Recent studies of some of nature's environmental "records" show that global warming can penetrate deep into the ocean faster than scientists have realized. In fact, some such penetration may have already begun.
The record keepers are foraminifera - "forams" for short - creatures so tiny that several could sit together on a pinhead. The mineral composition of their shells reflects the environmental conditions under which they grow. Flavia Nunes and Richard Norris at the Scripps Institution of Oceanography in La Jolla, Calif., reported earlier this month in Nature that the foram record includes a global warming event that provides a warning for our own times. Although it occurred 55 million years ago, they consider it a good analogue for studying the causes and consequences of our own global warming.
Geophysicists call the event the Paleocene/Eocene Thermal Maximum. Several degrees of global warming caused major changes in global ocean circulation patterns. This, in turn, brought warm water into normally frigid deep sea depths. It was accompanied by mass extinctions of bottom-dwelling marine life, according to the fossil record. This massive climate change happened in less than 5,000 years. However, Drs. Nunes and Norris point out that it may have happened even more quickly.
Commenting on this in the Scripps announcement, Nunes said that the key finding is that "the Earth is a system that can change very rapidly." The climate change involved a substantial rise in greenhouse gases such as carbon dioxide and methane. Although there was no human input, this is another example of the important role such gases play in climate change.
There does seem to have been a massive release of methane from the sea bed when warming thawed out frozen methane reservoirs there. This is a hazard in our own time.
"What this tells us is that the changes that we make to the Earth today (such as anthropogenic induced global warming) could lead to dramatic changes to our planet," Nunes explained.
Meanwhile, David Field, another Scripps researcher who has been working with several Mexican and US colleagues, has found evidence that global warming is beginning to penetrate the ocean today. Dr. Field, now at the Monterey Bay Aquarium Research Institute, and his co-researchers described that warming earlier this month in Science.
They looked at foram records off southern California for the past 1,400 years. Those records show considerable climate variations, decade by decade. Nevertheless, the 20th century stands out. Its later years brought what they call indications of "a deep, penetrative warming not observed in previous centuries." They document extensive changes in small animal and plant species with cold-loving forms giving way to warmer-water types. "These results imply that 20th-century warming, apparently anthropogenic, has already affected lower trophic [nutritional] levels of the California Current," they report.
Scientists concerned about man-made climate change have repeatedly warned about the possibility that the buildup of CO2 and other greenhouse gases driving global warming may push natural systems over a threshold where change exceeds their natural range of variability.
In the announcement of his group's findings, Dr. Field said that "changes since the 1970s have been particularly unusual and show that ocean ecosystems in the northeastern Pacific have passed some threshold of natural variability."