Why might the Bank of Canada decide to raise the overnight rate in 2015?

At the end of 2009, the unemployment rate was 8.3 percent, the inflation rate was 0.8 percent, and the overnight loans rate target was 0.25 percent. In mid- 2014, the unemployment rate was about 7 percent, the inflation rate was 2.1 percent, and the overnight loans rate target was 1 percent.