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Scientists at San Diego State are researching an ancient global warming event in hopes of providing information that can help accurately predict modern global warming changes.
Stephen Schellenberg, Ph.D., a professor in the geological sciences department, and the students in his lab are researching previous global warming events to get an idea of how the planet has responded in the past. He's researching an intense warming event that occurred 55 million years ago, known as the Paleocene-Eocene Thermal Maximum.
During this event, massive amounts of carbon and other greenhouse gases were released into the atmosphere, causing a rapid increase in global temperature. This increase occurred during the course of thousands of years, and the Earth's climate took tens of thousands of years to recover from the influx of greenhouse gasses.
The information obtained from these experiments about the Earth's climactic history is used to assess how the Earth responds to the influxes of greenhouse gasses. Schellenberg and his team are looking at the PETM event carefully because it is similar to present-day global warming. Both the PETM and today's global warming represent events where massive amounts of greenhouse gases are poured into the atmosphere in a short amount of time.
"The PETM represents the best analog in terms of rate, and still, it took thousands of years, and we'll probably reach the same amount of carbon in hundreds of years," Schellenberg said.
Schellenberg and one of his graduate students, Elizabeth Landau, are trying to discover more about this event by analyzing fossils recovered from the Ocean Drilling Program, a research cruise that travels the world gathering samples from the seafloor.
Landau's research on the PETM is based on these samples as well as other samples that come from an international archive of sediment cores. She is looking specifically at how organisms called Ostracodes were affected before, during and after the PETM, giving insight to how living organisms changed with respect to their environment.
Their research method is two-fold; after obtaining the samples, the tedious process of separating the individual organisms by species from the sediment occurs, and the bodies of the Ostracodes are analyzed by hand. The scientists are looking for evidence of a poor living environment. Then, a chemical analysis will be done.
Because the ocean acts like a sponge and absorbs a large portion of what is in the air, the chemistry of the ocean changes. By adding greenhouse gases such as carbon, the ocean becomes more acidic, making survival for any living organism much more difficult.
Under the microscope, it's clear that there was degeneration in the Ostracode bodies throughout the PETM. The difficult living environment forced some species to have less robust body physiologies and sent others into extinction.
"We can create a baseline of temperature changes based on who's thriving and who's not and by comparing them to modern species," Landau said.
The surviving PETM Ostracode species present today have been used to determine the ancient temperatures throughout the PETM, chronicling the changes. The current estimation of the temperature change was about 5 to 7 degrees (Celsius).
The final stage in Landau's graduate research with Schellenberg will be a chemical analysis to determine what PETM-age Ostracodes are made of. Some atoms, although they may have the same names, come in different varieties, such as Carbon-14. This is used to determine the age of ancient artifacts, although the majority of this element is Carbon-12. These atoms are called isotopes and are distinguished by varying weights. When the temperature of the Earth changes, the isotope used in the organism's body changes as well.
The results of this final stage are pending, but based on the overwhelming amount of paleoclimate isotope data, it is unlikely that her research would be inconsistent with past results.
Schellenberg is providing detailed pieces of information that describe what happened to the Earth in the past. To better understand the current global warming trends on Earth today, it is imperative to thoroughly assess how the Earth responded to a similar event in the past. By studying organisms' responses to their environment, Schellenberg and his lab can create a timeline of when major changes in Earth's temperature, oceans and ocean circulation patterns occurred and how long it took for Earth to recover. All the climate models in use today take this paleoclimate data into account.
Ultimately, one lesson that can be taken away from the PETM is that the Earth is resilient and it recovered from all the greenhouses gases emitted into the atmosphere, but that took a long time.
"Eventually, the Earth will reach a stable point," Landau said. "It might not be a place where we can live or where animals can live, but it will recover."
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