Dinosaurs survived when CO2 was extremely high. Why can’t humans?

Current rates of temperature increase, if accurate, don’t look all that startling despite the odd few hot days. For example, Roy Spencer reports a linear warming trend of +0.13C per decade since 1979. We know previous cooling trends must have occurred over the centuries from the regular advance and retreat of glaciers, to cite one obvious line of evidence. Focussing on CO2 all the time is a bit like looking through the wrong end of the telescope.
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How did plants and animals survive around 200 million years ago when the carbon dioxide concentration went up to 6,000 parts per million?

Paul Olsen, a geologist and paleontologist at Columbia Climate School’s Lamont-Doherty Earth Observatory, walked us through what scientists know about carbon dioxide levels over time, says Phys.org.

Although no one was around to measure the atmosphere’s CO2 concentration millions of years ago, paleoclimatologists can reconstruct past temperature and carbon dioxide levels using ice cores, tree rings, corals, ancient pollen, and sedimentary rocks.

These natural recorders of climate fluctuations can also reveal how various animals and plants thrived or perished during different geological periods.

While studying the Age of Dinosaurs, for example, some researchers dissect leaves that got trapped in sediment layers. “The little holes in the skin of leaves are more common when there are lower carbon dioxide levels,” explained Paul Olsen, a geologist and paleontologist at Columbia Climate School’s Lamont-Doherty Earth Observatory.

Scientists like Olsen have repeatedly found that during several periods of Earth’s history, organisms have experienced radically higher concentrations of carbon dioxide and hotter average temperatures than today. However, that doesn’t mean everything will be fine if we keep heating the planet by burning fossil fuels.

“The problem today is not higher global temperature or carbon dioxide levels alone. The problem is the rate of change,” explained Olsen. “Throughout most of the Earth’s history, carbon dioxide levels have generally changed very slowly. That gave organisms and their ecosystems sufficient time to adapt to climate change through both evolution and migration.”

Climate scientists warn that over the next century, the rate of change will be 10 times faster than any climate pattern that unfolded in the last 65 million years.

Because of today’s rapid rate of warming, up to 14 percent of all plants and animals on land may face extinction in the coming decades, according to a report from the Intergovernmental Panel on Climate Change.

Earth’s climatic ups and downs

During the Cambrian Period, which lasted from 542 million to 485.4 million years ago, some sources estimate that CO2 levels may have been about 20 times higher than today, and temperatures were hotter by 10 degrees Celsius.

Living things didn’t seem to mind the scorching conditions. During this time, the oxygenation of the oceans led to a burst of life known as the “Cambrian explosion.” There was a diverse range of marine creatures like trilobites, including larger ancient predators called Anomalocaris, and slug-shaped animals with shells.

Meanwhile, on land, the earliest plants started taking root around 500 million years ago, possibly enjoying high levels of atmospheric carbon dioxide, said Olsen.

“But the proxies from 500 to 400 million years ago are not that well worked out at this time,” he cautioned. “Most of the data and graphs of carbon dioxide levels in the Earth’s history start at around 350 million years ago.”

During the Ordovician Period (around 488.3 to 443.8 million years ago), the sea level was as much as 220 meters higher than today; the regions north of the tropical belt were under the ocean. Primitive fish, red algae, corals, and a few other marine animals like cephalopods and gastropods were a part of thriving ecosystems—until they were struck by an unprecedented tragedy, which may have been triggered by sudden changes in CO2 levels.

It was Earth’s first major mass extinction. Beginning about 443 million years ago, it wiped out approximately 85 percent of all marine species for up to two million years. The cause remains unknown, but some scientists speculate that it might have been associated with the formation of massive glaciers and a drastic drop in sea levels after the super-continent Gondwana drifted towards the South Pole.

A 2012 study suggested that the first land plants might have caused global temperatures to plummet by absorbing CO2, triggering an ice age.

Conversely, in a 2020 study, Canada-based scientists hypothesized that widespread volcanic eruptions released huge amounts of carbon dioxide that abruptly heated the planet and set off two pulses of mass extinctions within two million years.

Full article here.