Comparisons; public perception and risk

Comparison with impacts by Near Earth Objects (NEOs)

The recent concern in UK Government about NEOs impacting the Earth raises the question of whether super-eruptions are a comparable threat.

A large (1000 cubic kilometres of magma) super-eruption has been estimated (by Prof. Michael Rampino, New York University) as having comparable global effects to an object 1.5km in diameter impacting the Earth.

According to the recent report by the UK Task Force on Near Earth Objects, the best available estimates suggest that such impacts occur about 1 in every 400-500,000 years. The present estimate of recurrence rates for super-eruptions of this size is around 1 per 100,000 years. Thus, the probability of the Earth having a global-scale natural disaster from a super-eruption could be as much as 4-5 times greater than for a large impact.

Comparisons with nuclear war and radioactive nuclear waste

Study of large volcanic eruptions’ climatic effects was boosted during the 1980s by the issue of the potential long-term environmental effects of thermonuclear war. From this research, the concept of “nuclear winter” - pronounced cooling in the few years following the war - emerged. In a nuclear war, large amounts of dust and aerosol are injected into the atmosphere. Data from volcanic eruptions like Mount Pinatubo provided opportunities to later test “nuclear winter” models. It emerged that the main cause of disaster would be destruction of global agriculture and food supply. After a year of severely reduced food supply, there would be mass starvation.
Since a nuclear winter might last two or three years, scientists concluded that this could well threaten the survival of the human species. Casualties from the immediate consequences of nuclear winter due to direct destruction and radioactive contamination would be small compared with those due to mass starvation. This apocalyptic depiction of the consequences of nuclear war by the scientific community had a profound influence in governmental efforts to reduce the world’s nuclear arsenals and the threat of conflict.

The possibility that super-eruptions might have the same effects as nuclear war, by causing severe volcanic winters, is why this group wishes to draw attention to this natural volcanic phenomenon.

Public perception and risk

There are probably no greater problems for modern politicians and decision-makers than dealing with scientific uncertainty and perceptions of risk. A few years ago the UK Government banned the sale of beef-on-the-bone, based on an assessment of an exceedingly low risk. Politicians felt obliged to act more because of public risk perception than scientific evidence. Policy towards genetically modified food, biotechnology and nanotechnology has likewise been influenced by public perceptions of risk.

A comparison can be made between risk from nuclear waste and risk from super-eruptions. Here the interesting comparison is that both risks have to be viewed over geological time-scales.
Risk is commonly presented in terms of annualised probabilities of a fatality. So, for example, UK Nirex were required to demonstrate a risk of less than one in 100,000 fatalities to make a safety case for burying intermediate level nuclear waste near Sellafield. Further, the safety case had to be made over a 100,000-year period, because of the very long decay time of the radioactive waste.

In the same period of 100,000 years there are likely to be several super-eruptions. It is possible that each of these eruptions will affect many millions of people. Let us suppose, conservatively, that such an eruption directly or indirectly killed one million people. The annual probability of a significant super-eruption might only be 10-4 (1 in 10,000), but the consequence is ten million deaths.

Thus over 100,000 years it is likely that tens of millions of people will die because of super-eruptions, while a handful of people may die because of the storage of existing nuclear waste over the same time period (assuming that the required safety standards are met).

Of course, the huge time periods involved make such comparisons difficult. In the same long period considerable numbers of people will die from transport accidents. However, neither road nor airplane accidents, nor accidents with nuclear waste, are going to threaten civilisation and the global community. Enormous amounts of human effort and financial resources are allocated to the nuclear waste problem, which with existing technology is only likely to lead to a small number of deaths over a period 30 times longer than recorded human history. In contrast, natural events, which are inevitable and could even threaten civilisation, are currently not recognised as a problem.

Link to next section, Forecasting and potential effects of the next super-eruption