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By Kelly

Here in the Southern Hemisphere it’s time to head to the BBQ because it’s getting warmer. I’m not talking about the effects of climate change I am merely referring to the seasonal cycle. But seeing I brought it up, let’s talk a little about temperature… For something different though let’s talk about temperature during a different period in Earth’s history. Climate scientists like to look at all sorts of climate anomalies through the Earth’s history as it gives us an idea of how Earth, and all its inhabitants, may respond to current perturbation. For example, as we hurtle toward a greenhouse state with oceans that are not only warmer and more acidic, but are also predicted to have less oxygen in them (sounds delightful), how can we begin to understand how marine biota will respond?

To spoil the punchline a little, some 250 million years ago the Earth was in a greenhouse state similar to the one we are hell-bent on revisiting, and it had catastrophic effects on marine life. And this is not hyperbole, it took 5 million years for life to recover to its former extent. But is it sensible to draw analogies with such a distant time?

A similar extinction event occurred 55 million years ago, known as the PETM or Paleocene-Eocene Thermal Maximum, and is often quoted as being analogous to our current warming scenario. This new research by Sun et al., (published in October in Science) argues that the PETM doesn’t capture the severity of change required to mimic our present predicament. For that we need to go to the end-Permian Mass Exticntion event where igneous provinces erupted through coal and similarly organic rich deposits injecting gases into the atmosphere that created a greenhouse state (sound familiar?)

If you are intending on hiding your head in the sand in relation to the current climate crisis, wondering how bad can it really get, the authors of this recent paper can give you an idea. The early Triassic oceans are thought to have been almost 40C at the equator, that’s 10-15 degrees warmer than present day averages. Back then low oxygen waters were not just isolated to the deep-sea, they extended in some regions to the surface, where sulfidic environments prevailed as evidenced by the abundance of green-sulfur bacteria. Ocean acidification events also occurred further limiting the growth of reef building coral. However the authors argue that habitat restriction for corals, marine reptiles, bryozoa and calcareous algae was amplified by acidification events, but ultimately forced by temperature.

Now where this analogy falls apart is that the Earth really was a different world back then, as in the continents were arranged very differently in a Pangea-like state and therefore circulation patterns were VERY different. However, while we can all agree that further work is needed that takes these caveats into account, the toasty triassic was indeed a microbial world, and that doesn’t bode well for the human species who have gone from commiting to 2-4C warming, to possibly 4-6C, in the space of a decade.

As we prepare for the christmas season here in the southern hemisphere, a time when many of us flock to the beach, spare a thought for unbridled climate change, and having the next 5 million new year’s eve BBQs on the shores of a hot, anoxic, sulfidic sea…shrimp anyone?

For the full article you will need a subscription to Science where you can see the full article here.