If the science of climate change and global warming are this clear, why is there so much debate among politicians, scientists and pretty much, everyone?

The truth is that the Earth’s climate system is extremely complex and up to date there are still many doubts about how it functions.  Very powerful computers have been used to model the climate, but these models will probably never be 100% reliable or anywhere near.  So there is definitely room for some doubt.   But as you have seen, the science of climate change and global warming has matured a lot and thus nowadays most scientists believe that Global Warming caused by human activities is real.  Just check out this fragment of a Wikipedia article on the scientific opinion on climate change.

http://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change

Joint Science Academies Statement
In 2005, the national science academies of the G8 nations, plus Brazil, China and India, three of the largest emitters of greenhouse gases in the developing world, signed a statement on the global response to climate change.  The statement stresses that the scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action, and explicitly endorsed the IPCC consensus.
Some scientists believe that there is not enough data to believe that the recent rise in temperature in the Earth can be attributed to human emissions of greenhouse gases.  Others believe that Global Warming can be attributed to human activities, but remain greatly skeptical about how much.  Others believe that the role of CO2 in the atmosphere is certainly harmful, but that the climate is too complex to really predict in which ways it will be harmful.  There are many different kinds of doubts and questions that remain to be answered.  You can see some of them here, http://en.wikipedia.org/wiki/List_of_scientists_opposing_global_warming_consensus.  But as you can see, the majority of the scientific community believes that humans are indeed responsible for a great part of Global Warming.
It may seem impossible that humans can cause so much damage to something as big and strong as a planet.  But just take a look at what we have done to the ozone layer and how many species have become extinct or greatly endangered because of us.