Warme Winter nach großen Vulkanausbrüchen in den Tropen

Thema heute: Vulkane. Starke Vulkanausbrüche schleudern ihre schwefelhaltige Asche bis in die Stratosphäre, wo die Teilchen für wenige Jahre die Sonne verdunkeln und die globalen Temperaturen erniedrigen. Man erinnert sich an: Das Jahr ohne Sommer 1816. Für Einsteiger in das Thema sei dieser Beitrag von Javier auf WUWT von 2018 empfohlen.

Wir schauen heute nach, was es Neues zum Thema Vulkane und Klima in der Wissenschaft gibt. Im Jahr 2017 stellte die NASA ein neues Kartenwerk vor, in dem die Schwefeldioxid-Emissionen der Vulkane der Welt per Satellit kartiert wurden. Hier bei der NASA nachlesen. Das Paper ist von Carn et al. 2017. Schön wäre natürlich auch so eine Karte mit vulkanischen CO2-Emissionen. Ob die noch irgendwann kommt?

Als zwischen 2000-2014 die globalen Temperaturen stagnierten, war guter Rat teuer. Einige Wissenschaftler versuchten den Hiatus mit kleinen Vulkanausbrüchen zu rechtfertigen. Das war natürlich ziemlich Quatsch, denn es war der PDO-Ozeanzyklus der damals negativ war. Nun brachten Stocker et al. 2019 ein weiteres Paper zum Thema heraus. Sie fanden, dass kleine Vulkane lediglich „bis zu 20% des Temperaturtrends ausmachen, je nach Höhenstufe und geographischer Breite. Abstract:

Quantifying Stratospheric Temperature Signals and Climate Imprints From Post‐2000 Volcanic Eruptions

Small volcanic eruptions and their effects have recently come into research focus. While large eruptions are known to strongly affect stratospheric temperature, the impacts of smaller eruptions are hard to quantify because their signals are masked by natural variability. Here, we quantify the temperature signals from small volcanic eruptions between 2002 and 2016 using new vertically resolved aerosol data and precise temperature observations from radio occultation. We find characteristic space‐time signals that can be associated with specific eruptions. In the lower stratosphere, robust warming signals are observed, while in the midstratosphere also cooling signals of some eruptions appear. We find that the volcanic contribution to the temperature trend is up to 20%, depending on latitude and altitude. We conclude that detailed knowledge of the vertical structure of volcanic temperature impacts is crucial for comprehensive trend analysis in order to separate natural from anthropogenic temperature changes.

Zambri et al. 2017 beschreiben in einer Arbeit, dass der auf starke tropische Vulkanausbrüche folgende Winter meist ungewöhnlich warm ist. Der darauffolgende Sommermonsunregen ist typischerweise verringert. Abstract:

Northern Hemisphere winter warming and summer monsoon reduction after volcanic eruptions over the last millennium

Observations show that all recent large tropical volcanic eruptions (1850 to Present) were followed by surface winter warming in the first Northern Hemisphere (NH) winter after the eruption. Recent studies show that climate models produce a surface winter warming response in the first winter after the largest eruptions but require a large ensemble of simulations to see significant changes. It is also generally required that the eruption be very large, and only two such eruptions occurred in the historical period: Krakatau in 1883 and Pinatubo in 1991. Here we examine surface winter warming patterns after the 10 largest volcanic eruptions between 850 and 1850 in the Paleoclimate Modeling Intercomparison Project 3 last millennium simulations and in the Community Earth System Model Last Millennium Ensemble. These eruptions were all larger than those since 1850. Though the results depend on both the individual models and the forcing data set used, we have found that models produce a surface winter warming signal in the first winter after large volcanic eruptions, with higher temperatures over NH continents and a stronger polar vortex in the lower stratosphere. We also examined NH summer precipitation responses in the first year after the eruptions and find clear reductions of summer Asian and African monsoon rainfall.

Vulkangeschichte: Wir schreiben das Jahr 1257 n. Chr. als der Samalas-Vulkan in Indonesien ausbrach. Die Mittelalterliche Wärmeperiode kam gerade zu einem Ende, da setzte dieser Mega-Ausbruch einen starken Kälteimpuls. Lesen Sie die Geschichte in Guillet et al. 2017:

Climate response to the Samalas volcanic eruption in 1257 revealed by proxy records

The eruption of Samalas in Indonesia in 1257 ranks among the largest sulfur-rich eruptions of the Common Era with sulfur deposition in ice cores reaching twice the volume of the Tambora eruption in 1815. Sedimentological analyses of deposits confirm the exceptional size of the event, which had both an eruption magnitude and a volcanic explosivity index of 7. During the Samalas eruption, more than 40 km3 of dense magma was expelled and the eruption column is estimated to have reached altitudes of 43 km. However, the climatic response to the Samalas event is debated since climate model simulations generally predict a stronger and more prolonged surface air cooling of Northern Hemisphere summers than inferred from tree-ring-based temperature reconstructions. Here, we draw on historical archives, ice-core data and tree-ring records to reconstruct the spatial and temporal climate response to the Samalas eruption. We find that 1258 and 1259 experienced some of the coldest Northern Hemisphere summers of the past millennium. However, cooling across the Northern Hemisphere was spatially heterogeneous. Western Europe, Siberia and Japan experienced strong cooling, coinciding with warmer-than-average conditions over Alaska and northern Canada. We suggest that in North America, volcanic radiative forcing was modulated by a positive phase of the El Niño–Southern Oscillation. Contemporary records attest to severe famines in England and Japan, but these began prior to the eruption. We conclude that the Samalas eruption aggravated existing crises, but did not trigger the famines.

