Guest post by Steven Goddard
Scientific American recently reported on the dodgy concept that climate change causes volcanoes, when in fact it is quite the opposite.
In 1883, Krakatoa produced massive amounts of ash during an eruption estimated to the equivalent of 200 megatons – or 13 times larger than the Hydrogen Bomb detonated at Bikini Island. Average global temperatures dropped by about 1.2°C during the following year as a result of ash blocking the sun.
It has been hypothesized by a volcanologist at Los Alamos, that the Dark Ages were triggered by agricultural collapse following the 535AD eruption of Krakatoa.
Modern history has its origins in the tumultuous 6th and 7th centuries. During this period agricultural failures and the emergence of the plague contributed to: (1) the demise of ancient super cities, old Persia, Indonesian civilizations, the Nasca culture of South America, and southern Arabian civilizations; (2) the schism of the Roman Empire with the conception of many nation states and the re-birth of a united China; and (3) the origin and spread of Islam while Arian Christianity disappeared. In his book, Catastrophe An Investigation into the Origins of the Modern World, author David Keys explores history and archaeology to link all of these human upheavals to climate destabilization brought on by a natural catastrophe, with strong evidence from tree-ring and ice-core data that it occurred in 535 AD.
With no supporting evidence for an impact-related event, I worked with Keys to narrow down the possibilities for a volcanic eruption that could affect both hemispheres and bring about several decades of disrupted climate patterns, most notably colder and drier weather in Europe and Asia, where descriptions of months with diminished sun light, persistent cold, and anomalous summer snow falls are recorded in 6th-century written accounts. Writings from China and Indonesia describe rare atmospheric phenomena that possibly point to a volcano in the Indonesian arc. Although radiocarbon dating of eruptions in that part of the world are spotty, there is strong bathymetric and volcanic evidence that Krakatau might have experienced a huge caldera eruption. Accordingly, I encouraged a scientific expedition to be led by Haraldur Sigurdsson to the area.
The expedition found a thick pyroclastic deposit, bracketed by appropriate radiometric dates, that suggests such a caldera collapse of a Proto-Krakatau did occur perhaps in the 6th century. Bathymetry indicates a caldera some 40 to 60 km in diameter that, with collapse below sea level, could have formed the Sunda Straits, separating Java from Sumatra, as suggested by ancient Javanese historical writings. Such a caldera collapse likely involved eruption of several hundred cubic kilometers of pyroclastic debris, several times larger than the 1815 eruption of Tambora. This hypothetical eruption likely involved magma-seawater interaction, as past eruptions of Krakatau document, but on a tremendous scale. Computer simulations of the eruption indicate that the interaction could have produced a plume from 25 to >50 km high, carrying from 50 to 100 km3 of vaporized seawater into the atmosphere. Although most of the vapor condenses and falls out from low altitudes, still large quantities are lofted into the stratosphere, forming ice clouds with super fine (<10 micrometer) hydrovolcanic ash.
Discussions with global climate modelers at Los Alamos National Laboratory led me to preliminary calculations that such a plume of ash and ice crystals could form a significant cloud layer over much of the northern and southern hemispheres. Orders of magnitude larger than previously studied volcanic plumes, its dissipation and impact upon global albedo, the tropopause height, and stratospheric ozone are unknown but certainly within possibilities for climate destabilization lasting years or perhaps several decades. If this volcanic hypothesis is correct, the global, domino-like effects upon epidemics, agriculture, politics, economics, and religion are far-reaching, elevating the potential role of volcanism as a major climate control, and demonstrating the intimate link between human affairs and nature.
More recent volcanic events which lowered global temperatures, were the 1991 eruption of Mount Pinatubo and the 1983 eruption of El Chichón.
A 2002 study reported in Science demonstrated that feedback from water vapor in the atmosphere was largely responsible for the 1984 cooling.
Global Cooling After the Eruption of Mount Pinatubo: A Test of Climate Feedback by Water Vapor
The explosion is estimated to have been at scale 7 on the Volcanic Explosivity Index. It had roughly four times the energy of the 1883 Krakatoa eruption. An estimated 160 cubic kilometers (38 cubic miles) of pyroclastic trachyandesite was ejected, weighing approximately 1.4×1014 kg (see above).This has left a caldera measuring 6–7 km (3.7–4.3 mi) across and 600–700 m (2,000–2,300 ft) deep. The density of fallen ash in Makassar was 636 kg/m². Before the explosion, Mount Tambora was approximately 4,300 metres (14,100 ft) high, one of the tallest peaks in the Indonesian archipelago. After the explosion, it now measures only 2,851 metres (9,354 ft).
The 1815 Tambora eruption is the largest observed eruption in recorded history (see Table I, for comparison). The explosion was heard 2,600 kilometres (1,600 mi) away, and ash fell at least 1,300 kilometres (810 mi) away. Pitch darkness was observed as far away as 600 kilometres (370 mi) from the mountain summit for up to two days. Pyroclastic flows spread at least 20 kilometres (12 mi) from the summit.
Mt. St Helens erupted 30 years ago next month. Like the Icelandic volcanoes, it was covered with thick ice and snow.
Meltwater from the ice and snow contacted the rising magma, leading to a huge amount of steam pressure and a massive explosion on May 18 following the collapse of the north flank.
I was involved in some experimental research around that time, which demonstrated that the amount of ash and the explosivity of volcanoes is primarily dependent on the amount of water which comes in contact with the magma underground. It can be concluded that the glaciers in Iceland are contributing to the ash, not the other way around – and that volcanoes cause climate change, not the other way around.
Brian J. Soden,1* Richard T. Wetherald,1 Georgiy L. Stenchikov,2 Alan Robock2The sensitivity of Earth’s climate to an external radiative forcing depends critically on the response of water vapor. We use the global cooling and drying of the atmosphere that was observed after the eruption of Mount Pinatubo to test model predictions of the climate feedback from water vapor. Here, we first highlight the success of the model in reproducing the observed drying after the volcanic eruption. Then, by comparing model simulations with and without water vapor feedback, we demonstrate the importance of the atmospheric drying in amplifying the temperature change and show that, without the strong positive feedback from water vapor, the model is unable to reproduce the observed cooling. These results provide quantitative evidence of the reliability of water vapor feedback in current climate models, which is crucial to their use for global warming projections.