Would life adapt to a warmer climate?
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In Brief: Events in Earth’s past when fossilized carbon was rapidly released into the atmosphere are characterized by extinctions and life-limiting acidic ocean waters.
Many forms of life are tremendously adaptable, but how easily they adapt depends largely upon the rate of change. A car going from 60 miles per hour (mph) to zero mph over the course of a gradual 30-second deceleration has far different consequences for its passengers than a car going from 60 to zero in just a second or two. Similarly, neither warm nor cold conditions are necessarily detrimental to life on Earth, but sudden shifts between these conditions are. Gradual changes in Earth’s carbon dioxide (CO2) concentrations and temperature, like the cooling that occurred from about 50 to 1.8 million years ago, have far different consequences for life on Earth than a sudden cooling of similar magnitude, such as the one that occurred over as little as a few days after the asteroid impact 65 million years ago that led to the extinction of the dinosaurs. During the gradual cooling, life flourished and achieved new levels of diversity and ecosystem complexity. Following the rapid cooling 65 million years ago, many species died.
Rapid periods of warming have also resulted in mass extinctions, such as the extinctions at the end of the Permian period at around 250 million years ago. 1-2 gigatonnes (1-2 billion metric tonnes, or about 3.3 trillion pounds) of carbon were released each year over a period of about 50,000 years during this event. The Paleocene-Eocene Thermal Maximum (PETM), which happened around 55.8 million years ago, was a similar event that occurred over a shorter period of time. The estimates for the most rapid addition of carbon to the atmosphere during the PETM fall at around 2.2 gigatonnes a year. By contrast, humans put about around 6.5 gigatonnes of carbon in the atmosphere each year today, a number that continues to climb. Both the Permian and PETM events were likely triggered by shifts in plate movements causing carbon and sulfur-rich rocks to come into contact with magma, releasing lots of carbon and sulfur dioxide molecules into the atmosphere. This Permian mass extinction was likely the worst extinction event Earth has ever faced, with more than 90 percent of animal species disappearing from the geologic record. The PETM featured the rapid movement of mammals from the tropics into the higher latitudes, as well as severe impacts on ocean microorganisms.
While most discussion of the impacts of carbon emissions focuses on how they are changing or could change the weather, probably the most dramatic consequences of sudden CO2 additions to the atmosphere happen when this CO2 is absorbed by the ocean. Such spikes change the chemistry of ocean waters, making them far less habitable and leading to poorer ecosystems. This is evident from the geologic record, which shows that sudden jumps in CO2 concentrations – due to periods of volcanic activity or collisions with asteroids – feature major changes in the chemistry of seawater. These changes were accompanied by large drops in the total number of organisms living in the oceans and extinctions of many species. The images below illustrate the impact the rapid releases, but not as rapid as today’s releases, during the PETM had on cocolithopores, tiny organisms that provide food for the rest of the food chain.
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(Images: A microscopic view of ocean sediment cores laid down before (top) and after (bottom) sudden releases of carbon dioxide during the Paleocene-Eocene Thermal Maximum 55.8 million years ago. The “sudden” release of CO2 caused acidification of the oceans and the dissolution of the cocolithopores that are a major component of the ocean food web. It also caused major extinctions in the ocean. Images Courtesy of Brian Huber, Smithsonian Institution) |
Sources:
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