Although the airspace is now open again, it has been impossible to be in the UK this week and not hear about, talk about or watch volcanoes. It has also made everybody painfully aware of the fact that we are totally and utterly dependent on air travel and that having a global air travel hub on a small island presents a further set of complications when the system doesn’t function as it should. Not only have travelers been stranded, but the impact was quickly felt by the likes of Kenyan flower growers and market gardeners – although this was apparently solved fairly rapidly as air freight was diverted to Spain and supermarkets trucked from there.

Arguably we have been really unlucky – a combination of location (near major air routes), timing (end of Easter vacation) and weather patterns (a huge blocking high pressure system) has made this event particularly traumatic for those directly impacted. But for those of us in London with no travel plans, the reverse has been true – nice weather, much less traffic near Heathrow and quiet skies. Even BAA, the company which owns and operates Heathrow has had its own small silver lining in this cloud of ash – apparently they have used the time to collect baseline environmental data around Heathrow which will help them better understand the local impact of aviation.

As readers of climate literature will doubtless know, volcanoes have figured heavily in global climate over the millennia. There is evidence in the paleoclimate  record that they may have contributed so much CO2 to the atmosphere in periods of extended high activity that warming occurred as a result. On a shorter timescale they also contribute to cooling of the atmosphere due to the discharge of large amounts of ash and sulphur compounds.

Whilst the current eruption is turning out to be very disruptive, compared to other eruptions in history it is a mere puff of smoke. Eyjafjallajokull has ejected about 140 million cubic metres of material, but Pinatubo (the Philippines in 1991) ejected 10 cubic kilometres – that’s 100 times as much and Tamboro in Indonesia ejected 160 cubic kilometers in April 1815. The super-volcano which still exists under Yellowstone National Park has the potential to eject at least an order of magnitude more than this – but with no expectation that it will do so anytime soon.

Even in recently recorded history there is evidence of the short term climate effects of volcanic eruptions. 1816, the year after Tamboro, was known as the “year without a summer” in Europe and another Icelandic volcano that erupted in 1783-1784 apparently impacted life in Northern Europe, parts of Asia and Africa and in Iceland killed over half of livestock followed by a famine in which a quarter of the population died. In the following years there were crop failures and record grain prices in France (this may of course be unrelated). Looking at the UK monthly temperature record for the past 400 years it is possible to see some of this (but there are also plenty of years with anomalous data in which there was no volcanic activity). The chart below shows yearly data from 1650, with the blue data being the annual average temperature, the yellow data being the maximum monthly average for a given year and the purple data the minimum monthly average for that year. The trend lines show the current warming and give some hint of the Maunder Minimum in the second half of the 17th Century.

Looking at the Tamboro event more specifically, the chart below shows the monthly average temperature as a difference to the average for that month for the period 1650 to 2008. 1816 does appear to be well below the average and is generally lower than the surrounding years.

In terms of CO2 impact, the grounding of thousands of flights has led to some newspapers here in the UK commenting on the CO2 impact. The Times calculated that some 1.5 million tonnes of CO2 emissions had been avoided (based on the premise that on a normal day the 28,000 flights in European airspace emit about 560,000 tonnes of CO2). This led me to wonder why they hadn’t included the CO2 impact of the volcano itself – there seem to be a number of different figures for this but all are less than the CO2 impact of European aviation itself and some considerably less.

 Meanwhile, con-trails are again visible over London and that almost ever present background noise has returned.

David Hone is Climate Change Advisor for Royal Dutch Shell

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