You ask: Dinosaurs survived when carbon dioxide levels were extremely high. Why can’t humans?
“you askis a series of Earth Institute experts addressing readers’ questions about science and sustainability. A reader asked us this question: “How did plants and animals survive when carbon dioxide levels were as high as 6,000 parts per million about 200 million years ago?” Paul Olsongeologist and paleontologist at Columbia Climatic Institute Lamont-Doherty Earth Observatorytakes us through what scientists know about carbon dioxide levels.
Paul Olson is a geologist and paleontologist at the Lamont-Doherty Earth Observatory at the Columbia Climate Institute.Photo: Kevin Krajick/Columbia Climate School
Although no one measured atmospheric carbon dioxide concentrations millions of years ago, paleoclimatologists can reconstruct past temperatures and carbon dioxide levels using ice core, annual rings, coral, ancient pollenand sedimentary rockThese natural recorders of climate fluctuations can also reveal how various plants and animals thrived or died during different geological periods.
For example, when studying the age of dinosaurs, some researchers dissect leaves trapped in layers of sediment. “When carbon dioxide levels are low, small holes in the leaf epidermis are more common,” explains Olsen.
Scientists like Olson have repeatedly found that at several times in Earth’s history, organisms experienced much higher concentrations. carbon dioxide and a hotter average temperature than today. However, that doesn’t mean that if we continue to heat the planet by burning fossil fuels, everything will be fine.
“The problem today is not just rising global temperatures or rising carbon dioxide levels. The problem is the speed of change,” Olson explained. “For most of Earth’s history, carbon dioxide levels typically changed very slowly. This gave organisms and their ecosystems ample time to adapt to climate change through evolution and migration.”
climate scientist warn Over the next century, the rate of change will be 10 times faster than any climate pattern seen in the past 65 million years. As a result of today’s rapid warming, up to 14 percent of land-based flora and fauna could face extinction in the coming decades. Report From the Intergovernmental Panel on Climate Change.
Earth’s climate fluctuations
During the Cambrian period from 542 million years to 485.4 million years ago, some sources estimate that carbon dioxide levels may have been around 20 times higher than today, the temperature 10 degrees Celsius increase in temperature.
Creatures don’t seem to mind a hot environment. During this period, the oxidation of the oceans led to an explosion of life known as the “Cambrian Explosion.”There are a variety of marine life, such as trilobites, including abnormal, and slug-shaped shellfish.Meanwhile, on land, the earliest plants began to take root and sprout 500 million years agolikely enjoying high levels of atmospheric carbon dioxide, said Olson.
“But the proxies of 500 to 400 million years ago weren’t that good at this time,” he warned. “Most data and graphs of carbon dioxide levels in Earth’s history start around 350 million years ago.”
Reconstruction of carbon dioxide levels over the past 400 million years or so. Blue areas represent ice ages. The graph shows that several mass extinction events occurred at the same time as rapid changes in carbon dioxide levels.Source: Foster et al., 2017, modified by Paul Olsen
During this period Ordovician (approximately 488.3 to 443.8 million years ago), sea level was 220 meters higher than it is today; areas north of the tropics were under the ocean. raw fish, Red algaecorals and some other marine animals, such as cephalopods and gastropods, were part of a thriving ecosystem – until they suffered an unprecedented tragedy, possibly triggered by sudden changes in carbon dioxide levels.
It was the first mass extinction on Earth.It wiped out about 85% of marine species starting about 443 million years ago up to two million yearsThe reason is unclear, but some scientists speculate that it may be related to the formation of massive glaciers and a dramatic drop in sea levels after the Gondwana supercontinent drifted toward the Antarctic.One 2012 Research suggest that the first terrestrial plants may have caused the ice age by absorbing carbon dioxide and causing the global temperature to plummet.Instead, in a Study in 2020Canadian scientists have hypothesized that widespread volcanic eruptions released massive amounts of carbon dioxide, which suddenly warmed the planet and triggered two mass extinction pulses within 2 million years.
How did dinosaurs survive despite unusually high levels of carbon dioxide?
The Triassic period (25.2 to 201 million years ago) ushered in the age of dinosaurs.
“It was very hot at the time because the concentration of carbon dioxide in the atmosphere was five times higher than today’s levels,” Olson explained. “However, marine and terrestrial life is thriving.”
At the beginning of the Triassic, the Pangaea supercontinent covered the landmass of all seven modern continents. Mammal-like reptiles or synaptic animals dominated the world. frog and salamander It has only just begun to evolve. After that, the wider archosaur — a group of reptiles that includes crocodiles, birds and dinosaurs — took over.
