A Climatic Discovery
Contact: John Roth, 541-592-2100 x 2230
"Some people are weatherwise, but most are otherwise." Benjamin Franklin must have known that weather isn't rocket science. It is way more complicated than that. The state of the atmosphere from minutes to months is weather. Climate is the weather of a place averaged for at least several years, plus extreme events. Some climate patterns may last longer than a human lifetime. So even the most climate-wise scientists don't know how much they vary or if the changes are cyclic.
A November article in the journal Nature Communications by five researchers from Oregon State University, Oxford, and the University of Minnesota, brings new insight to long term climate change. A National Science Foundation grant allowed OSU graduate student Vasile Ersek (now at Oxford University) to sample a broken stalagmite at Oregon Caves in the southwestern part of the state. The result, according to Dr. Alan Mix, a co-author of the study, is a past climate record that, for its length, detail, and precision, may be among the world's best. Samples were taken at such closely spaced time intervals as to approach the resolution of the world's longest ice cores. And of course Oregon's climate differs from that of Greenland or Antarctica. This treasure trove of sharply imaged data will yield new ways to understand climate for many years to come.
It is now known that weather in the Eastern Pacific is affected every few years by an El Niño or a La Niña, warm and cool events respectively for Oregon but which start in the tropics. This multi-year fluctuation is also known as the El Nino/ Southern Oscillation or ENSO for short. ENSO spins off atmospheric waves that travel over most of the planet. So it probably impacts more people than any other climate pattern. Yet nobody knew this until just a few decades ago.
It's also only been known since the 1980s that the North Pacific has a longer climate cycle, the Pacific Decadal Oscillation (PDO). Since a single cycle of the PDO takes from twenty to thirty years, not enough events have been studied in detail to understand what causes the PDO or ifthe two cycles affect each other. Different ratios of El Niños to La Niñas seem so far to be associated with different PDO phases, a cool (negative) phase with more La Niñas and a warm (positive) phase with more El Niños. In Oregon, the weather is cool and wet during La Niñas and negative PDOs and drier and warmer during El Niños and positive PDOs.
Some experts liken the El Niño /La Niña cycle to a tuning fork that ramps up and/or vibrates faster or slower when ENSO is in or out of phase with the PDO or other cycles. But not knowing what may cause PDOs has prevented accurate predicting of when it will switch to a new phase.
The notion that even tiny changes in sunlight may affect both the frequency and strength of climate oscillations has been around for a while. A typical PDO period is in a range that holds the main 22 year solar cycle. However, many researchers argue that there have been too few cycles to make sure that the link between the sun's output and Earth's climate in the last few centuries isn't just by chance.
The ratios of different isotopes of carbon and oxygen trapped in limestone like stalagmites depend on the amount of water seeping into a cave, the temperature, and the type of vegetation above the cave. Such changes over time in these rock mounds help climatologists figure out how hot it was and how much rain fell. At Oregon Caves, measured stalagmite samples from the last 13,000 years make one of the strongest cases yet that slight changes in sunlight can affect climate.
How might Oregon's weather be affected by changes in sunlight and ocean currents? When areas near the Pacific equator are unusually warm, as in an El Nino event, cool, dense air blows in from the north to equalize pressures. But this wind is deflected by the Earth's rotation as westward moving trade winds. Changes in solar activity may shift this state out of neutral by evaporating more seawater in the subtropics and moving it into the trade winds. The wet winds heat up and rise as they approach Asia. The increased vertical motion pulls in the more horizontal east to west trade winds.
In response to these air motions, the Aleutian low pressure zone of the North Pacific moves to the south and east. This cold system picks up moisture from warmer seawater and rains descend on Oregon Caves. The opposite occurs during times of tropical cooling; then Oregon has warmer, drier winters, as the Aleutian Low moves back to the north.The response isn't rapid; it takes some time for the ocean to adjust, and the lag time creates a self-sustaining phase change. This cycle may be changed by external changes, such as how much of the sun's energy reaches Earth.
The new data from Oregon Caves suggests that heating from high solar activity might shift a PDO into a negative phase, the part of the oscillation that has cooler waters off of Oregon.
An earlier, presumably negative PDO interval saw heavy snows at Oregon Caves and the Dust Bowl (1932-1939) further south, both events that started some eighty years ago.
Once again, drought prevails over America's heartland, raising food prices across the nation. It also is so much warmer at the Caves in most winters now that years of increased precipitation yield more rain than snow and thus rapid runoff. Long term residents of the Illinois Valley say that some streams that ran year round back in the 1930s now dry up in summer before they reach the Illinois River. Land use or misuse likely exasperated summer drought in both areas but La Niñas played a role as well.
In recent decades, storms, cloud cover, glacial melting, and acidic seawater are changing faster than most current models predict. That may mean the models need to be refined. The Oregon Caves data will help refine such models to better fit the real world so as to prepare for the future.
The scientific jury is still out as to whether the one third rise in greenhouse gases has affected either the PDO or ENSO cycle in the last century. Unfortunately, the Oregon stalagmites' calcite stopped growing during this time interval. Nevertheless, the earlier cycles suggest that the solar cycle change of just a few tenths of one percent of sunlight energy reaching Earth may be amplified into much greater climate and ocean changes. The human-caused greenhouse effect likely has already added at least that amount of energy, suggesting that further changes in Oregon's climate are likely. The ongoing results of mankind's greatest experiment should give us all pause. Our changing climate is already impacting rivers, salmon, forests, rugged coasts, and other icons of the "Pacific Northwest."
Did You Know?
Carbon dioxide mixes with water that condenses on the wall of the cave to create a very weak acid. Over long periods of time this "acid dew" eats away at the marble walls of Oregon Caves making the cave larger.