We have learned an enormous amount about our planet’s climate system by studying Earth’s modern and recent history -- roughly the last two million years, and particularly the last 10,000 to 100,000 years. Climate models of that recent period benefit from our knowledge of continental distribution and elevation, oceanic circulation, and atmospheric composition. We can collect data from ancient ice that contains samples of past atmospheres. And we can get information at a resolution of millennia, centuries, or sometimes even shorter periods -- well within human comprehension.
Yet that recent record represents a minuscule slice of Earth’s history -- only four 10-thousandths of the planet’s 4.5-billion-year existence. It is, in effect, the 0.04 percent solution. But does the first 99.96 percent of Earth’s history really matter? We’re here now. It’s more important for us to understand the present and the imminent future than to probe a past obscured in Earth’s deep time.
Or is it?
Earth’s deep-time record includes climate states that seem very alien. Research over the last decade has revealed states and rates of climate change that astound even the geoscientists making the discoveries, including the presence of icebergs in equatorial oceans and palm trees in Wyoming. Those conditions are so far beyond the realm of human experience as to seem irrelevant. Yet they are relevant because they are not beyond the realm of possibilities on Earth.
They remind us that Earth is capable of more than we’ve imagined. They involve and yield insight into multiple components of Earth’s climate system -- biosphere, atmosphere, hydrosphere, lithosphere -- giving us access to the full spectrum of natural variability in the system. For those reasons they provide key data for climate-model experiments and calibration: What better way to test the models than by mining the wealth of experiments recorded in Earth’s own lab book, and using the data to push models to their limits? Our understanding of major components of the climate system, like the effects of clouds and atmospheric dusts, is marred by huge uncertainties that affect models’ predictions; data from deep time could clarify them for us.
That Earth’s climate has included extremes far beyond what humans have experienced consoles some people. But we are demonstrably moving out of the comfort zone of human experience, and our future could well hold conditions like those of deep time.
Consider our “modern” climate. We live in an “icehouse” -- a climate phase characterized generally by the presence of large continental ice sheets. Ice began to grow in Antarctica 34 million years ago, and in the Northern Hemisphere about 2.5 million years ago. Human civilization developed during the relatively stable, recent interglacial phase of that bipolar icehouse. Of the last 500 million years, only 80,000 -- or less than 0.02 percent -- have experienced that particular climate state. Humans evolved during, and are thus adapted to, an atypical climate state.
We have significantly altered Earth’s land surfaces, oceans, and atmosphere, particularly since the onset of widespread use of fossil fuels. From the bubbles of ancient atmospheres trapped in ice cores, we have reconstructed levels of CO2, a well-known greenhouse gas, from the past 400,000 years -- which seems like forever to most of us, and in fact is forever in the context of our species. Those data demonstrate that atmospheric C02 values have remained within a narrow range, between about 190 and 280 parts per million. In terms of C02, the composition of the air that humans have breathed has not varied much, until now.
In the brief period since the Industrial Revolution, we’ve burst that envelope, with atmospheric C02 currently at nearly 380 ppm and rising. That rate of change far exceeds any variations found in the ice-core record, and it cannot be attributed to natural causes. The air that my grandchildren will breathe will contain more C02 than any air on Earth in the past 20 million years or more. No human -- not even any member of another hominid species -- so far has experienced such elevated levels of C02.
The magnitude of the change we’re witnessing -- a projected doubling or tripling of C02 within the next century -- will warm Earth by an average 3°C, according to most models. That planetary average is misleading, however, because the change will be unevenly distributed; some regions will experience significantly greater increases. Although such temperatures are not new on Earth, they have no precedent in human history, and no precedent in Earth’s recent geologic history.
In a real sense, then, we are returning to deep time, and thus it is both relevant and urgent for us to study deep-time climate. Our hopes to predict Earth’s future rest on our abilities to grasp the principles that have dictated its distant past. The 0.04 percent solution is obsolete.
We need a concerted national effort to analyze data from, and refine models of, deep time. The foundation is in place. Scientists can now measure atmospheric C02, land and ocean temperatures, precipitation, winds, and other climatic parameters from deep time at relatively fine resolutions. For instance, we can trace grains of dust blown in the wind to detect seasonal variations in atmospheric circulation that occurred 300 million years ago.
Several large projects sponsored by the National Science Foundation are revolutionizing our ability to understand Earth’s deep-time record, as well as data archiving and retrieval. A new effort being discussed by earth scientists would use systematic, broad-scale continental drilling to produce high-resolution data; once researchers had those data, they could pursue interdisciplinary studies through standard grants from the NSF and other agencies.
Research on Earth’s deep-time climate has traditionally been the purview of a small group of geologists; as it becomes increasingly important, experts in atmospheric sciences, oceanography, biology, and related disciplines must become involved, too, so we can seamlessly integrate the deep-time and near-time records. And because all of us will be affected by future global change, the new knowledge must become part of the standard science curricula -- it will be necessary background for students when they need to understand major policy decisions in the future.
Born and raised in an icehouse, our species is moving into a greenhouse. If we are to survive the change, we will need to understand more than just 0.04 percent of our planet’s history.
G.S. (Lynn) Soreghan is an associate professor of geology at the University of Oklahoma at Norman and chair of the steering committee for GeoSystems, a community-development project supported by the National Science Foundation to encourage research on Earth’s deep-time climate record.
http://chronicle.com Section: The Chronicle Review Volume 51, Issue 45, Page B10