The phrase "careless manner" means not paying attention or not being careful while doing something, which can lead to mistakes or accidents. Full definition
«If applied in a careless manner, war metaphors can delude our sense of what's possible therapeutically, and give false hope to people and caregivers who are suffering,» George said. (pennstatehealthnews.org)
to do or perform in a hasty or careless manner: to scamp work.» (indiekidsbooks.com)
While speaking about climate change in such a careless manner is both uninformed and irresponsible, for Brietbart News these statements are notable for their lack of direct climate change vitriol. (projectearth.us)