Die Uni Bristol hat 2017 herausgefunden, dass es mehr Superausbrüche gegeben hat als gedacht. Pressemitteilung hier. Paper dazu ist Rougier et al. 2018.

University of Maryland im Februar 2019 zur Vulkangeschichte der letzten 2600 Jahre:

Revising the history of big, climate-altering volcanic eruptions

New method, co-developed at UMD, refines the 2,600-year history of large eruptions that inject planet-cooling particles into the stratosphere

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.

IOP Publishing am 17.9.2019 (via ScienceDaily):

Role of Tambora eruption in the 1816 ‚year without a summer‘

A new study has estimated for the first time how the eruption of Mount Tambora changed the probability of the cold and wet European ‚year without a summer‘ of 1816. It found that the observed cold conditions were almost impossible without the eruption, and the wet conditions would have been less likely.

1816 recorded exceptionally low global temperatures, with central and Western Europe seeing a particularly cold and wet summer that led to widespread agricultural failures and famines. The 1815 eruption of Mount Tambora in Indonesia has long been assumed to have been the cause, with a link made as early as 1913. Now, using historical data and modern modelling techniques, researchers led by the University of Edinburgh, UK, have estimated just how important the eruption was. They publish their findings today in Environmental Research Letters.

The study’s lead author, Dr Andrew Schurer, from the University of Edinburgh, said: „The eruption of Mount Tambora in April 1815 was among the most explosive of the last millennium. It had an enormous impact locally, devastating the island of Sumbawa. The eruption injected a huge amount of sulphur dioxide (SO2) into the stratosphere, which would have quickly spread across the world, oxidising to form sulphate aerosols. „These volcanic aerosols reduce net shortwave radiation causing widespread, long lasting surface cooling. They also lead to a reduction in global rainfall, while wettening some dry regions, and causing dynamic changes in the large-scale circulation of both ocean and atmosphere.“

The research team used early instrumental data, combined with new climate simulations from two different models, to conduct an event attribution analysis. Their aim was to determine if, and by how much, the volcanic forcing affected the probability of cold and wet conditions in this ‚year without a summer‘. Their results, from summers with similar sea-level-pressure patterns to 1816, using both observations and unperturbed climate model simulations, show that the circulation state can reproduce the precipitation anomaly without external forcing, but only explains about a quarter of the anomalously cold conditions.

Dr Schurer said: „Including volcanic forcing in climate models can account for the cooling, and we estimate it increases the likelihood of the extremely cold temperatures by up to 100 times. „Although the observed sea-level pressure pattern can account for much of the observed anomalously wet conditions, even without volcanic forcing, there is strong evidence in the model simulations that the volcanic eruption increases the chance of such a wet summer over Central Europe, by about 1.5 to three times.

„Mount Tambora played a dominant role in causing the observed cold conditions, and probably also contributed to the anomalously wet conditions. Without volcanic forcing, it is less likely to have been as wet and highly unlikely to have been as cold.“

Paper: Andrew P Schurer, Gabriele C Hegerl, Jürg Luterbacher, Stefan Brönnimann, Tim Cowan, Simon F B Tett, Davide Zanchettin, Claudia Timmreck. Disentangling the causes of the 1816 European year without a summer. Environmental Research Letters, 2019; 14 (9): 094019 DOI: 10.1088/1748-9326/ab3a10

Aubry et al. 2016 schüren Angst, dass zukünftige Vulkanausbrüche ihre Asche nicht mehr so oft in die Stratosphäre schleudern werden – wegen des Klimawandels. Lächeln bitte. Story auf WUWT.

Vulkane brechen aus, wann sie Lust haben, nicht wann der Mensch es gerne hätte. Die kühlende Wirkung der Vulkane für das Erdklima lässt sich daher schlecht planen. Bethke et al. 2017 kritisieren, dass man eine viel breitere Bandbreite von Ausbruchsszenarien in die Temperaturzukunftsprognosen einbauen müsste. Abstract:

Potential volcanic impacts on future climate variability

Volcanic activity plays a strong role in modulating climate variability1. Most model projections of the twenty-first century, however, under-sample future volcanic effects by not representing the range of plausible eruption scenarios2,3,4. Here, we explore how sixty possible volcanic futures, consistent with ice-core records5, impact climate variability projections of the Norwegian Earth System Model (NorESM)6 under RCP4.5 (ref. 7). The inclusion of volcanic forcing enhances climate variability on annual-to-decadal timescales. Although decades with negative global temperature trends become ∼50% more commonplace with volcanic activity, these are unlikely to be able to mitigate long-term anthropogenic warming. Volcanic activity also impacts probabilistic projections of global radiation, sea level, ocean circulation, and sea-ice variability, the local-scale effects of which are detectable when quantifying the time of emergence8. These results highlight the importance and feasibility of representing volcanic uncertainty in future climate assessments.

Abschließender Videotipp:

Dr. Sebastian Lüning: Vulkane, die schwarzen Schwäne der Evolution? (10. IKEK)