Two critical requirements must be met before light elements, like hydrogen or helium, will fuse and form heavier elements. the two requirements for nuclear fusion are

In order to achieve a nuclear fusion, one of the following requirements that must be attained are high temperature and high pressure.

High temperature - temperature must be 100 million degrees kelvin to a point that hydrogen already becomes plasma

High pressure - extremely high pressure is required so that the distance between hydrogen atoms must be at the required 1 picometer apart

Honestly "global warming" may be a slight possiblity, however they called it "climate change" because its not real, in fact we had one of our coldest days here not too long ago, and the "issues" with this subject is a blindfold for actual problems.