2) Climate scientists are just honestly wrong
Sometimes they are. No different than any other human being on the planet, including you and me both.
However, that brings up an important point. Just because people can be wrong from time to time, some more often than others, doesn't mean the consensus on AGW is wrong. The more people involved and checking the data and the conclusions, the less likely for any glaring completely wrong conclusions though. Not impossible, but certainly less likely.
One thing I fought long and hard about was for people to understand the mistake being made about forests. Forests have a reason for being. Many reasons actually. But as a general rule most forests are carbon neutral long term. That is to say their benefit is in the short carbon cycle, not so much the long carbon cycle that affects climate. The long cycle with regard to terrestrial systems is the soil. And particularly the soils under grasslands, not forests. Any soil scientist will confirm this. It is easy to look up and confirm for yourself as well.
Mollisols form in semi-arid to semi-humid areas, typically under a grassland cover....Mollisols have deep, high organic matter, nutrient-enriched surface soil (A horizon), typically between 60–80 cm in depth. This fertile surface horizon, known as a mollic epipedon, is the defining diagnostic feature of Mollisols.
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Of course Mollic soils are just one of many soil types, but as a general rule, this and others like Chernozem that are of major agricultural importance formed under grassland not forests, and have much deeper and much higher carbon content than the majority of forest soils. And soil carbon undisturbed is actually the long cycle in most cases.
Yet as well understood as this is, you still find many climate scientists making the same mistake the IPCC made here:
However, human activities, primarily the burning of fossil fuels and clearing of forests, have greatly intensified the natural greenhouse effect, causing global warming.
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They should know that the real problem with regards to AGW is the deterioration of those fertile grasslands. The long term carbon effect of forests is close to carbon neutral and the soils under them generally contain far less carbon.
