below). In the case of the worst mass extinction — the Permian — the Siberian flood basalts were thought to have injected magma into peat and coal formations which then injected a very large amount of carbon dioxide into the Earth’s atmosphere and oceans.

(In the Earth’s deep past, the worst global mass extinctions were driven by large igneous provinces like the eruptions across Siberia during the Permian. The initial killing mechanism during these extinctions was a result of the upshot ocean anoxia, acidification, and biochemistry change. During the Permian, effects eventually spilled over to land and possibly the upper atmosphere. Today’s human carbon emissions will ultimately produce worse impacts over shorter time scales than the Permian. Image source: Skeptical Science and The History of Seawater Carbonate Chemistry, Atmospheric CO2, and Ocean Acidification.)

Higher atmospheric and ocean carbon drove both environmental and geochemical changes — ultimately setting off hyperthermal temperature spikes and ocean anoxic events that were possibly assisted by methane hydrate releases and other climate and geophysical feedbacks. The net result of these events was major species die-offs in the ocean and, during the worst events, on land.

Considering the fact that present human activities, primarily through fossil fuel burning, are releasing vast quantities of carbon into the Earth’s atmosphere and oceans at a rate never before seen in the geological past, it appears that the world is racing toward another major mass extinction. In the past, the location of this dangerous precipice was a bit murky. But a recent study in Science Advances attempts to better define the threshold at which the worst of the worst mass extinction events — set off by rising ocean and atmospheric carbon — occur.

310 Billion Tons Carbon Entering Ocean = Mass Extinction Threshold

The study used a relatively easy to identify marker — ocean carbon uptake — in an attempt to identify a boundary limit at which such mass extinctions tend to occur. And the study found that when about 310 billion tons of carbon gets taken in by the oceans, a critical boundary is crossed and a global mass extinction event is likely to occur.

Presently, human beings are dumping carbon into the atmosphere at an extremely high rate of around 11 billion tons per year. Today, about 2.6 billion tons per year of this carbon ends up in the ocean. In total, since 1850, humans have added about 155 billion tons of carbon to the Earth’s oceans — leaving us with about another 155 billion tons before Rothman’s (the study author) extinction threshold is crossed.

(Thresholds of Catastrophe in the Earth System finds that present carbon emissions bring us about halfway to the global mass extinction boundary limit. That carbon emissions cuts need to be more aggressive than the most aggressive present international policy scenario to reliably avoid risk of setting off a global mass extinction event.)

At the presently high rate of fossil fuel burning and greenhouse gas emissions from humans, that gives us about 60 years. This is true even if emissions levels remain steady and do not increase. If emissions increase along a business as usual pathway, we could cross that threshold by or before the 2050s. And under all present emissions scenarios identified by international climate policy, the 310 billion ton threshold is either closely approached or greatly exceeded by 2100.

This should set off warning bells for global governments and climate policy advocates alike. What it means is that halting fossil fuel burning and transitioning to renewable energy needs to occur at rather swift rates — with annual global carbon emissions peaking within the next 1-10 years and then rapidly diminishing to zero — if we are to avoid a high risk of setting off another major global mass extinction. Of course, this does not mean that such a response will avoid harmful climate impacts — a number of which have already been locked in. Just that such a major response would be needed to avoid a high risk of setting off a catastrophic global mass extinction event equal to some of the worst in all of Earth’s deep history.

Rapid Movement Toward Terrible Long-Term Global Consequences

The study notes that past major extinctions like the Permian occurred on 10,000 to 100,000 year time-scales. And that during these events the changes inflicted upon the global environment by major carbon additions to the ocean and atmosphere occurred too swiftly for organisms to adapt. The pace of human carbon addition is presently faster than even during the Permian — the worst mass extinction event. So if this very large carbon spike were to continue it has the potential to set off impacts as bad, or worse than the Permian and over much shorter time horizons.

The study also notes that it takes about 10,000 years for the worst impacts of a mass extinction carbon spike to be fully realized. So hitting the 310 billion ton threshold by or before 2100 runs a high risk of consigning the world to many, many centuries of increasingly worsening climate impacts.

Links:

Thresholds of Catastrophe in the Earth System

History of Seawater Carbonate Chemistry, Atmospheric CO2, and Ocean Acidification

Today’s Climate Change is More Comparable to Earth’s Worst Mass Extinction

Heading Toward a Permian Future

Hat tip to Abel