A THESIS: While climbing at a fairly steep angle in attempting to over-fly a huge thundercloud ahead (for which the captain had already requested  permission) the Air Asia plane, flying from Surabaya to Singapore in the early morning of  28 December 2014, entered the thundercloud, which, unknown to the pilots and air controllers, may have contained carbon dioxide (and/or ash) originating from a small volcanic activity on one of the islands in the vicinity.
Carbon dioxide can escape from the earth’s crust relatively undetected, rise in the atmosphere and accumulate in a relatively small area of the upper atmosphere.
Without oxygen all combustion stops, including jet-engines. Air Asia flight QZ8501, a twin engine Airbus 320, unfortunately flew into such a bubble of CO2. Both engines failed at about the same time. A source said radar data appeared to show the aircraft made an « unbelievably » steep climb, from 32,000 to 38,000 feet, possibly pushing it beyond the Airbus A320’s limits? Due to the high altitude and steep angle of climb, the plane lost power causing it to stall and plummet into the Timor sea.
The CO2 escaping from an unknown source in the earth’s crust may have been just enough to stall this particular flight, after which, due to high winds at this altitude, it was dispersed.
Two precedents are cited here:
Lake Nyos is a crater lake in northwest Cameroon, commonly known to have high levels of carbon dioxide. Under normal circumstances, these gases dissipate as the lake water turns over. At 9:30 p.m. on August 21, 1986, a cloudy mixture of carbon dioxide and water droplets rose violently from the Lake Nyos. As the lethal mist swept down adjacent valleys, it killed over 1,700 people, thousands of cattle, many birds and other animals. It is unknown what the trigger was – it may have been a landslide, small volcanic eruption, or even something as small as cold rain falling on an edge of the lake.
British Airways Flight 009 was a scheduled flight from London Heathrow to Auckland, New Zealand, with stops in Bombay, Kuala Lumpur and Melbourne. On 24 June 1982, the route was flown by a 4-engine 747-236B. The aircraft flew into a cloud of volcanic ash and carbon dioxide thrown up by the eruption of Mount Galunggung (approximately 180 kilometres  south-east of Jakarta, Indonesia), resulting in the failure of all four engines. The reason for the failure was not immediately apparent to the crew or air traffic control. The aircraft was able to glide far enough to exit the ash cloud, and all engines were restarted, allowing the aircraft to land safely at Jakarta airport.
There had been an eruption of the Mount Galunggung volcano southeast of Jakarta that day. Wind had blown a cloud of ash and carbon dioxide into the path of the plane. These do not show up on radar, hence remain undetected.
Conclusion: Only the flight recorder (black box) from Flight 8501 can disprove or otherwise validate this theory, one out of many possible explanations for the accident. The crucial point to look for is the relatively sudden loss of thrust due to failure of both engines at about 36,000 feet.
Investigation of possible volcanic activity in the region must also be carried out, to avoid any repeat of stalling aircraft, in case more CO2 is released.