We can, to a point.
The science is quite clear that we are cumulatively warming our planet through our emissions of greenhouse gases. However, natural variation also exists. For example, in the 2008 climate report summary on the GISS (Goddard Institute of Space Studies) website, Dr. James Hansen of NASA attributed the slightly cooler global temperatures observed in 2008 to reduced solar activity.
At present, our GHG forcing tends to dominate, because most other forcing vary quasi-randomly. The GHGs, by contrast, just keep accumulating, year on year.
But as Monique and Bob say, we can find ways to change our cumulative carbon footprint for the better. And the latest science says that doing so can still be highly effective in avoiding the worst dangers forecast for the coming century.