When the Church says that human life starts when the sperm penetrates the egg, and not when the pronuclei have fused, is that a Church pronouncement on science?
I’m not aware of any Church document that uses the biological terminology in the bolded portion above. What the Church does say is that life begins “at the moment of conception”. This is the terminology used in the Catechism of the Catholic Church and in other Church documents. Also in regard to Mary’s Immaculate Conception.
Does it require religious submission of will and intellect, or more?
I’m pretty sure that one must give submission of will and intellect to the teaching that human life begins at the moment of conception . But it would be best to check with a priest to be certain.
It does require “more” in the sense that it is a matter of grave sin to procure an abortion at any time after the moment of conception.
So my next question is, if this is a pronouncement on science
It’s not the Church making a pronouncement on science. Science actually shows that the Church teaching is accurate. It can now be seen that the fertilized ovum is living. The Church teaching has to do with the properties (not sure if that’s the correct word) of a human soul, and when a human soul is infused. The Church teaches that the human soul is infused by God at the moment of conception. Biological science doesn’t deal with “souls”.
Neither the Church nor scientists always knew just what took place in the womb. St. Thomas Aquinas accepted the current thinking at his time (a progression of souls in the womb: first a vegetative soul, then an animal soul, and finally a human soul). But even with man’s incomplete and inaccurate knowledge, the Church from the very beginning, and St. Thomas Aquinas also, forbade abortion.
then how does this differ from our obligation with regard to what the Pope has said on climate change?
I have not read the encyclical yet, so I’ll leave this to someone else. I’ll only say that it’s pretty obvious to most that a climate change is taking place.