First of all, climate change is happening. Whether it be man-made or natural is the real debate, but first let's look at some statistics from NASA. Greenland ice loss doubled between 1996 and 2005. 9 of the 10 hottest years on record have occurred since 2000. It becomes clear that climate change is happening. Now, are humans causing it? Let's look at some more statistics. Carbon dioxide levels in the air are at their highest in 650,000 years. We all know greenhouse gases trap heat on Earth. So, with more CO2 released into the atmosphere comes more heat. Also, for anyone wondering if it could be caused by a natural cycle, the Earth is actually no longer in the natural cycle. We have largely departed from the natural course of climate and there is no natural mechanism that explains it. Humans are ultimately the main cause of climate change.
During WW2 there has been enormous industrialisation taking place across the world to aid the war efforts and yet the rate of global warning was proved to be declining during that period. Additionally we know that climate has changed before in history and humans had nothing to do with it.
The climate has always been changing and always will. But the human influence is the one we can change. Also all the effects in nature might nearly cancel each other out, in which case the human factor is very strong.
More importantly our effect on the environment is very strong, look at China where smog is severely affecting their health. There's plenty of reasons to reduce our consumption of natural resources and how badly we poison our environment.