The first dinosaurs appeared about 232 million years ago. They are as small as dogs.
For the Late Triassic and Early Jurassic (roughly 237 to 174 million years ago), scientists have found zero evidence in the fossil record for polar glacial ice sheets — which could be carbon dioxide levels as high as 6,000 parts per million result. In this greenhouse state, dense coniferous and deciduous forests cover much of Pangaea, from the Arctic and Antarctic to subtropical latitudes.
However, about 230 million years ago, Pangea began to break up. When North America drifted away from Eurasia and Africa, magma invaded a large area of the Earth’s crust, causing one of the most important volcanic eruptions in Earth’s history. It triggered a mass extinction event 202 million years ago that wiped out 80 percent of life, including many of the previously dominant Triassic large tropical reptiles, such as crocodile-like phytosauruses.
Most researchers believe that the mass extinction event at the end of the Triassic was directly related to widespread volcanic eruptions, Olson said. Each eruption can last for decades or even centuries, and there are many eruptions. They are associated with a sudden doubling to tripling of atmospheric carbon dioxide over a short period of time.
“This is comparable to what humans are doing to Earth right now,” he said. A 2019 study showed that human activity releases as much as 100 times more carbon content In the atmosphere than volcanoes.
Unusually high carbon dioxide levels 202 million years ago led to ocean acidification and hypoxia, or loss of oxygen underwater. Olson and his colleagues identified these factors as the biggest drivers of the mass extinction event that wiped out marine invertebrates and corals.
in a A recent study, they found that large amounts of sulfur dioxide were also pumped into the atmosphere during the various pulses of volcanic eruptions. This led to intense but brief periods of cold as sulfur aerosols reflected sunlight into outer space.
“That cold period probably only lasted a few years or at most 100 years,” Olson explained. On land, volcanic winters wipe out animals without insulating materials such as feathers, fat or thick layers of fur.Dinosaurs with enough insulation survive and take over.
After each brief cold period, Earth has experienced tens to hundreds of thousands of years of global warming due to a sudden increase in carbon dioxide levels in the atmosphere caused by volcanic eruptions.
How did global temperatures and carbon dioxide levels stabilize before people came along?
Extremely high concentrations of carbon dioxide disappear from the atmosphere through three main mechanisms. The first is that the oceans absorb large amounts of it to create an equilibrium in the atmosphere.
The second mechanism by which Earth absorbs carbon dioxide from the air is through the weathering of rocks. The product of this natural carbon sequestration ends up in the ocean as limestone.
The third mechanism is photosynthesis. Plants absorb carbon dioxide, and if they are buried in sediments before they decompose, the carbon in their tissues is stored underground. These three mechanisms occur slowly over thousands of years.
“But when Earth experiences rapid changes in atmospheric carbon dioxide concentrations — as we experience today due to human activity — these three mechanisms don’t react fast enough to compensate for the staggering rates of change,” Olson explained.
Over the past 60 years, the annual growth rate of CO2 in the atmosphere has been 100 times faster Relatively newer natural growth than occurred at the end of the last ice age, about 17,000 years ago. In 2021, the average global concentration of carbon dioxide will reach the highest level on record 414.72ppm.
“This is similar to the rate of change that occurred about 202 million years ago, after a huge volcanic eruption, and after the asteroid impact that triggered the fifth mass extinction event about 66 million years ago,” Olson added.
Can humans survive in harsh climates like the age of dinosaurs?
Carbon dioxide levels today are higher than those of the past 800,000 years. picture: NASA
Although carbon dioxide levels on Earth have fluctuated countless times in the past, most of them have fluctuated at a rate that organisms can adapt and evolve to adapt to climate change. In today’s rapidly warming environment, that’s unlikely to happen.
“The rate of change we are experiencing today is the highest the planet has ever seen, due to human-driven greenhouse gas emissions,” Olson said. “Higher levels of carbon dioxide in the atmosphere are the normal state of our planet. Our current lower state is unusual. What matters, however, is the speed of this change.”
Olson hypothesized that it was possible for humans to survive even when atmospheric carbon dioxide levels as high as 6,000 ppm were recorded during the age of the dinosaurs and subsequent global warming—thanks to technological progress, not evolution.
Even if the inner regions of the continents would be unbearably hot, high latitudes might still be cool and habitable.
However, with high rates of climate change in the short term, Olson warns that societies will be severely disrupted due to limited food and water resources, leading to wars and conflicts.
In other words, our species can theoretically survive, but we may not live our best lives.
