The biggest concern with an eruption the size of Yellowstone is ashfall.
The force would shoot ash into the atmosphere up to 30 kilometres high where the easterly jetstream would carry it as far away as Europe within three days.
The volcano would also eject sulphuric acid into the air forming an aerosol that remains in the atmosphere for years, screening out sunlight, causing global temperatures to drop and killing crops for years afterward.
Even 1 millimeter of ash will close airports, cause damage to vehicles and houses, and contaminate water supplies.
SCIENTISTS have warned the world is in "volcano season" and there is up to a 10% chance of an eruption soon killing millions of people and devastating the planet.
The world's most dangerous active volcanoes include Yellowstone, Mount Vesuvius in Campagnia, Italy, and Popocatépetl i near Mexico City.
If any of them or other massive volcanic peaks suffered a major eruption the team said millions of people would die and earth’s atmosphere would be poisoned with ash and other toxins "beyond the imagination of anything man’s activity and global warming could do over 1,000 years.
The chance of such as eruption happening at one of the major volcanoes within 80 years is put at five to ten per cent by the experts.
There are already fears that Yellowstone could blow any time within the next years on a scale that would wiped out the western USA and affect the course of global history.
The report - “Extreme Geo-hazards: Reducing the Disaster Risk and Increasing Resilience,” warns global government's preparations for such happenings are virtually non-existent.
It said: "Although in the last few decades earthquakes have been the main cause of fatalities and damage, the main global risk is large volcanic eruptions that are less frequent but far more impactfull than the largest earthquakes.
“Due to their far-reaching effects on climate, food security, transportation, and supply chains, these events have the potential to trigger global disaster and catastrophe.
"The cost of response and the ability to respond to these events is beyond the financial and political capabilities of any individual country.”
Hence extreme volcanic eruptions pose a higher associated risk than all other natural hazards with similar recurrence periods, including asteroid impacts.
The report looked at other major geo-hazards facing the globe, including earthquakes, drought, asteroids floods, tsunamis, hurricanes, avalanches and wildfires.
Large earthquakes and tsunamis have happened more in the last 2,000 years, meaning there was better preparedness.
The report concluded: “Volcanic eruptions can have more severe impacts through atmospheric and climate effects and can lead to drastic problems in food and water security, as emphasized by the widespread famine and diseases that were rampant after the Laki 1783 and Tambora 1815 eruptions.
“Hence extreme volcanic eruptions pose a higher associated risk than all other natural hazards with similar recurrence periods, including asteroid impacts.”
The eruption of Tambora on Sumbawa, Indonesia killed about 100,000 people, but ash clouds meant there was no summer the following year and it was “one of the most important climatic and socially repercussive events of the last millennium,” the report said.
The earlier Icelandic event killed close to 10,000 instantly, but the long-term, effects wiped out 25% of the population and were felt across the planet.
A famine in Egypt reduced the population by one sixth, 25,000 died in the UK from breathing problems and there was worldwide extreme weather.
Similar scale events today would be much more catastrophic, the team warned, due to
much bigger populations, global travel and food chains and reliance on technology.
Worryingly, scientists say research over the last 300 years of volcanic activity shows we are currently in a "volcano season" meaning increased activity.
Volcanoes are also more likely from November to April in the northern hemisphere when ice, rain and snowfall can compress the bedrock.