The phrase "a natural explanation" is correct and usable in written English.
It can be used when discussing reasons or justifications that are based on natural phenomena or processes.
Example: "The scientists provided a natural explanation for the unusual behavior of the animals during the storm."
Alternatives: "a logical explanation" or "a scientific explanation".
A natural explanation is almost certainly the case here too.
Crucially, these irrepressible fluctuations provide a natural explanation for the temperature fluctuations observed by Planck.
As a scientist, you always go in a little bit biased, expecting there to be a natural explanation.
One of the challenges facing fundamental physics has been to provide a natural explanation for these three generations.
It was Darwin's genius that he provided a natural explanation for the organization and functional design of living beings.
Perhaps, after all the excitement died down, scientists did indeed discover a "natural explanation" of the sort Clarke warily acknowledged, and everyone dropped the matter.
While terrorism had at first seemed a natural explanation to many people in the chamber, Miller said that the possibility had never crossed his mind.
A professor of oceanography at Florida State University, he conducted an inquiry and found what might be a natural explanation: ice.
Fermat's principle and its application to focusing by mirrors and lenses finds a natural explanation in the wave theory of light (see light: Basic concepts of wave theory).
That lack of gratitude was, apparently, what she considered a natural explanation for her husband berating a boy who had a hard time at home and was in a strange hotel in another state.
In a world of miracles, none of which was so clearly miraculous that it would be irrational to claim there was a natural explanation, reason would lead us to the false conclusion that no miracles had ever occurred.
