That's not what they do.
Only a few scientists predicted an ice age, who were found to have used faulty data. The majority redacted the claim. However, the overwhelming majority of scientists in the '70s predicted a rise in temperature, not a decline, and that assessment has been correct. Either way, scientists are able to make mistakes. The point of a scientist isn't to already know everything. The point is to research and discover, then report the discovery.
And they don't use 5-minute intervals to determine global warming. That's what you would probably do because you have no fucking clue what you're talking about. They use global data year-round to determine yearly averages and use literal decades worth of data to track the increase or decline. A 5-minute spike, as you put it, is completely irrelevant and if you knew what you were talking about, it wouldn't be something you'd bother bringing up.