Using vague language about scientific facts misleads readers
Anyone can do a simple experiment. Navigate to a search engine that offers suggested completions for what you type, and start typing "scientists believe." When I did it, I got suggestions about the origin of whales, the evolution of animals, the root cause of narcolepsy, and more. The search results contained a long list of topics, like "How scientists believe the loss of Arctic sea ice will impact US weather patterns" or "Scientists believe Moon is 40 million years older than first thought."
What do these all have in common? They're misleading, at least in terms of how most people understand the word "believe." In all these examples, scientists have become convinced via compelling evidence; these are more than just hunches or emotional compulsions. Given that difference, using "believe" isn't really an accurate description. Yet all these examples come from searching Google News, and so are likely to come from journalistic outlets that care about accuracy.
Does the difference matter? A recent study suggests that it does. People who were shown headlines that used subjective verbs like "believe" tended to view the issue being described as a matter of opinion-even if that issue was solidly grounded in fact.