In June 1991, when Mt. Pinatubo in the Philippines spewed tons of volcanic ash and gases into the atmosphere, it just so happened that halfway around the world scientists were beginning to obtain good data from carbon dioxide monitors high above the tree canopy in Harvard Forest, outside Boston, Mass. Now, more than a decade later, the measurements taken during the years following the eruption are providing new insight into how atmospheric aerosols affect photosynthesis. The findings, published today in the journal Science, are forcing scientists to rethink the factors that influence the cycling of carbon through the environment, particularly carbon dioxide, a major player in global warming.
Within three weeks of the Mt. Pinatubo eruption, the largest volcanic blast of the century, a band of sulfur aerosol had encircled the globe. By early 1992, the volcanic gases and aerosols had diffused through the stratosphere, veiling the earth. During that time, global carbon dioxide levels fell more sharply than any other decline on record. Some scientists suggested that global cooling caused ecosystem respiration to drop, lowering the amount of carbon dioxide emitted into the atmosphere. But Lianhong Gu of Oak Ridge National Laboratory, lead author of the Science report, didn’t think that could be the only explanation.
Gu knew that crop scientists had discovered that plants grow best in diffuse light. When sunlight is too intense, some leaves fall into shadow, unable to photosynthesize, while others bask in the direct beams but will reach a photosynthetic saturation point. Moderate cloud cover and aerosols block direct beams, but allow light to bounce back and forth off water vapor and other molecules, creating a “softer” light that reaches leaves that would otherwise be shaded. As a result, the plants photosynthesize more, using up carbon dioxide in the process. Gu and his collaborators determined that the same principles apply to forest canopies. The Harvard Forest data show that carbon dioxide levels dropped for two years following the eruption at Mt. Pinatubo findings that the scientists suggest represent a worldwide phenomenon given that the eruption had a global atmospheric effect. “Up until now we hadn’t linked aerosols and clouds with carbon studies,” Gu says. “In order to understand atmospheric carbon dioxide concentrations, which affect climate, we have to look at how aerosols and clouds affect the global carbon cycle.”
SUMMARY:A simple model of the CO2 concentration of the atmosphere is presented which fairly accurately reproduces the Mauna Loa observations 1959 through 2018. The model assumes the surface removes CO2 at a rate proportional to the excess of atmospheric CO2 above some equilibrium value. It is forced with estimates of yearly CO2 emissions since 1750, as well as El Nino and La Nina effects. The residual effects of major volcanic eruptions (not included in the model) are clearly seen. Two interesting finding are that (1) the natural equilibrium level of CO2 in the atmosphere inplied by the model is about 295 ppm, rather than 265 or 270 ppm as is often assumed, and (2) if CO2 emissions were stabilized and kept constant at 2018 levels, the atmospheric CO2 concentration would eventually stabilize at close to 500 ppm, even with continued emissions.
A recent e-mail discussion regarding sources of CO2 other than anthropogenic led me to revisit a simple model to explain the history of CO2 observations at Mauna Loa since 1959. My intent here isn’t to try to prove there is some natural source of CO2 causing the recent rise, as I think it is mostly anthropogenic. Instead, I’m trying to see how well a simple model can explain the rise in CO2, and what useful insight can be deduced from such a model.
The model uses the Boden et al. (2017) estimates of yearly anthropogenic CO2 production rates since 1750, updated through 2018. The model assumes that the rate at which CO2 is removed from the atmosphere is proportional to the atmospheric excess above some natural “equilibrium level” of CO2 concentration. A spreadsheet with the model is here.
Here’s the assumed yearly CO2 inputs into the model:
Fig. 1. Assumed yearly anthropogenic CO2 input into the model atmosphere.
I also added in the effects of El Nino and La Nina, which I calculate cause a 0.47 ppm yearly change in CO2 per unit Multivariate ENSO Index (MEI) value (May to April average). This helps to capture some of the wiggles in the Mauna Loa CO2 observations.
The resulting fit to the Mauna Loa data required an assumed “natural equilibrium” CO2 concentration of 295 ppm, which is higher than the usually assumed 265 or 270 ppm pre-industrial value:
Fig. 2. Simple model of atmospheric CO2 concentration using Boden et al. (2017) estimates of yearly anthropogenic emissions, an El Nino/La Nina natural source/sink, after fitting of three model free parameters.
