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Volcano Watch — Mauna Loa Observatory: The Keeling Curve recognized as landmark science

April 23, 2015

On April 30, 2015, the National Oceanic and Atmospheric Administration (NOAA) and the American Chemical Society will commemorate Earth's pre-eminent modern atmospheric carbon dioxide (CO2) record started at the Mauna Loa Observatory, a NOAA atmospheric research facility located at 3,350 m (11,000 ft) above sea level on Mauna Loa's north flank.

As part of this recognition, the CO2 data set itself will become officially recognized as a National Historic Chemical Landmark.

Continuous CO2 monitoring began on Mauna Loa in 1958, when Charles David Keeling installed state-of-the-art instrumentation high on the remote north flank of the volcano and began carefully measuring the amount of CO2 in the air. This new data became crucial to an ongoing discussion about whether the CO2 released by industrial processes, such as power generation, was building up in Earth’s atmosphere.

Once established, the record showed convincingly that CO2 buildup was indeed taking place. In fact, the technique worked so well that during summer months it easily detected the seasonal uptake of CO2 by increased vegetation. During winter months, when foliage in the northern hemisphere is scarcer, CO2 levels measured at the Mauna Loa location climbed. This seasonal trend superimposed on the long term increasing background atmospheric CO2 record has since been demonstrated at a parallel measurement location in Barrow, Alaska.

But Mauna Loa is also an active volcano, and USGS Hawaiian Volcano Observatory (HVO) scientists are sometimes asked if gas released from the mountain affects the ambient CO2 values reported by MLO. The short answer is no. Although instrumentation at MLO can easily detect CO2 emissions from the rift and summit caldera emission sources when winds blow from that direction, MLO scientists are careful to exclude these data from the background CO2 record.

Remarkably, MLO staff have shown how to use these volcanically "contaminated" CO2 records to actually estimate the amount of CO2 discharged by the volcano. Their published findings show that Mauna Loa, when it's not erupting, releases a fraction of the CO2 emitted by its younger and more exuberant neighbor, Kīlauea. USGS measurements during Mauna Loa's most recent eruption in 1984 found emissions comparable with Kīlauea's current daily rate—about 15,000 tons per day.

Fifteen thousand tons—an amount equivalent to the annual emissions from 2,400 sport utility vehicles—is a lot of CO2. However, careful examination of global volcanic CO2 emissions by USGS scientist Terry Gerlach showed that only during rare and very large explosive eruptions do total volcanic emission rates come close to the rate of CO2 produced in the modern industrialized world. For example, the same amount of CO2 emitted during the 9-hour catastrophic eruption of Mount St. Helens in 1980 is released every 2.5 hours by human activity. On average, though, the proportion released by volcanoes is much less. All of Earth's volcanoes taken together emit less than one percent of the CO2 produced each year by humans.

The data set that Charles David Keeling established nearly 50 years ago at MLO, which eventually became known as the "Keeling Curve," is truly worthy of the recognition it will receive next week. Besides documenting the steady upward trend of CO2 concentration in Earth's atmosphere, this precise and modern CO2 record has been used to reconstruct temperature and CO2 concentration records as far back as 500,000 years ago. To accomplish this, scientists combined the current record, global temperature data, and studies of CO2 and deuterium isotope concentrations found in the air trapped in ice cores.

Keeling's modern record, along with the ice core studies, show conclusively that CO2 concentrations in the atmosphere are higher than they've been in at least half a million years. They also show that the sharpest and most significant CO2 increase coincided with Earth's industrialization, and that this increase is mimicked by average global temperatures.

The news isn't all bad, though. As climate scientists work to understand implications of the MLO CO2 record, other data sets at the observatory, inspired partly by Keeling's work, are documenting progress towards lowering human-generated greenhouse gases, such as chlorofluorocarbons. As HVO continues to study what goes on beneath the surface of Hawaiian volcanoes, we applaud the Mauna Loa Observatory's efforts to better understand the workings of Earth's atmosphere.


Volcano Activity Update

Kīlauea Volcano's East Rift Zone lava flow continues to feed widespread breakouts northeast of Pu‘u ‘Ō‘ō. The front of the breakout farthest downslope was 8 km (5 mi) from Pu‘u ‘Ō‘ō on Thursday, April 23.

Kīlauea's summit began to inflate on Tuesday, April 21, and was still inflating as of Thursday. The lava level in the summit lava lake rose in concert, and was 21 m (70 ft) below the rim of the Overlook crater at midday on Thursday, April 23. This is the highest level reached by the lava lake since the summit eruption started in 2008. Seismicity also increased at the summit and along the upper East Rift Zone.

Three earthquakes were reported felt in Hawaii this past week. On Sunday, April 19, 2015, at 7:47 a.m., HST, a magnitude-2.3 earthquake occurred 12.3 km (7.6 mi) southwest Laupāhoehoe, Hawai‘i, at a depth of 16.8 km (10.5 mi). On Monday, April 20, at 9:18 p.m., HST, a magnitude-3.2 earthquake occurred 11.1 km (6.9 mi) NE of Ke‘anae, Maui, at a depth of 14.9 km (9.2 mi). On Tuesday, April 21, at 11:02 p.m., HST, a magnitude-2.4 earthquake occurred 8.0 km (5.0 mi) E of Waiki‘i, Hawai‘i, at a depth of 25.3 km (15.7 mi).

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