1) Climate is an extremely complicated phenomenon 2) It is extremely difficult to model beyond a limited time frame. 3) The models we have, running on the most powerful, purpose built, computers rely on massive aggregations because there are otherwise too many interactions to handle. These aggregations are too large to be reasonably interpreted. 4) There is a large industry of well paid scientists, researchers, and policymakers who have built careers on Climate Change. Alarming news keeps them in a job, so they have an incentive to bias towards worst case outcomes. " It is difficult to get a man to understand something when his salary depends upon his not understanding it." - Upton Sinclair 5. Efficient and clean technology is worthy of pursuing regardless of its climate impacts. We can do more for the planet creating market based solutions in those directions than trying to manage CO2 directly.
Finally, I must acknowledge the Yale paper and climate scientists who have criticized his work. Rather than fire from the bushes, they should debate Koonin directly. He isn't a Fox News kook, if anything his credentials are superior to theirs.
Remember, one of the oldest ruse of charlatans is promising they can change the weather.