There have been a number of recorded incidences of "killer clouds" recently, yet when one looks at them in detail these articles appear to have little in common in terms of the chemical reasoning or content. Therefore, if one follows this thought to its logical conclusion there is no defining characteristic linking killer clouds save for the fact that they are "clouds." Let us look at a couple of examples.
1783 Icelandic volcanic explosion
In 1783 Iceland, which is one of the most active volcanic areas of the world, experienced an eruption from Laki Volcano, which lasted for well over four months, producing a fog-like cloud which, at one time or another affected most of Europe, drifting over areas such as Poland and the UK. Records available show that, in the UK alone, this cloud was responsible for the deaths of over 23,000 people. This can be evidenced by the local death records of the time, which showed that in many cities, towns and villages deaths during this period were often more than twice the normal average for similar annual periods.
What made these clouds so dangerous were their contents, which included sulphur dioxide and fluorine gases, substances which are dangerous for both humans and animals. In terms of the latter, it is suggested that thousands of the deaths in Iceland during this eruption resulted from people consuming animal products that had been contaminated because these animals eating contaminated grass. The direct effect the cloud had on people was irritations to eyes, ears, nose and throats and, due to the sulphuric acid and fluorine poisoning content this often led to death, especially for those who worked outdoors.
1986 Cameroon lake cloud
Another killer cloud phenomenon occurred in 1986 in and around lake Nyros, which is located in Cameroon. In this incidence, approaching two thousand people died virtually overnight, seemingly without explanation. It was only after detailed scientific examination was performed that it was discovered that the cause was related to an escape of a cloud of neat CO2 gases from the lake. Although water can absorb CO2, there is a limit to the safe absorption level, which are located in the deeper areas, especially when the water is in a confined area such as a lake. When that point is reached, CO2 is pushed into upper levels, where it is less secure. The slightest disruption at this level causes the CO2 to bubble up to the surface, where is escapes as a cloud of gas. As CO2 is heavier than air, which of course we need to breath, in sufficiently large quantities it will make breathing impossible. According to the scientists, those quantities can start as low as a 10% concentration to become fatal.
In an attempt to resolve the problem at Lake Nyros the scientists have lowered a pump into the lake, which is intended to release the CO2 in a more controlled manner. However, with the levels of this gas still high within the lake, there is no guarantee that this will stop a future occurance.
Although killer clouds can be manmade, to the extent that man can release poisonous gases into the air, as has occurred with bio-chemical warfare in the past, the natural killer cloud phenomenon described above are more concerning. Despite the fact that scientists are trying to find methods to deal with future incidences like those that occurred in Cameroon, there is the potential for such an incident to be repeated elsewhere. Some people have even raised the concern about the levels of C)2 in the oceans and what would happen if there was a major leak of CO2 from this source. Although scientists believe that this is unlikely, no one can be certain that it will not occur.
Similarly, in both cases the control of these events is outside the ability of man. The only difference that we can make is to continue our efforts to reduce emissions of CO2, and increase our scientific knowledge, which it is hoped may serve to reduce the human and animal costs of such disasters.