Click on the above plot and notice just how well even the little El Nino- and La Nina-induced changes are captured. I’ll address the role of volcanoes later.
The next figure shows the full model period since 1750, extended out to the year 2200:
Fig. 3. As in Fig. 2, but for the full model period, 1750-2200.
Interestingly, note that despite continued CO2 emissions, the atmospheric concentration stabilizes just short of 500 ppm. This is the direct result of the fact that the Mauna Loa observations support the assumption that the rate at which CO2 is removed from the atmosphere is directly proportional to the amount of “excess” CO2 in the atmosphere above a “natural equilibrium” level. As the CO2 content increases, the rate or removal increases until it matches the rate of anthropogenic input.
We can also examine the removal rate of CO2 as a fraction of the anthropogenic source. We have long known that only about half of what is emitted “shows up” in the atmosphere (which isn’t what’s really going on), and decades ago the IPCC assumed that the biosphere and ocean couldn’t keep removing excess CO2 at such a high rate. But, in fact, the fractional rate of removal has actually been increasing, not decreasing.And the simple model captures this:
Fig. 4. Rate of removal of atmospheric CO2 as a fraction of the anthropogenic source, in the model and observations.
The up-and-down variations in Fig. 4 are due to El Nino and La Nina events (and volcanoes, discussed next).
Finally, a plot of the difference between the model and Mauna Loa observations reveals the effects of volcanoes. After a major eruption, the amount of CO2 in the atmosphere is depressed, either because of a decrease in natural surface emissions or an increase in surface uptake of atmospheric CO2:
Fig. 5. Simple model of yearly CO2 concentrations minus Mauna Loa observations (ppm), revealing the effects of volcanoes which are not included in the model.
What is amazing to me is that a model with such simple but physically reasonable assumptions can so accurately reproduce the Mauna Loa record of CO2 concentrations. I’ll admit I am no expert in the global carbon cycle, but the Mauna Loa data seem to support the assumption that for global, yearly averages, the surface removes a net amount of CO2 from the atmosphere that is directly proportional to how high the CO2 concentration goes above 295 ppm. The biological and physical oceanographic reasons for this might be complex, but the net result seems to follow a simple relationship.
Weather forecasters know that some models work better than others in specific situations, and they tend to rely on the versions that work best, depending upon the forecast problem. When the issue is a potential big snow along the eastern seaboard, forecasters usually lean upon the model from the European Center for Medium-Range Weather Forecasting (the “Euro” model). When diagnosing shifts in jet stream patterns a week or 10 days ahead, they may place more weight on the American Global Forecast System model.
But the United Nations’ Intergovernmental Panel on Climate Change simply averages up the 29 major climate models to come up with the forecast for warming in the 21st century, a practice rarely done in operational weather forecasting. As dryly noted by Eyring and others “there is now evidence that giving equal weight to each available model projection is suboptimal.”
While tooling around the internet, I ran into a report about an upcoming article in Geophysical Research Letters.
“To assess whether the airborne fraction is indeed increasing, Wolfgang Knorr of the Department of Earth Sciences at the University of Bristol reanalyzed available atmospheric carbon dioxide and emissions data since 1850 and considers the uncertainties in the data.
In contradiction to some recent studies, he finds that the airborne fraction of carbon dioxide has not increased either during the past 150 years or during the most recent five decades.
I was surprised to learn that someone thought that CO2 hadn’t gone up. After all we have the famous Keeling Curve.
It has wonderful geometric beauty, and that implies a certitude about the CO2 levels.
Now, while I won’t necessarily support Knorr’s conclusions or methods, he did spur me to look again at the measurements of CO2 in the atmosphere. It spurred me to ask a question: Why is the Keeling Curve so geometrical?
Let’s start by looking at the CO2 measurements at the South Pole. There is nothing geometrical about it.
How about Baring Head, NZ?
