First published 20120718 / last updated on 20120924
Is climate change the worst nightmare scenario for our future? We know it is there to stay, and experts tell us daily about what we are to expect (note 2). Nevertheless, the science of impacts is a very uncertain business, because it relies – through models and analogies – on two independent guesses (usually called scenarios, projections or hypotheses) about the (1) impacted system (our societies at large, or agriculture, or human health) and (2) the extreme factor that causes the impact. It may happen, though, that the magnitude of some geophysical factors is so extreme that it can lead only to a profound and lasting disruption of the impacted system. This note makes the point that our society as a whole is far more vulnerable to the climatic consequences of large volcanic eruptions than to green-house gas induced climate change. It woudn’t be the first time, in fact, that volcanic eruptions threaten to wipe out mankind (Ambrose, 1998). We do not even mention meteorite impacts, that could obliterate higher forms of life – and give another chance to cockroaches to dominate the world! In the wake of other authors, I argue that the “familiar” volcanic eruptions can lead to the end of civilization. Maybe we would be well inspired to spend some effort to try and understand if there is life beyond volcanic winter.
I first came across the concept of volcanic winter in 1979, in a paper published in Scientific American by Stommel and Stommel. The authors describe how aerosol (note 3 and wikipedia) injected into the atmosphere by the eruption of Tambora (Java) in 1815 was eventually distributed worldwide by 1816, resulting in the reduction of solar radiation at ground level. This profoundly affected climate, decreasing temperature and reducing sunshine, which in turn lead to catastrophic crops in 1816 over much of the northern hemisphere. The resulting suffering is amply documented in the scientific and anecdotal literature (for examples of anecdotal reports,note 5.)
Depending on their size, type and location, eruptions lead to a variable mix of local and global consequences on various socio-economic sectors. We not interested here in the local consequences (refer to note 6 for different types of eruptions and some impacts on agriculture). The effect may last for several years, as illustrated: the figure shows stratospheric aerosol concentrations between 1979 and 1995. In the case of Mt Pinatubo (June 1991 eruption), a well studied event because of its magnitude (McCormick, et al., 1995, Hansen et al., 1996), the global temperature decrease was about 0.5°C. Additional details can be found in Schönwiese 1988, Briffa, et al. 1998 and de Silva et al. 1998. See Bradley and Jones (1992) for a list of historically recent eruptions. Also note that some eruptions are known by their climatic and demographic effects (for instance the “mysterious” 1258 eruption, “mysterious” because there seems to be little understanding about which volcano actually caused the effects (Stothers, 2000).
Next to not-so-well-known eruptions, there are some which have received a lot of attention, such as the 1815 eruption of Tambora. It is widely used as a small scale analogue of a nuclear winter (Sagan and Turco, 1990), the drop of temperature that would result from a large scale “nuclear exchange”.
In fact, there is a large volume of literature on nuclear winter (both science and fiction, e.g. The Road, by Cormac McCarthy), with nuclear winter being usually seen as more “dangerous” than volcanic winter (compare: note 4.) An easily accessible and comprehensive overview of the effects of large volcanic eruptions is given by Self, 2006. According to Robock (2011), the drop in temperature resulting from the detonation of 100 nuclear bombs (releasing 5 million tonnes of black carbon, note 7) would be around 1.3 standard deviations (referred to the 1951-80 period). The drop in solar radiation would reach 16 watts/m² and take about 10 years to return to normal. Also see Robock et al., 2007; Robock et al., 2007a and Toon et al., 2007 for a more detailed analysis of the climatic and other effects of nuclear winter. The worst scenario in Robock et al (2007a) entails a global temperature drop of close to 8 degrees and a rainfall drop close to 45%. But more than anything else, nuclear war and winter would entail hunger over several years, with crop growing season shortening by as much as 60 days in worst hit areas (Toon et al., 2007a.). In 1816, the global impact lasted about one and a half years, but larger eruptions would have larger and longer-lasting impacts.
The book has one simple message: a couple of major volcanic eruptions has the potential to completely disrupt our way of life, our societies and existing equilibria. The author convincingly argues that the human history after the 6th century got profoundly affected by the volcanic eruptions in the 530s: they changed the course of history worldwide.
