a. There is no data to support global warming- this is not true, there is plenty of data!
b. Global climate is complex, so changes in global climate are hard to predict.
- I think that this is the best answer!
c. Increased levels of carbon dioxide are offset by other changes. -no, I don't think this is correct
d. There has been a decrease of extreme weather. -this is not true, there has been an increase in extreme weather, not decrease