Clearly the Keeling curve looks artificial compared to the other stations on earth. One could say that maybe the other researchers are simply incompetent, but that seems harsh. Why is the Keeling curve so regular, especially since it is sitting on a volcano that occasionally spews out additional CO2? In 40 years has not one single measurment been taken when the volcano was blowing additional CO2 towards the station? That seems highly unlikely.
Below are all the Pacific stations plotted together. Note the scatter. After subtracting the trend of all these temporally aligned measurments, the standard deviation is 6 ppm. Yet the Keeling curve claims, implicitly, accuracy less than 1 ppm.
But these stations all start in the 1950s. What gives? Were there no measurements of atmospheric CO2 prior to that time? Sadly, the IPCC and Keeling, simply ignore the vast literature on previous CO2 measurements.
Ernst-Georg Beck published a paper analysing the 90,000 measurments of atmospheric CO2 from 1812 to the present. It is at Beck, Ernst-Georg, “180 years of atmospheric CO2 gas analysis by chemical methods” Energy and Environment 18,(2007):2, pp. 259-282
The story his analysis tells is a big blow to the climate hysteriacs, who seem never to access or mention CO2 measurments made by chemical analysis over this span. The IPCC uses the ice cores, which, in light of 90,000 atmospheric measurments of CO2 over the past 200 years gives the appearance of cherry-picking. A short version of a peer reviewed paper is found here
Let’s first look at Beck’s chart showing the historical measurments. One immediately sees that CO2 was higher than the ‘consensus’ IPCC scientists would allow. They use the ice core data and ignore actual atmospheric measurements.
Now lest someone say that this kind of high CO2 levels were unusual, look at the bi-weekly data from Giessen, Germany for the years 1939-1941.
The IPCC graphs don’t mention or show the variations in CO2 turned up by Beck here and see the picture below. The IPCC is clearly cherry-picking the data. Look at the insert below.
At the very least, the IPCC should explain specifically why it is rejecting all these historical measurments of CO2. As it is, they act as if these measurements don’t exist.
There have been voluminous headlines, photos, and video describing eruptions on Hawaii’s Kilaueua in 2018, and while they were visually impressive, when it comes to potentially climate altering sulfur dioxide, those eruptions pale in comparison to another Pacific volcano.
NASA Earth observatory writes:
While Kilauea dominated headlines last year, the largest explosive eruption of 2018 occurred 5,600 kilometers (3,500 miles) to the southwest on Ambae, a volcanic island in Vanuatu. The Manaro Voui volcano spewed at least 400,000 tons of sulfur dioxide into the upper troposphere and stratosphere during its most active phase in July, and a total of 600,000 tons in 2018. That was three times the amount released from all combined eruptions in 2017.
Stratospheric sulfur dioxide concentrations on July 28, 2018 Credit: OMPS Suomi-NPP
The map above shows stratospheric sulfur dioxide concentrations on July 28, 2018, as detected by the Ozone Mapping Profiler Suite (OMPS) on the Suomi-NPP satellite. The volcano on Ambae (also known as Aoba) was near the peak of its sulfur emissions at the time. For perspective, emissions from Hawaii’s Kilauea and the Sierra Negra volcano in the Galapagos are shown on the same day. The plot below shows the July-August spike in emissions from Ambae.
SO2 data from July 10 – August 31, 2018
“With the Kilauea and Galapagos volcanoes, you had continuous emissions of sulfur dioxide over time, but Ambae was more explosive,” said Simon Carn, professor of volcanology at Michigan Tech. “There was a giant pulse in late July, and then it dispersed.”
During a series of eruptions at Ambae in 2018, volcanic ash blackened the sky, buried crops, and destroyed homes. Acid rain turned the rainwater—the island’s main source of drinking water—cloudy and “metallic, like sour lemon juice,” said New Zealand volcanologist Brad Scott. Over the course of the year, the island’s population of 11,000 was forced to evacuate several times.
The OMPS instruments on the Suomi-NPP and NOAA-20 satellites contain downward-looking sensors, which can map volcanic clouds and measure sulfur dioxide (SO2) emissions by observing reflected ultraviolet light. SO2 and other gases (such as ozone) each have a spectral absorption signature, or unique fingerprint, that OMPS can measure and quantify.
