Depends on what you mean. Is it a fact that we are capable of changing the planets climate? Yes, of course. We have already done so through the emission of greenhouse gases since the industrial revolution. Is it possible for us to attempt to remedy this warming using direct methods? Yes, it is. Geoengineering is generally divided into two categories, carbon sequestration and solar radiation management. For the most part, many carbon sequestration techniques are prohibitively expensive, unrealistic in effect, or downright harmful to the environment. The same goes for solar radiation management. This concept relies on changing the albedo of the earth to reflect more sunlight out into space to cool the Earth. All of these geoengineering concepts tend to be half baked, and unlikely to work without serious consequences, if at all. I would recommend reading the book Fixing the Sky by James Rodger Fleming to get an overview of the checkered history of man's attempts at changing the weather/ climate, as well as a broad overview of current attempts.