End-Permian Hyperthermal Event (~252 Million Years Ago)

This event predates the age of dinosaurs and was marked by a global temperature rise of 6–11°C, resulting from significant CO2 emissions linked to volcanic activity in present-day Siberia. This period also saw increased ocean acidification and low oxygen levels in marine environments.

The consequences were severe, leading to Earth's most significant extinction event. Estimates suggest that 81% of marine species (like corals and fish) and 70% of terrestrial species (including early mammal ancestors) disappeared. To illustrate, envision a child's animal encyclopedia with 75% of its content removed.

End-Triassic Hyperthermal Event (~201 Million Years Ago)

At this juncture, dinosaurs were beginning to thrive on Earth, just before the Jurassic Period. Similar to the End-Permian event, volcanic eruptions played a crucial role.

These eruptions released significant quantities of CO2 and sulfur dioxide, causing a global temperature increase of +6°C. Rising sea levels and ocean acidification followed.

Researchers measured gas bubbles trapped in ancient volcanic rocks to quantify the CO2 released, discovering it was comparable to current greenhouse gas emissions.

The results were dire, with approximately three-quarters of all species going extinct, including all Triassic archosaurs, except for dinosaurs, pterosaurs, and crocodiles. Marine life suffered the most.

Toarcian Oceanic Anoxic Event (~183 Million Years Ago)

By this time, dinosaurs roamed the land, while plesiosaurs and ichthyosaurs swam in the oceans. Once again, massive volcanic activity, likely triggered by a disturbance in the global carbon cycle, caused significant sea level rise and increased seawater temperatures.

This led to a dramatic surge in marine primary productivity, resulting in rampant algal growth. When these algae died, they sank to the ocean floor, escalating methane emissions and exacerbating global warming and rising sea levels. This process also contributed to crude oil formation.

Crude oil consists of hydrocarbons formed from the decay of carbon-based organisms in ancient seas, subjected to high pressure and temperature for millions of years. — US Department of Energy

As temperatures rose, melting permafrost released even more methane, pushing temperatures up by +5°C.

This period culminated in a mass extinction event that was catastrophic for corals, with approximately 49% of coral genera wiped out.

Cretaceous Oceanic Anoxic Event 1a (~120 Million Years Ago)

The Cretaceous period represented the zenith of dinosaur dominance, with species such as Triceratops and T-rex. Evidence indicates that the Cretaceous Oceanic Anoxic Event 1a was driven by intense volcanic activity, releasing substantial CO2 into the atmosphere and resulting in a +4°C rise in global temperatures. This warming had extensive repercussions for ocean ecosystems.

A major consequence was widespread oceanic anoxia, where warmer waters lost their ability to hold oxygen, causing significant stress for marine life. This oxygen shortage led to mass extinctions among various species, including plankton and marine reptiles.

Cretaceous Oceanic Anoxic Event 2a (~94 Million Years Ago)

During this period, still within the age of dinosaurs, research suggests this event arose from a combination of factors, with volcanic eruptions being pivotal. These eruptions released vast amounts of CO2, resulting in a +4°C temperature rise, which affected ocean circulation and reduced seawater oxygen levels.

The consequences were profound, particularly for marine ecosystems. The lack of oxygen in large areas of the oceans disrupted nutrient cycling and altered the oceans' chemistry, leading to significant extinctions among marine species.

The Paleocene-Eocene Thermal Maximum (PETM) (~56 Million Years Ago)

This event occurred during the age of mammals, a particularly exciting time for paleontologists studying fossils from this era.

While the precise cause of the PETM remains unclear, there is a scientific consensus that rapid greenhouse gas releases, likely from volcanic activity and methane hydrates on the ocean floor, were significant contributors. The surge in greenhouse gases, especially CO2 and methane, resulted in a pronounced greenhouse effect, causing global temperatures to spike by +5°C.

This rapid temperature rise led to widespread ecological transformations, including shifts in ocean currents and sea level changes.

Marine life was especially impacted, with mass extinctions among foraminifera and other crucial marine organisms. Terrestrial ecosystems also underwent significant changes, including shifts in vegetation.

The PETM is marked by a distinctive geological layer known as the "clay layer" or "boundary clay," which serves as an indicator of this critical climatic event.

Then and Now

As illustrated, climate change has occurred throughout history, but these events were not random; they were driven by substantial greenhouse gas emissions.

While there are still active volcanoes today, they pale in comparison to the massive eruptions of the past, which released enormous amounts of toxic gases over vast areas. The End-Permian vulcanism, for instance, resulted in a sixfold increase in atmospheric CO2.

Geologists estimate that during the End-Triassic eruptions, approximately 100,000 km³ of lava was expelled every 500 years, matching the expected emissions from all human activities in the 21st century.

If we wish to learn from history, we must acknowledge that the cascading effects of rising greenhouse gases could be disastrous for modern ecosystems. The increase in temperatures is just the beginning, with changes to ocean circulation, ocean acidification, and potential anoxic events on the horizon.

Some may argue that they are indifferent to the fate of ecosystems, believing it won’t impact us. However, we are intrinsically part of these ecosystems. Changes in rainfall patterns will affect crop yields, and the extinction of species will have repercussions for food production and water resources.

We can only begin to comprehend the potential consequences of a seemingly "small" increase in global temperatures on our planet. Fortunately, studying the fossil record allows us to view the past as a vast experiment. Understanding our history will enable us to better grasp the present and make informed predictions about the future.