A Short History of Climate Change: Important Lessons from the Past.
By Ellen Morris Bishop, Oregon Paleo Lands Institute
Earth’s climate has never been stable. Throughout planetary history, we have varied from a frigid snowball earth to a tropical, ice-free orb. These ancient climate changes provide resounding lessons for today’s shifts. Past climate changes have lead to the Earth’s greatest extinctions, including eradication of more than 90 percent of global life and most are correlated with the rise and fall of greenhouse gases.
How, you might wonder, can we determine atmospheric composition and temperatures from so long ago? Geologists and paleontologists rely on both chemical and fossil evidence to understand past climates.
We can calculate past temperatures by measuring oxygen isotopes (the ratio of “normal” O16 to O18, it’s heavier equivalent) in sea-floor sediments and in the clays of ancient soils. This reliable ratio has been evaluated and tested many times in the laboratory.
Ancient carbon dioxide levels are recorded in fossil leaves—specifically, in the number and size of leaf stomata (or breathing holes) per square centimeter of leaf area. Other climate indicators include carbon isotopes (C12 and C13), leaf shape and clay minerals in ancient soils. Periods of extensive glaciation leave behind ice-worn grooves, and a distinctive type of sedimentary deposit. Periods of global warmth support widespread corals, tropical vegetation, and limestones.
The geologic record shows clearly that today’s climate change is happening at a much faster pace than even the most rapid rate of geologic change. The most rapid known rate of greenhouse gas and temperature increases occurred 55 million years ago. It was a time that was already globally warm. There were no polar ice caps, and Oregon was, literally a banana belt. Fossil leaves found in the John Day Fossil Beds include bananas, palms, and ancestral citrus. Pendleton looked like a Mississippi bayou. At 56 to 60 million years ago, atmospheric CO2 likely ranged around 800 to 1000 ppm, and global average temperatures of about 70 degrees in contrast to today’s nearly 400 ppm levels, and average global temperature of 60 degrees, demonstrating the power of greenhouse warming.
But a rapid rise in temperatures above even these at precisely 55 million years ago (the end of the Paleocene period) threw ecosystems out of kilter, and exterminated nearly 35% of marine life, as well as 25% of known animal life on land. The cause? Eruptions of voluminous lava flows on the sea floor. These volcanic eruptions belched vast amounts of CO2 into the atmosphere. They heated the sea floor unleashing frozen seafloor methane. Altogether, about 600 billion tons of carbon was placed into the atmosphere in about 10,000 years. Temperatures soared to a global average of about 78 degrees. It took the globe at least 100,000 years to return to its former temperatures and CO2 levels.
Today, humans inject 6 billion tons of carbon into the atmosphere EACH YEAR. At present rates, we will out-do the total ancient sea floor effusions and eruptions before the end of this century.
Just as in the Paleocene, ecosystems today cannot adjust to rapidly rising temperatures and shifting precipitation. Human-driven extinctions are already considered the planet’s 6th major extinction. With any luck, we might make it to the level of the third greatest extinction, at the end of the Triassic, when temperatures also spiked, and global greenhouse gas increased.
What we want to avoid, at all costs, is rivaling the climate-driven Permian extinction, some 250 million years ago. While this seems like a long time, it has happened within the most recent 5% of earth’s history. Again, vast eruptions filled the atmosphere with CO2 and other gases. Again, temperatures soared. Oxygen fell to perhaps 12 percent of the atmosphere. CO2 exceeded 4000 ppm. Global average temperatures may have been as high as 140 degrees. And more than 90 percent of life perished.
So we toy with the atmosphere at our peril. For at least the past 38 million years, the globe has been slowly cooling. This record is eloquently displayed in the John Day Fossil Beds, where dark red tropical laterite soils of 45 million years ago grade upward into light-colored tan soils of a temperate climate. Fossil wood demonstrates that our temperate, seasonal climate has been with us since only 35 million years ago. But now, almost any climate change graph, whether temperature or CO2, demonstrates that we are on a steep and slippery slope, poised, perhaps, to follow dimetreodons, pantodonts, and even Oregon’s state fossil, the Metasequoia, into the abyss of time.
Today, we cannot blame this increase in greenhouse gas on a giant volcano. There is no super-eruption of methane from the sea floor. To find the source of rising atmospheric greenhouse gases, we need only look in the mirror, and paraphrase Pogo—“We have met the volcano, and it is us.”
But there is hope, if we act. The movement toward Energy Independence is crucial. We must try new technologies, and practice conservation. Please take action. Life is depending on you.
