Carbondioxide, being a green house gas has the property of trapping the heat from the sunlight and thus increasing the temperature of the place. As more and more rain forests are cut down and burned, there is an increase in this green house gas in the atmosphere thus leading to a steady increase in the temperatures.
As we look at the graphs that are given, we can see that the graph C shows the steady increase in the temperature as the time passes. Hence option C is the right answer