I'm quite sure we have contributed to climate change but I have doubts that it is anywhere near the scales the climatologists claim.
It most certainly is and evidently is a problem. Even those who deny it admit that it is occurring, but say that it is natural and not because of man.
Another more imminent threat to mankind however, is the disappearance of bees, which will be causing a problem in the near future.
No it wont, that's just another exaggerated story. NewScientist debunked this myth:
The first tenet - that bees are responsible for the production of a large fraction of our food - is simply untrue. Pollinators are important for many crops, but it is a myth that humanity would starve without bees.
About 70 per cent of the 115 most productive crops, including most fruits and oilseeds, are animal-pollinated. These account for nearly 2.5 billion tonnes of food a year, about a third of global agricultural production. However, few of these crops depend on animal pollination completely, owing largely to their capacity for self-pollination
Source:
http://www.newscientist.com/article/mg20427316.800-the-truth-about-the-disappearing-honeybees.html