"Grand conspiracy" refers to a belief or theory that a complex plot or secret agreement exists involving many individuals or groups working together to achieve a certain goal, typically to manipulate or control a situation or events. Full definition
I can't tell whether he is accusing the entire climatology profession of grand conspiracy or simply gross incompetance. (realclimate.org)
Religious leaders show passion for their beliefs and affirm their fears about grand conspiracies that are a sign of the end times. (nakedpastor.com)
I have no doubt that this gentleman honestly believes climate scientists (along with the feminazis and those who faked the moon landing, of course) to be part of this same grand conspiracy, too. (realclimate.org)