Thursday, July 2

A natural contributor to climate change


TODAY the very words ‘climate change’ seem to be on everyone’s tongue for, inevitably, much attention has been focussed on manmade or artificial atmospheric pollutants. I should like to bring the reader’s attention to natural atmospheric pollutants which have and can lead to short-term changes in our weather patterns and subsequently affecting man and animals.

This article focusses on 1815, the very year that Napoleon Bonaparte was defeated by the Duke of Wellington on Sunday, June 18, at the Battle of Waterloo. A major factor leading to Napoleon’s defeat was the incessant rainfall that summer, which literally bogged down his troops on lower ground. But, what contributed to this was a massive input of volcanic ash into the atmosphere two months before.

Mount Tambora blows its top

Located on the island of Sumbawa, Indonesia, Mount Tambora erupted on April 5, 1815 with such force that the noise could be heard on Sumatra, some 2,600km distant. A vertical column of ash debris reached a height of 45km into the atmosphere with the ash falling out up to 1,300km away. Pumice rafts up to 5km in length floated on the sea, and tsunami surges up to four metres high struck the Indonesian archipelago.

Mount Tambora is seen in this image taken by the Nasa Expedition 20 crew.

Alfred Russel Wallace, writing 54 years after the eruption, recorded that 12,000 lives were lost and “the ashes darkened the air and fell thickly upon the earth and sea for 300 miles around”. For the next four years after the major eruption, aftershocks occurred and it was estimated that 100 cubic km of pyroclastic material was ejected, weighing approximately 10 billion tonnes! Nitrous gases were emitted and Borneo was plastered in volcanic ash to a depth of one centimetre. Mount Tambora literally blew its top with its peak 66 per cent lower after the eruption – so great was the destruction of that mountain.

1816 – The year without a summer

One year after Tambora’s eruption, the winter of 1816 saw average global temperatures drop by 0.4 to 0.7 degrees Centigrade. Some authors have named 1816 as Poverty Year, for major food shortages occurred in the northern hemisphere. The latter were due to massive quantities of sulphur dioxide in the stratosphere resulting in a persistent dry fog along the Northeast seaboard states of the USA. It was referred to as a ‘stratospheric sulphate aerosol veil’.

In June 1816, frosts and snowfalls were reported in some of these states. Such conditions existed for three months and ruined agricultural crops. Heavy rainfall and cooler temperatures caused wheat, oats, and potato harvests to fail in the UK and Eire. Similar crop failures were reported throughout Western Europe, all related to this climate anomaly. Escalating grain prices and the increase in food costs in general led to riots in France and Germany. The worst ever wine harvests were recorded in those two countries in that very year.

Neither did Asia escape damage. In China, tree-crops, rice crops, and even water buffalo were killed by the unseasonal cold weather. The Yangtze Valley saw extreme flooding and in India, late torrential monsoon rain promoted the spread of cholera and lung infections.

Such events were occasioned by a build-up of atmospheric dust resulting from a series of five preceding volcanic eruptions, between 1808 and 1814, before that of Tambora’s. This caused the fall in temperatures worldwide as less sunlight was able penetrate the stratosphere. The accumulation of volcanic ash in the atmosphere resulted in unusually vivid sunsets. For the next few years after Tambora’s eruption, the famous English landscape painter, Joseph M Turner, coloured the skies in his oil paintings in yellowish tinges. The volcanic dust not only cooled the earth but scattered the light, filtering out the blues in the low sun, thus dramatically colouring the sunsets.

Human and environmental losses

Mount Tambora’s 1815 eruption actually caused the loss of 10,000 lives on Sumbawa through pyroclastic flows with another 18,000 people starving to death on the islands as crops were severely burnt or smothered in a thick, dense layer of volcanic ash to a depth of 100 centimetres within 75km of the eruption. It is thought that Tambora emitted hydrogen chloride and this combined with rain resulted in acidic rain destroying the food crops. Various estimates of the total loss of life, caused by this eruption, range from 61,000 to 88,000 people. Very little has been recorded on the loss of animal and natural plant life although AR Wallace briefly mentions the island as being devoid of vegetation.

Subsequent Indonesian volcanic eruptions

Certainly Krakatoa’s major explosion of 1883 sent volcanic ash high into the atmosphere for jet stream winds to transport around the world. This led to the most vivid red sunsets in the northern hemisphere where there was a slight lowering of the average global temperatures for a few years. A northern hemisphere summer temperature anomaly of minus 0.3 degrees Centigrade was recorded and is thought to have resulted in 36,000 deaths.

It will be interesting to see what effect the Anak Krakatoa, Lombok, and Sulawesi eruptions of 2018 and 2019 have had upon the world’s climate this year and in subsequent years. Perhaps they may only have had a marginal effect in blanketing out the sun for a short time. At the time of writing, it does seem that the UK and Europe have had exceptionally high spring and summer temperatures in 2019, far exceeding the temperature norms for these seasons.

Whilst world leaders are scratching their heads on how to reduce their country’s carbon dioxide and greenhouse gas emissions, volcanoes continue to erupt throwing their ash into the atmosphere and hence, as importantly, into the climate change equation. Where there is a will, there is a way to control manmade atmospheric pollution however Mother Nature remains law unto herself.