According to Keys, there are currently nine restless craters that represent a significant threat to the world’s future economic and political well-being:
- Yellowstone, host to the world’s largest dormant volcano—a huge caldera covering around fifteen hundred square miles;
- a currently dormant supervolcano in Long Valley, California;
- the caldera known as the Campanian/Campi Flegrei complex, which is becoming increasingly restless. Interestingly, a paper by Costa et al. (2012) just got a lot of attention in the general and popular-scientific press. The paper deals with the eruption of the Phlegrean complex about 39000 years ago. Results reveal that the CI eruption dispersed 250 to 300 km³ of ash over 3.7 million km². The eruption marks distinct bio-cultural changes inWestern Eurasia, termed the Middle to Upper Palaeolithictransition. Archaeological sites covered by the CI ash often have clear post-eruption sterile layers indi-cating that occupation in the region changed, even at sites characterized by millennial-long continuous occupation[…]. In addition, the youngest Neanderthal fossils in the Caucasus region are older than –40-39 ka […] allowing the possibility that combination of the eruption and Heinrich Event 4 (HE4) led to a demographic crash in the region.
- Rabaul, in Indonesia, also currently displaying ominous signs of increasing restlessness
- five other large and potentially active caldera volcanoes in the Alaskan Aleutian Islands and Mexico
If any one of them was to explode, world climate would be plunged into chaos, precisely as it was in the sixth century. But with world population at forty times its sixth-century level, the death toll would almost certainly run into the hundreds of millions. And just as history was resynchronized fourteen and a half centuries ago, a future caldera eruption, through its climatic impact, would almost certainly destabilize the economic and geopolitical status quo, leading to a second resynchronization of history […] Given the experience of the sixth-century eruption and its consequences, yet taking into account the more integrated nature of the modern world, I believe that a similar catastrophe today would ultimately shift the balance of geopolitical power away from the West and in favor of the Third World
Also consider that recent (2012) articles have shown that Potentially Civilization-Ending Super-Eruptions may Have Surprisingly Short Fuses (Blundy and Rust, 2012; Druitt et al., 2012). The subtitle of the article by Druitt et al. is A petrology study of the Bronze Age ‘Minoan’ eruption on the Greek island of Santorini finds that the sub-volcanic magma reservoir was recharged in spurts during the decades to months that preceded the eruption. In other words: there will be little little warning!
Volcanic winter is a climatic consequence of large volcanic eruptions; it has the potential to profoundly disrupt the world as we know it. Compared with greenhouse gas triggered climate change, volcanic winter sets on rapidly, and with little warning. It also lasts only a couple of years. Due to the magnitude of the disruption, there is quite some certainty about impacts, i.e. chaos, hunger, and a shift of political power to the southern hemisphere. On the other hand, climate change is already there, even if the effects are mild, long lasting and more uncertain; but we can prepare for it.
Article 2 of the Framework Convention on climate change states that The ultimate objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Many papers have been written about the interpretation of “dangerous interference”. There is little doubt, however, that the dangerousness of volcanic winter by far exceeds the one of climate change. As such, it certainly deserves more attention than it currently gets.
Note 1: this is partly based on Gommes,2003
Note 2: We are told (Solomon et al., (2009) that the increase of atmospheric CO2 – and it’s effects – will probably be irreversible for 1000 years. Climate change is there to stay, and we must learn to live with it. I have written elsewhere about my doubts regarding climate catastrophism… Unfortunately, the fashion of the day is (1) to resort to climate change to explain about everything (e.g. Brown and Crowford, 2009.); (2) everyone is now a climate “expert”, and the “experts” are rediscovering what experts have known for decades: it is symptomatic that some of the old texts are being reprinted, for instance Jackson 1977, Chang 1968 & Lamb 1982. It is a paradox that climate science has progressed immensely over the last 20 years and yet there is more naive approaches to impacts than ever before!
Note 3: Volcanic aerosol is a mixture of fine solid particles and droplets of liquid. Major volcanic eruptions blow large amounts of dust and gases into the lower stratosphere (15–25 km) where winds may distribute them over the globe in a matter of weeks or months. It is particularly sulphuric acid (derived from a combination of sulphur dioxide and water) that plays a significant role in increasing the Earth’s albedo, usually resulting in lower surface temperatures.
Note 4: Brighter than a thousand suns could end up in darker than a thousand nights!
Note 5: starting around 1810, German municipalities were requested to prepare an annual „municipality chronicle“ (Gemeindechronik) which included quantitative data on population by gender (including immigration/emigration), agriculture (crops and livestock), health etc. The chronicles provide very valuable information on conditions prevailing in rural areas. The summer of 1816 and the potato blight of 1845 are well described. For instance, Conrads (1938) writes about Kalterherberg, a village now on the German-Belgian border, that the years 1816 and 1817 were emergency years. The crop failure in the cold and wet year 1816 (rain and fog) resulted in a terrible price increase. Most crops did not mature and were still in the fields around mid-October, when they were killed by early frost. 1817 was a year of famine. About the neighbouring village of Lammersdorf, Conrads reports that in the spring of 1817 grass, nettles, clover and other feedcrops were not fed to catlle. Instead, they were „cooked to a pulp“ and consumed by hungry families. Many people had to emigrate, driven by hunger. In another nearby village (Höfen), April 1816 was cold and frosty, and on 15 May there was still snow remaining from winter. On the 6th of June, it snowed again! From then until late fall, it rained almost constantly. At Michaelmas (end of September, http://en.wikipedia.org/wiki/Michaelmas), oats had not matured yet. After harvesting in November, sleges were used to take the harvest to the villages; many places did not harvest and just left the crops in the fields. The quality of wheat and oats was very bad, and so was the bread: it could be baked only with the utmost difficulty, because it wouldn’t „hold together“. Very many potatoes were lost to frost and remained in the ground.
