An international team of scientists has presented the first-ever evaluation of the impact of the 1816 eruption of the Tambora volcano in Indonesia on the Iberian Peninsula. Historical documents and observations by Spanish and Portuguese stations have shown that emissions of gas and particulates from the volcano limited the effect of solar radiation in Spain, where temperatures that summer did not rise above 15 C.

The Tambora volcano in Indonesia erupted in April 1815, but North America and Europe did not notice its effects until months later. In 1816, known as 'the year without a summer,' gases, ashes and dust arrived over the Iberian Peninsular and reached the stratosphere, where they remained long enough to create 'an enormous sun filter.'

These are the findings of a study by an international team, with Spanish participation, which have been published in the latest issue of the prestigious International Journal of Climatology.

The researchers have studied, for the first time, the impact of this atmospheric phenomenon on agricultural production in the Iberian Peninsula in 1816 and 1817, and have evaluated and compared the climate in the area with that in 1871-1900, before it started to be affected by climate change.

'The year 1816 was characterised by great anomalies, especially in the summer, which was much colder and wetter than usual. In Madrid, temperatures were below 15 C in July and August, and that Autumn the Catalan peaks of Montserrat and Montseny were covered with snow and the Llobregat river froze over,' Ricardo Garcia Herrera, one of the authors of the study and a researcher at the Complutense University of Madrid (UCM), tells SINC.

The study includes information from the first instrumental observations carried out on the Peninsula by scientists in Lisbon, Madrid, Barcelona and San Fernando de Cadiz. 'It also brings together Spanish and Portuguese documentary sources, such as private diaries (for example that of Baron Malda of Barcelona), which provide qualitative information about the weather, and religious documents including weather-related prayers,' adds Garcia Herrera.

Baron Malda wrote in his diary that the unusual temperatures in the summer of 1816 could have been related to a 'great snowfall' in the centre of Spain on July 16. He also pointed out that it 'was snowing considerably' in the Pyrenees and the north of Europe. According to the scientists, this information coincides with the low temperatures of 13.1 recorded that day in Madrid. The apparent snowfall mentioned by the Baron may in fact have been a hail storm.

The eruption of the Tambora volcano was probably 'the greatest recorded eruption in historical times' according to the researcher. This is demonstrated by its explosivity index (a measurement of the size of the eruption), which, at 7, 'was greater than any other more recent eruption, including that of Mt. Pinatubo in the Philippines,' the expert tells SINC.

The consequences of the eruption were noticed not only on the climate, but above all on agriculture. 'The low temperatures meant that many crops did not ripen, or if they did their yield was very little and very late,' says Garcia Herrera.

The decade from 1811 to 1820 was marked by serious socioeconomic impacts resulting from this poor agricultural production, with malnutrition and the increase of epidemics in Europe and Mediterranean countries. Low temperatures, freezing temperatures in Spring and heavy precipitation between 1816 and 1817 affected the growth of many crops very badly.

The cold and wet summer led to fruits being of poor quality, as well as vines and cereals ripening very slowly, which impacted on harvests. The climatic anomalies were more consistent in Lisbon and Cadiz, showing that the phenomenon in the Iberian Peninsula was not the same as in central Europe.

In addition to the UCM, the University of Extremadura, the University of Barcelona, the University of Lisbon (Portugal), the Lusophone University (Portugal), the Gabriel Pereira de Evora Secondary School (Portugal), and the University of Berne (Switzerland) also took part in the study.