My main argument is in the title of this opinion. Despite what many people with very limited scientific knowledge believe, it is a fact that the overall consensus from the scientific community, supports that humanity is mainly responsible for the warming of the global climate.
Arguments that counter every myth denying Global Warming can also be found here http://grist.org/series/skeptics/
Personally I believe that there is such heavy resistance to Global Warming because people have a tendency to always deny imminent catastrophe. This is often justified as seen with the doomsday predictions made for 2000 and 2012. People simply do NOT want to accept that this is a very great threat to humanity and that we, the humans, are causing it.
From the 1940s to around 1970, the world cooled by a fraction of a degree. From around 1970 to 1998, the world warmed by 1 degree. Since 1998, we have had a minute decrease in temperature. Throughout all of these periods, people continued to pollute. The CO2 level in the atmosphere rose exponential during periods of temperature decrease, as well as periods of warming.
Just last week, a co-founder of Greenpeace testified that there is "no evidence of man-made global warming." In the late 60s, many scientists feared that there would be a man-made ice age. A generation later, the scientific community was warning us about an apocalyptic rise in temperatures. Both of these inaccurate views were based on less than 30 years of climate change. By examining data from many decades, scientists with the International Climate Convention realized that the temperature fluctuations every 25 to 30 years are completely natural.