The climate on Earth is always changing. Usually, this happens gradually, with temperature changes of tenths of a degree over millions of years, allowing ecosystems time to adapt. However, there are periods in Earths history when the climate changed abruptly, with drastic consequences. One of the best-known examples is the Paleocene-Eocene Thermal Maximum (PETM). Can we use this period as a (possibly concerning) lesson for todays climate change? The answer is yes - but with a crucial difference: it is happening many times faster now.
The PETM: Exceptionally Rapid Warming
At the boundary between the Paleocene and the Eocene, about 56 million years ago (9 million years after the extinction of the dinosaurs), a strong warming of the Earth occurred (see image 1). There is evidence that small changes in the Earths orbit triggered the PETM (known as astronomical forcing). Scientists estimate that 3000 to 10,000 billion tons of carbon entered the oceans and atmosphere, primarily in the form of methane. Methane is broken down into CO2 over a timescale of about ten years. There are several theories about the cause of this release, including the release of methane from the seabed due to an underwater landslide and extreme volcanic activity in the Atlantic Ocean. Whatever the cause, the effects were felt worldwide. Due to this carbon pulse, the Earth warmed by 4 to 8 degrees within 10,000 years. A rate that is exceptionally fast by geological standards. Such rapid periods of warming are also referred to as hyperthermals.
Consequences for Ocean and Land
The increased CO2 in the oceans led to acidification, resulting in the extinction of about 40 percent of benthic foraminifera (calcareous, single-celled deep-sea organisms). The number of coral reefs also significantly decreased. Many species migrated: tropical plants and animals sought refuge at higher latitudes. Others had time to adapt to the new climate. An example of this is that particularly hoofed animals showed dwarfism: the shrinking of a species as an evolutionary response to heat stress and the decrease of nutrients in plants. The PETM is therefore seen as an important driver of evolution and migration during the Paleogene. Although the PETM did not cause a mass extinction, ecosystems have permanently changed since the PETM, and many deep-sea organisms have gone extinct.