Methane hydrates are essentially frozen methane held on the seabed by a combination of low temperatures and deep water pressure. If the water warms, the methane can be released and bubble to the surface and there are vast quantities held there, sufficient to change the climate rapidly, so it is of considerable concern.
Previous scientific analysis has said that the chances of this happening are remote and up to now there has been little research in the area.
In a shortened version, the East Siberian continental shelf is very shallow and is normally frozen over and very cold and so it has held the methane hydrates safely on the sea bed.
The new situation is that the sea ice has melted for long periods in the summer and raised the temperature 7C and this is sufficient to melt the methane and release it to the surface.
Something to watch closely and no doubt there will be more research ships in the region next summer.