Why are there different theories about the effects of global warming?

a. There is no data to support global warming.

b. Global climate is complex, so changes in global climate are hard to predict.

c. Increased levels of carbon dioxide are offset by other changes.

d. There has been a decrease of extreme weather.

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