February 27, 2012

Darwin Day Lecture: “Adaption and Extinction in the Wake of Climate Change”

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Climate changes are nothing new to the Earth, but scientists now predict that the Earth, as we know it, may transform much sooner than we thought.  Cornell faculty members spoke on a panel discussion, “Adaptation and Extinction in the Wake of Climate Change,” on Feb. 13 that marked the second event of the weeklong Darwin Days series.  Dr. Warren Allmon, Dr. Charles Greene, and Dr. Drew Harvell discussed the implications of climate change as it pertained to their respective fields.  Prof. Allmon, earth and atmospheric sciences, said that, up until the last 10,000 years, climate fluctuations were far more intense relative to recent changes.  The Earth is divided into two large climatic categories: the Icehouse and the Greenhouse.

Greenhouse periods were times when the Earth had little or no ice on it and temperatures were significantly warmer, while Icehouse periods were times marked by glaciers and lower temperatures.  Time on Earth is currently in the Icehouse state, but there is concern that a transition into another Greenhouse period is in the near future, he said.  “The real risk is that runaway greenhouse effects will eventually kick us out of an icehouse climate regime,” Allmon said.

Prof. Harvell, ecology and evolutionary biology, draws upon climate change’s immediate impact and supports Allmon’s concerns for the future. Coral reefs are home to 20% of all fish and represent the most biodiverse marine ecosystem in the world.  Coral symbionts, called zooxanthellae, are photosynthetic algae that reside within coral tissues and provide them with valuable nutrients. When water temperature rises, the zooxanthellae are stressed and subsequently expelled from the coral.  Left without their source of nutrients, corals lose their pigment in a process known as “coral bleaching.”  Without the successful function of coral symbionts, coral life is directly threatened. Rising levels of carbon dioxide in the atmosphere largely exacerbate the impact of temperature increases on corals and their symbionts. Human made carbon dioxide, derived from the burning of fossil fuels, significantly contributes to the recent escalation in atmospheric carbon dioxide.  Carbon dioxide in the atmosphere poses a threat to corals and other marine life because water absorbs carbon dioxide and converts the compound into carbonic acid, a chemical that is toxic to corals in excess amounts.  Between thermal stress and climbing carbon dioxide levels. “We expect to pass a threshold where the ecosystem is no longer resilient and finally where there can’t be physiological function for corals,” Harvell said. Prof. Greene, earth and atmospheric sciences, highlighted occurring changes in the arctic and the effect of those changes on both neighboring and distant regions. One of Greene’s computerized animations illustrated the earth’s rising temperatures since 1900.  Since the Industrial Revolution, warming of the earth has taken off at a much more rapid pace than before.  Temperature increases, he stressed, are not a uniform phenomenon, but certain regions, such as the arctic, are likely to warm at a faster pace. Arctic ice melting leads to an inflow of cold water into the mid-Atlantic, which directly impacts marine species.  While cod were once the most successfully sold fish in Canada, the decrease in water temperatures has contributed toward the declining numbers of cod stock in the Atlantic. Snow crab and shrimp, both cold water species, are now the most successful in fish markets, he said. The changes in the arctic, although they may occur thousands of miles away, even have industrial repercussions. In a time when many thresholds are being crossed, Allmon noted, environmental scientists studying both large and small temporal scales have found tremendous overlap in their work. He stressed that “we could change the history for the world for the next hundreds of millions of years in the next century.  There is no withdrawal once we hit those tipping points.”

Original Author: Caitlin Parker