This is no conspiracy nor is it a theory. Various advanced governments do in fact have technology capable of modifying weather. They even have capability to manipulate weather as a warfare device.
This is also in fact nothing new at all. The technology at minimum had to have been existent before 1976 AD. The reasoning is simple: the advanced nations signed a UN treaty barring use of "environment modification techniques" that have a detrimental effect on other nations that are party to the Enmod Treaty. With how the treaty is worded a powerful empire like America or Russia for example may use such techniques on their own countrieso r non-party nations to the treaty, but are forbidden from using such on other countries that have signed the Treaty.
Here is the text of the Enmod Treaty:
Show Treaty
Here is also an official list of the signatories and notes of "Reservations" and calls for more fleshed out definitions on some parts of the Enmod Treaty by party nations.
https://treaties.un.org/Pages/ViewDetails.aspx?src=IND&mtdsg_no=XXVI-1&chapter=26&lang=en
So this is one that is certainly no conspiracy nor a theory but is in fact reality as there is a tremendous paper trail, admissions, and evidences supporting the existence of Weather/Environment Modification. Additionally there is at minimum a reasonable expectation that some nations may possess so-called "Weather warfare" technology as per the fact they had to sign a treaty acknowledging the existence of such and promising not to use said technology on party nations to the treaty.