“Once we know the SO2 amount, we put it on a map and monitor where that cloud moves,” said Nickolay Krotkov, a atmospheric scientist at NASA’s Goddard Space Flight Center. The maps, which are produced within three hours of a satellite overpass, are used by volcanic ash advisory centers to predict the movement of volcanic clouds and to reroute aircraft, if necessary.
At the peak of the Ambae eruption, a powerful burst of energy pushed gas and ash into the upper troposphere and stratosphere. The natural-color image above was acquired on July 27, 2018, by the the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP.
SO2 is short lived in the atmosphere, but once it penetrates the stratosphere, it can combine with water vapor to make sulfuric acid aerosols. Such particles can last much longer—weeks, months or even years—depending on the altitude and latitude of injection, Carn said.
In extreme cases, like the 1991 eruption of Mount Pinatubo, the tiny aerosol particles can scatter so much sunlight that they cool Earth’s surface below. “We think to have a measurable climate impact, the eruption needs to produce 5 to 10 million tons of SO2,” Carn said. The Ambae eruption was too small to cause such cooling.
“This wasn’t huge, it wasn’t Pinatubo,” Carn said. “But it was the biggest one of the year.”
New method, co-developed at UMD, refines the 2,600-year history of large eruptions that inject planet-cooling particles into the stratosphere
From the UNIVERSITY OF MARYLAND
For all their destructive power, most volcanic eruptions are local events. Lava flows tend to reach only a few miles at most, while airborne ash and soot travel a little farther. But occasionally, larger eruptions can launch particles into the stratosphere, more than 6 miles above Earth’s surface. The 1991 eruption of Mount Pinatubo in the Philippines–the world’s largest eruption in the past 100 years–is a prime example of a stratospheric eruption.
When volcanic particles reach the stratosphere they stay aloft for a long time, reflecting sunlight and temporarily cooling the planet. By understanding the history of these big eruptions, researchers can begin to place short cooling episodes and other discrete climate events into the context of large-scale climate patterns.
Researchers working at the University of Maryland, the Université Grenoble Alpes in France, the Ecole Normale Supérieure in France and the Tokyo Institute of Technology have devised a new, more accurate system for identifying large stratospheric eruptions recorded in the layers of Antarctic ice cores.
Using their method, the researchers made some important revisions to the known history of big eruptions–correcting the record on several misidentified events while discovering a few as yet unknown stratospheric eruptions. The researchers described their approach, which identifies airborne volcanic particles with a specific chemical signature, in a paper published January 28, 2019, in the journal Nature Communications.
“I find it very exciting that we are able to use chemical signals to build a highly accurate record of large, climate-relevant stratospheric eruptions,” said James Farquhar, a professor of geology at UMD and a co-author of the research paper. “This historical record will be highly useful for climate scientists seeking to understand the role of large eruptions in climate oscillations. But there is also the basic marvel of reading a chemical fingerprint that is left behind in ice.”
Eventually, volcanic particles fall from the stratosphere, settling on the ground below. When they land on snow, the particles get covered up by more snow that gets compacted into ice. This preserves a record of the eruption that survives until the ice melts. Researchers can drill and retrieve ice cores in places like Antarctica and Greenland, revealing eruption records that stretch back several thousand years.
Because particles from large stratospheric eruptions can spread across the globe before falling to the ground, previous methods identified stratospheric eruptions by looking for sulfate particle layers in ice from both hemispheres–usually from Antarctica and Greenland. If the same layers of sulfate showed up in both cores, deposited at the same time in Earth’s history, researchers would conclude that the particles came from the same large, stratospheric eruption.
“For eruptions that are intense enough to inject material into the stratosphere, there is a telltale signature in the sulfur isotope ratios of sulfate preserved in ancient ice layers,” explained Farquhar, who also has an appointment in UMD’s Earth System Science Interdisciplinary Center. “By instead focusing on this distinct sulfur isotope signature, our new method yielded some surprising and useful results. We found that prior reconstructions missed some stratospheric events and falsely identified others.”
The study’s lead author, Elsa Gautier from the Université Grenoble Alpes, did a significant portion of the analyses at UMD while on a Fulbright scholarship to work with Farquhar in 2013. Following Gautier’s lead, the researchers developed their method using ice cores collected at a remote site in Antarctica called Dome C. One of the highest points on the Antarctic ice sheet, Dome C is home to ice layers that stretch back nearly 50,000 years.
