I am also skeptical of effects that appear out of data due to selection bias of the results reported or through other statistical artifacts. The idea of the null results from tobacco reminds me of the replication crisis in psychology and education research - results that are taken as conventional wisdom (learning styles etc.) that are non-existent; which is obviously an outcome we would all like to avoid - if it is non-existent. Another example would be the rate at which HIV is passed on through vaginal intercourse (very low chance) yet that information is not being publicly announced because people have a difficult time in assessing risk and this information would promote risky behaviour or the meme that alcohol destroys brain cells (incorrect) however debunking these myths publicly will likely cause significantly more harm than believing them. What about paper burning (for many Asian religions) and fireplaces producing particulates that are more dangerous than tobacco(https://www.samharris.org/blog/item/the-fireplace-delusion
It is always difficult to make blanket statements when the truth is often subtle and there will always be some data that contradicts the mainstream, it is then the task of the scientific community to create some metric to place a value on the data that is against expectations - the greening data seems to be important enough to at least be part of the mainstream conversation on climate change.
If scientists filter their results in a political way it then opens up accusation of politicised science (such as the CSIRO - "more religion than science" comment http://www.abc.net.au/news/2016-02-11/csiro-boss-larry-marshall-defends-controversial-shake-up/7157650
), which can cause even more tribalised thinking and less trust in the scientific process and the scientific community as a whole. Ridley is questioning the negative future effects of global warming and also discussing the possible positive impacts.
The idea that positive effects should be suppressed or not publicly spoken about will fuel the opposition to climate change. I suppose it comes down to how detrimental the rise in sea levels (and other associated negative effects) will be as opposed to the greening; the greening itself will have a dampening effect as well, for the same reason that methane is a greater greenhouse gas than CO2 because of the larger current concentration of CO2. It is a possible future that has an increase in agricultural production and a "greener" world as well as a world with higher sea levels that would be considered a better overall bargain for humanity and other organisms than the current state. For example if there was a 5% increase in global greening for every inch increase in sea levels it would not be clear to me that this would be a terrible outcome for the world.
I fully agree with a conservative and cautionary approach that would mean that I, personally, would be against tampering with the environment by adding CO2 even if the models predicted positive changes, however, such a positive future is possible and discussing it does not equate to promoting the emissions of CO2 or being a AGW denialist. The line of reasoning that appealed to me was that most systems have negative feedback loops built in and that positive feedback loops would indicate that the system was unstable. This negative feedback loop is demonstrated by the enhanced greening effect due to increased CO2 and more water (as temperature increases the humidity increases - so the rate of photosynthesis increases which will dampen further warming) - this data has also been published for decades yet does not often make it to public AGW discussion.
"The limited amount of available experimental data has as a trend that water use per unit soil surface area will change little (-10 to +10%). As, however, the general trend towards an improved water-use efficiency is clear, the productivity per unit of available water is expected to rise by 20-40%, probably much less than the value (100%) calculated from a reduced stomatal conductivity and an increased photosynthesis. Some studies show that in situations with marginal water availability the threshold for a successful crop may shift to lower values (Chaudhury et al., 1990,b; Clifford et al., 1993; Grashoff et al., 1994). Whether at otherwise unchanged water availability this would open up possibilities to reverse existing trends towards desertification in certain areas is very questionable, as apart from precipitation falling short to maintain existing vegetation, other aspects like over-exploitation might dominate. It should, however, be emphasized that present knowledge on feedback among vegetation characteristics, gas exchange and albedo and the regional climate is insufficient to draw firm conclusions." http://www.fao.org/docrep/w5183e/w5183e07.htm
Ridley mentions that he has moved away from being concerned about global warming to being cautious but optimistic about the future. He seems to be questioning the calculus of how detrimental the effects of global warming will be versus the current abatement costs. I would summarise Riley's views as:
1) Global warming exists (~0.85*C increase in global temperatures)
2) This warming is primarily due to human activity (so he would be considered a believer in AGW)
3) The negative consequences are exaggerated and the positive consequences are suppressed
Both 1) & 2) are mainstream positions and it is only 3) that is novel - I'm not sure if Riley denied temperature changes or had some other "idiotic denialist talking points" or moving the goal posts - are there any links or examples of this occurring? Regardless of his previous stances, his current position seems eminently reasonable and hopeful.