Note 6: Types of volcanic eruptions. Volcanic eruption classifications range from Hawaiian (quiet eruptions with fluid lava) to Pelean (very violent eruptions accompanied by nuées ardentes and avalanches of explosive lava); Stiegeler, 1976. The nuées ardentes (literally “burning clouds”) are high pressure and high temperature gas and ashflows moving at speeds of up to 100 km/h. They transport large amounts of debris and pose very serious threats. The most violent type of eruption – Pelean – leaves very little chance to escape, burns all living creatures and results in widespread destruction. The Mount Vesuvius eruption that buried Pompei in 79 was of that type. Of course, there is more to worry about today than in the first century, because Mount Vesuvius is very close to Naples (Barnes, 2011). Even a very “orderly” and less populated place (Naples has 3 million inhabitants!) place would be almost impossible to evacuate.
Eruptions are usually accompanied by both lava flows (with local effects, i.e. effects usually within a range of 10 to 100 km) and wider ranging atmospheric phenomena. We all remember the April 2010 eruption of Eyjafjallajökull, which paralized air traffic over part of Europe. Another famous Icelandic eruption occurred during 1783, over 12 km3 of lava and 500 million tonnes of noxious gases were emitted during the Laki Fissure eruption (McGuire, 1997.)
The local effects of volcanic eruptions can also be devastating, for example, no terrestrial species survived the eruption of Krakatoa on 26 and 27 August 1883. The eruption caused more than 35 000 human victims as a result of the tsunami rather than the volcanic eruption directly (McGuire, 1997).
Effects tend to be relatively local only if the ash is not injected into the upper atmosphere. By way of an example, the 1989 (18 May) Mount St. Helens eruption in Washington State reached Idaho and Montana where large quantities of volcanic ash littered the soil to a depth of 1 m in places.
As shown by the eruption of Etna (Chester, et al., 1985) lava flows have the potential to cause structural damage and will destroy any buildings in their path.
But most important is the fact that prime agricultural land is rapidly “inundated” and can become unsuitable for agriculture and other related activities for hundreds of years. The above mentioned Pinatubo eruption on Luzon in the Philippines (1991), the largest volcanic eruption of the 20th century, covered villages and agricultural land with sterile ashes, to the extent that around 150 000 people were made homeless and 600 000 lost their livelihoods. The ash blanket reached a depth of several metres in the valleys close to the mountain, reducing to an average depth of 5 cm at a radial distance of 40 km. An estimated 5 000 km2 was affected. Some of the most fertile land in the Philippines had to be abandoned, leading to immediate damage and loss of future income. Mudflows created havoc in flat areas up to 50 km from the crater, by, for instance, clogging fishponds. An estimated 326 000 ha of forest, 43 000 ha of cropland and 16 000 ha of ponds were damaged. Even in 1992, mudflows still occurred and buried crops (Rantucci, 1994).
On the positive side, it should be mentioned that where ash does not exceed 10 cm, it can be ploughed in and will increase productivity due to its pH, P, K, Ca and Mg, even if Fe and S are excessive (according to Rantucci). Similarly, Besoain, et al., (1992), found the deposits from the Lonquimay volcano in Chile between 1988 and 1990 had improved local soil quality.
Rantucci provides a detailed breakdown of the total loss incurred to the economy due to the Mount Pinatubo eruption (Table 8.1). Agriculture accounts for 59.7 per cent of the total economic loss, most of it in the forestry sector and in the form of lost revenue.
Finally, a special mention should be made of the 1986 (21–24 August) “eruption” of Lake Nyos (north-west Cameroon) which was characterized by major CO2 and H2S emissions (Youxue Zhang, 1996). The toxic mixture caused about 3 000 deaths and in Nyos village only 2 of a population of 700 survived. Poultry and cattle experienced heavy losses.
Note 7: black carbon is the sooth emitted into the atmosphere by fires (especially cities) resulting from a nuclear exchange.
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