what fallacy can we find in this sentence?

“Belief in God has its origins in humanity’s desire to explain things that we did not understand, such as thunder, droughts, and solar eclipses. We now know that such phenomena have natural causes. Therefore belief in God is no longer needed and no longer justified.”

Belief in God has its origins in humanity’s desire to explain things that we did not understand, such as thunder, droughts, and solar eclipses.

insignificant cause mostly. If we conclude that belief in God is no longer needed or justified, we need to address all the reasons for belief, which is not practical. A better argument would be:

P1. Belief in God has its origins in humanity’s desire to explain things that we did not understand, such as thunder, droughts, and solar eclipses.

P2. We now know that such phenomena have natural causes. 

C. Therefore, belief in God as a result of our desire to explain things that we did not understand, such as thunder, droughts, and solar eclipses is no longer needed and no longer justified.

I would still have an issue with the ambiguity of "things we don't understand." Clearly, there are many things we don't understand like the origin of the universe and consciousness where premise #2 does not apply.

The entire argument is addressing a fallacious line of reasoning. The desire to explain things we don't understand may be a cognitive bias, but concluding that a God exists for this reason is a logical fallacy (argument from ignorance / God of the Gaps).

It seems to be a non-sequitur, for a few reasons.

Belief in God can be for other reasons too, unconnected with thunder, and the like.

Also, it is logically possible that God is the force/controller BEHIND all that we see as being "by nature."

That is the way some people think, even if it sounds ridiculous. 

Hi, hyunho cho!

         Include the straw man fallacy among the other two strong answers. Belief in God is not fairly represented as originating in a desire to explain particular celestial and weather events, or in fact any particular event. The “origin” of belief in God is not a straightforward legacy; different people in different eras believed in God for different reasons. 

         A stronger root within the history of belief in God—a root more fair to theism to attack—would be the natural theology of classical philosophers that followed upon their metaphysics. These were arguments that God is guaranteed to exist, given facts uncovered philosophically about the nature of reality. In Western Philosophy, natural theology originated as an inquiry into the necessary conditions of there being any motion whatever . In related but slightly different ways, Plato (considered by some scholars to be the first natural theologian in western philosophy) and Aristotle argued that in order for there to be any motion whatever, it was necessary that down the chain of causal activity there be something capable of imparting motion without itself needing motion imparted to it. God and the unmoved mover were conceived of as self-same and the classic theistic attributes were unpacked through consideration of what an unmoved mover would have to be like (a method called creation theology.)

         This was not an inquiry into the immediate causes of formerly poorly understood phenomena, like thunder or eclipses. Also, Plato and Aristotle were not giving arguments to the best explanation, or a scientific hypothesis, or a God of the gaps account. The arguments are about the metaphysical preconditions of motion as such,  not about this or that particular instance or species of motion around which, moreover, there is poor understanding. And the arguments were deductive moves from what they did profess to understand—the nature of motion. They reasoned deductively to a God because of how their metaphysical accounts of motion entail an unmoved mover as a precondition of the possibility of motion and as the ultimate source of any real instance of motion. 

         If a critic will attack a tradition far back in the history of thought on the existence of God, it is fairer to attack the steel man of the tradition of the argument from motion started by Plato and Aristotle, not the straw man about “whoa, where did that loud clap in the dark clouds come from?!” The argument from motion is still defended in the 21st century. 

Thank you, hyunho cho.

From Kaiden