From: Reuters
Published February 12, 2008 09:46 AM

Insects ravaged more plants in ancient hot period

By Deborah Zabarenko, Environment Correspondent

WASHINGTON (Reuters) - Insects ate more plants, and did more kinds of damage to them, during an ancient hot period that offers hints of what might happen this century if global warming forecasts hold true, scientists reported on Monday.

Earth warmed by about 9 degrees Fahrenheit over the course of 5,000 years at the end of the Paleocene Era, some 55 million years ago, sending hordes of hungry insects from the tropics and subtropics into the temperate zone, where the climate was suddenly warm enough for them to survive.

This temperature change is an eyeblink in terms of geologic time, but far less abrupt than the warming predicted for the 21st century by the U.N. Intergovernmental Panel on Climate Change, which forecast Earth could heat up by 3.2 to 7.2 degrees F (1.8 to 4 C) by the year 2100.


The ancient heat spike -- known as the Paleocene-Eocene Thermal Maximum -- started with a quick rise in temperature over about 5,000 years, and then the planet stayed warm for about 100,000 years before cooling back down, according to study author Ellen Currano of Pennsylvania State University and the Smithsonian Institution.

At the same time, the amount of carbon dioxide in the atmosphere tripled, making plants less nutritious and forcing insects to eat more to sustain themselves, Currano and other researchers reported in the Proceedings of the National Academy of Sciences.


"As far as insect feeding goes, during this time the number of types of damage is higher and also we see almost a doubling in the frequency of leaves being damaged," said Currano said in a telephone interview.

To discover this, Currano and other researchers looked at plant fossils from the badlands of Wyoming dating from before and after the big warm-up. They discovered that not only did the insects eat more, but they did more varied kinds of damage to the plants they attacked.

The insects mined the leaves, ate what they could on the surface and laid eggs inside the leaves, causing a reaction known as galling, in which the plant grows a kind of tumor on which the young insect feeds.

Because they looked at fossils ranging over about 4 million years, the scientists got a long-term look at the impact of climate change, Currano said.

"What we think we've seen is that insects from the tropics and subtropics have moved northward as it gets warmer," she said, adding that the increased carbon dioxide -- which occurred naturally 55 million years ago but which is increasing now due to the burning of fossil fuels -- probably spurred the increased plant damage.

"We might also expect that as carbon dioxide levels rise, we would see this increase in (insect) feeding that we see in the Paleocene-Ecocene Thermal Maximum," Currano said.

Why carbon dioxide increased long ago is a matter of scientific debate, with some theorizing that massive fires or volcanic eruptions might have caused it.

(Editing by Eric Walsh)

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