By Bryce Gray, Katherine Dempsey and Sarah Kramer
Dec 03, 2014
You might want to think of climate researchers as arson investigators.
That’s the comparison made by Penn State climate scientist Richard Alley at the Comer Abrupt Climate Change Conference this fall in southwestern Wisconsin.
“You would very much want your arson investigator to know what a natural fire looks like, because if you’re going to accuse someone of starting a fire, you better know that nature didn’t do it,” said Alley. “We as climate historians learn what nature has done so that we can tell if what’s going on now is natural.”
Scientists who are piecing together the potential impact of Earth’s current climate crisis keep looking back – thousands and even millions of years into the past.
That’s because understanding where human-driven climate change is headed first requires developing that intimate knowledge of the factors that have influenced climate throughout Earth’s history.
Alley and other top climate researchers from across the country presented their latest findings at the Comer Abrupt Climate Change Conference in southwestern Wisconsin this fall.
Beyond determining the extent to which “our fingerprint” is affecting major processes that regulate global climate, Alley said that looking at historical precedents also provides a glimpse of what might be in store as fossil fuel use pushes concentrations of carbon dioxide to levels not seen in the past 10 to 15 million years.
“By helping to understand the patterns of climate change in the past, we learn the mechanisms, we learn the patterns, and so we help project what will happen in the future and how our actions could affect that.”
Scientists at the conference brought clues from research findings in Greenland, the Arctic, Mongolia, Bhutan and other places around the globe where they measured glacial earthquakes, cored ice for ancient air bubbles, mapped the contraction of lakes and collected rocks hit by cosmic rays as a time machine to document past warming and cooling.
Geochemist Wallace Broecker, of Columbia University, peered back 50 million years at a time when the land mass of India was on the move and collided into Asia. “That changed the course of the Earth’s environment,” he said. “The collision put the Earth on a new course and the main importance of that course is that it cooled the earth.”
One lesson from the paleoclimate research is clear: As climate changes, a corresponding shift of the thermal equator has major consequences for human populations.
The thermal equator in turn impacts precipitation. “The rain belts could shift south,” said climate researcher Jeffrey Severinghaus of the University of California, San Diego. “And then you have a billion people in Asia who depend, for their livelihood, on the monsoon, not being able to grow their crops.”
The thermal equator is a band of high temperatures encircling the Earth near the geographic Equator. The geographic boundary never changes but the thermal equator can shift in tandem with global changes. Climatic shifts in the North Atlantic, for instance, typically precede those in the Southern Hemisphere, Severinghaus said.
Under natural circumstances, these events can occur more than a thousand years before worldwide warming sets in, but their effects are drastic. Now, human-triggered climate change threatens to make these patterns more severe.
Previously, the cooling and warming of the hemispheres represented shifts within stable modes of global climate patterns, according to Severinghaus. However, the excess carbon dioxide associated with human-driven climate change could shift the Earth into an entirely new mode – spelling trouble for human population centers, he said.
Severinghaus also revealed troubling evidence that carbon dioxide levels can rise rapidly, rather than the gradual increase previously thought to occur, due to a positive feedback loop from the soil of the Earth that causes rapid jumps in atmospheric CO2.
Carbon dioxide levels associated with fossil fuel emissions already have risen more than 33 percent during the Industrial Age compared to the previous 800,000 years. And the levels are acting like a thermostat increasing global temperatures. The research of glacial expert Brenda Hall showed similar shifts in thinking regarding paleoclimate patterns that offer a clearer understanding of where climate could be headed now.
Hall’s work in the Tierra del Fuego determined that glaciers retreated quickly at the end of the last major ice age that reached its maximum 20,000 years ago. Entire ice sheets collapsed in less than 1,000 years, according to Hall – a mere blink of an eye in geologic time. Over the last two centuries, Hall said, we’ve seen a similar retreat, but with different causes. “One was a big, end-of-the-ice-age warming,” she said, “the other is warming over the last century – some of which almost certainly is natural warming and some of which is human-induced.”
Scientists are also using clues from old shorelines to observe past wet and dry periods over thousands of years so they can tie these periods to climate changes.
Nevada State Climatologist Douglas P. Boyle studies past shorelines at closed boundary lakes such as Nevada’s Walker Lake, which are particularly sensitive to fluxes in climate. His team produces lake-level simulations using hydrologic and atmospheric models and historic data. At the Comer Conference, he showed scientists how rising levels signify cooling and falling lake levels signify warming. His preliminary field findings resulted from research conducted with others at the University of Nevada, Reno, where he is an associate professor of geography.
“We can try to figure out how those climates existed and why they existed and how the earth responded to those climates to give us just a better understanding of climate change, why it happens and what are the impacts,” Boyle said.
One period of focus is the Medieval Climatic Anomaly, a heat wave that struck the Great Basin of the U.S. with two “megadroughts.” One of these megadroughts spanned 240 years, 850 to 1,090 A.D., and the other one spanned at least 180 years – 1140 to 1320 A.D. Furthering knowledge of megadroughts will be pivotal in regions expected to contend with drier, warmer conditions wrought by global warming, Boyle said.
Meanwhile, seismologist Meredith Nettles of Columbia University discussed glacial calving – the process of ice breaking off a glacier – and how low tides might be linked to the collapse of ice sheets that send icebergs the size of Central Park crashing into the ocean.
She presented data from observations at Greenland’s Helheim Glacier, linking tides and the occurrence of earthquakes, presumably triggered by the ice breaking. A low tide corresponded to more earthquakes. The glacier stretches out more with low tide and stretching any material makes it break, Nettles explained. Calving models indicate that breaking through the ice is needed for an iceberg to separate.
Taken as a whole, these and other findings from across the globe paint a grim picture of the climate-related challenges facing our warming planet. U.N. climate delegates meeting in Lima, Peru, this month agreed on the draft of a deal to reduce fossil fuel emissions and stop global warming at or near 2 degrees Celsius (3.6 degrees Fahrenheit), the tipping point for widespread melting ice and sea level rise. Temperatures have already risen nearly 1 degree C.
But where some see daunting obstacles, Alley sees a future brimming with opportunities for society to reinvent itself and build a more robust economy, driven by eco-friendly alternative energies.
“Across a huge amount of scholarship, there’s strong agreement that starting now to deal with fossil fuels, to reduce them and switch to other things, makes us better off,” Alley said, emphasizing that such a shift would simultaneously rid the atmosphere of harmful pollutants while also stimulating job creation.
“This is not about losing money – this is about gaining money,” Alley said.
Moreover, Alley believes that human beings find themselves at an exciting crossroads – one where we are able to “get off the treadmill” of dependency on convenient but finite energy sources.
“We’ve always been hunter-gatherers of energy, looking for the next thing and then over-hunting it, over-gathering it, and then looking for the next thing,” Alley said. “For the first time in human history we actually can see a way to build something that will power everyone essentially forever.”
Alley, Broecker and University of Maine glaciologist George Denton help organize the conference hosted by the Comer Family Foundation and philanthropist Gary Comer’s children Stephanie and Guy Comer.
They help coordinate the foundation’s continuing climate change research program that backs innovative young researchers with Comer funding, a continuing legacy to Gary Comer who died of prostate cancer in 2006.