Ancient Climates, Future Challenges: Lessons from the Geologic Record

Ellen M. Bishop
Oregon Paleo Lands Institute, Fossil, OR

The accelerating recognition of climate change marks the rise of a new paradigm and new priorities for the 21st century. The record is now unequivocal.

Mechanisms that have driven past global climate shifts are diverse. They arguably include meteorite impact, changes in solar influx, and orbital cycles. Throughout geologic time, greenhouse gas has also undeniably served as instigator or accomplice in abrupt climate shifts.

Compelling evidence for the role of greenhouse gas in past warming and cooling is provided by stable oxygen isotopes, atmospheric carbon measured with the dual parameters of stable carbon isotopes, and leaf stomata. We are also aware of the timing, amount and types of gas emitted by past major volcanic eruptions and other sources.

Four well-documented past climatic shifts serve as guideposts for today. Each was accompanied by major extinctions, or major shifts in planetary life. The causes and effects of each of the following events will be discussed:
1) The Devonian extinction, 370 million years ago;
2) The Permian extinction, 250 million years ago;
3) The Triassic extinction, 210 million years ago;
4) The Paleocene - Eocene extinction, 55 million years ago.

The geologic record offers compelling lessons for today’s climate crisis. First, greenhouse gases DO affect climate—and life on Earth--dramatically and lethally.

Second: Greenhouse gas is being added to the atmosphere at geologically unprecedented rates.

Third, whereas volcanoes were common villains in the past; today, human energy use and generation are the major sources of greenhouse gas. While the geologic record may seem remote, it offers compelling lessons for today’s climate crisis. Unless we suppress human greenhouse emissions, and develop renewable, low carbon energy sources, the consequences for ecosystems in today’s change will echo past experiences.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas