When you think that CO2 only makes up .04% of the atmosphere and IF man is responsible for 3% of that .04% - it's really not much at all.
I don't think we can argue with the fact that climate has changed over the last 150 years, but it has always changed and always will. There are short cycles and long cycles effecting our planet. Solar activity is cyclic with short cycles of 11 and 22 years and has a direct effect on our climate. Our magnetic pole shifts all the time
The El Nino events in the southern oceans cause real short term climate change - they have been occurring for thousands of years. The scientist can't predict when they will appear, how long they will last or how severe they will be. The earth's orbit round the sun is not circular, it's on a 2,000 year cycle. Vikings settled East and West Greenland 1,000 years ago. Romans cultivated Vinyards in Britain 1,500 years ago.
On the other hand - if your life's work is funded by research into climate change, you need to keep the cash coming in.