The slowing of the great oceanic conveyor belts and the increased frequency of burn events in the tundra biome are evidence that __________.

A) The world is increasing its risk towards reaching some tipping point in the global climate system
B) The flux of methane has decreased
C) Solar radiation is warming the planet
D) There is nothing to worry about because these events have happened historically and are a part of Earth's natural climatic fluctuations