Global warming shook Earth 300m years ago

Global warming, biodiversity loss and climate change are rapidly growing concerns across the world – but scientists claim they already hit Earth 304 million years ago.

The study has found that during this time the planet had ice caps and glaciers comparable to today and that carbon dioxide in the atmosphere doubled, oceans lost oxygen and biodiversity dropped considerably on land and at sea.

Lead author Isabel Montañez, from the University of California Davis, describes it as “one of the fastest warming events in Earth’s history”.

Her team of researchers investigated the period spanning form 300 million to 260 million years ago, finding that during this time Earth’s climate fluctuated back and forth many times between a glacial icehouse to a hot greenhouse.

Looking into carbon isotopes from rocks and plant fossils 304 million years ago, they were able to uncover the atmospheric carbon dioxide levels the Earth would have been experiencing at the time.

This period is called the Kasimovian–Gzhelian boundary or KGB – and the scientists found that 9,000 gigatonnes of carbon were released into the atmosphere just before this event took place.

This doubled the amount of carbon in the air if compared to modern levels before the industrial revolution.

Using the findings of the study, the authors have explained that an understanding can be made of what it could mean for life on Earth if emissions are not curbed.

For instance, the melting of the ice caps released fresh water onto the ocean surface, which creates a barrier for oxygen reaching the deep levels of the ocean – causing deeper marine life to die.

Studying rocks from the bottom of the ocean at the time, they estimate that 23% of the seafloor worldwide became anoxic dead zones – which is where they are starved of oxygen.

They believe that volcanic activity is what led to heavy temperature and carbon rises – but this is worsened by human activity in a modern world.

“If you raised carbon dioxide by the same amount in a greenhouse world, there isn’t much effect – but icehouses seem to be much more sensitive to change and marine anoxia,” Montañez explained.

Our modern world falls into the latter category of an ice-capped planet, so the scientists project that the amount of organic carbon released from melting caps will only cause more of an oxygen block to life.

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