Gautier and her colleague Joel Savarino, also at the Université Grenoble Alpes, collected ice cores at Dome C that contain records stretching back roughly 2,600 years, covering a large portion of recorded human history.
The researchers used their method to confirm that many events had indeed been properly identified by the older method of matching up corresponding sulfate layers in ice cores from both hemispheres. But some events, formerly thought to be big stratospheric eruptions, did not have the telltale sulfur isotope signature in their sulfate layers. Instead, the researchers concluded, these layers must have been deposited by two or more smaller volcanoes that erupted at about the same time at high latitudes in both hemispheres.
The researchers also found some big stratospheric events that contain the isotope signature, but were somehow constrained to the Southern Hemisphere.
“This is a strength of our approach, because these events would have a climate impact but are missed by other methods,” Farquhar said. “We have made a significant improvement to the reconstruction of large stratospheric eruptions that occurred over the past 2,600 years. This is critically important for understanding the role of volcanic eruptions on climate and possibly for understanding certain events in human history, such as widespread famines. It can also help to inform future climate models that will take large volcanic events into account.”
The research paper, “2600 years of stratospheric volcanism through sulfate isotopes,” Elsa Gautier, Joel Savarino, Joost Hoek, Joseph Erbland, Nicolas Caillon, Shohei Hattori, Naohiro Yoshida, Emanuelle Albalat, Francis Albarede and James Farquhar, was published in the journal Nature Communications on January 28, 2019.
The Katla volcano, hidden beneath the ice cap of Mýrdalsjökull glacier in Iceland, has historically erupted violently once every 40-80 years. In-as-much as it’s last such eruption took place one hundred years ago, in 1918, Katla’s next eruption is long overdue.
An eruption in Katla would dwarf the 2010 Eyjafjallajökull eruption, scientists have warned.
A new study by Icelandic and British geologists showed that Katla is emitting enormous quantities of CO2 – at least 20 kilotons of CO2 every day. Only two volcanoes worldwide are known to emit more CO2, Evgenia Ilyinskaya a volcanologist with the University of Leeds told the Icelandic National Broadcasting Service RÚV.
These enormous CO2 emissions confirm significant activity in the volcano, Evgenia told RÚV: “There must also be a magma build up to release this quantity of gas.”
“It is well known from other volcanoes,” said Evgenia, “that CO2 emissions increase weeks or years ahead of eruptions. This is a clear sign we need to keep a close eye on Katla…. there is something going on.”
The largest glacial flood in Iceland’s history occurred in the beginning of the Katla eruption in 1918. Tales of this flood are terrifying. Although it was a thick mixture of meltwater, volcanic ash, and ice, it advanced so fast that one could only escape its path on horseback. It covered hundreds of square kilometers; today such a flood would destroy the Iceland ring road and many important facilities in the south of the country.
Excellent discussion of [CO2], RH, and feedbacks. Lively discussion in the comments. Nick Stokes, George Smith, and Pamela Grey join the article’s author in debate on climate models and assumptions regarding RH: Is it constant or not? Good reading.
Water vapor feedback has remained a topic of debate since 1990. The laymen do not know that water has an essential role in calculating the warming effects of GH gases. In all Anthropogenic Global Warming (AGW) models the Relative Humidity (RH) stays constant. It sounds like a very neutral and harmless assumption. When GH gases increase the atmospheric temperature, the constant RH means that the absolute amount of atmospheric water also increases. Because water is about a 15 times stronger GH gas than carbon dioxide, this small increase of water content increases the temperature as much as GH gases. According to IPCC, the radiative forcing of GH gases is doubled by water (AR3 and AR4). IPCC calls this feature a positive feedback of water.
According to my spectral analysis calculations, the positive water feedback effect would be this magnitude. But in AR5 (20139 IPCC…
Fig. 2. Simple model of atmospheric CO2 concentration using Boden et al. (2017) estimates of yearly anthropogenic emissions, an El Nino/La Nina natural source/sink, after fitting of three model free parameters.
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