Intriguing that the quote was about the old M&M paper.
The short answer would be: more data. A longer answer would go into the types of data: a lot of phenological indicators (as I've noted) -- quite a few things in the most recent IPCC report that might have gone unnoticed by those just reading the summary for policymakers -- some pithy comments by Frank Wentz I discovered by accident -- the summer sea ice trend -- and there's more, a lot more. I don't have three hours to write it all down.
I'd be curious to know what you think I was more skeptical about. I've felt that I always was consistent on increasing atmospheric CO2 concentrations causing warming, and hewing to a mid-range (2-3 C) projected global temperature increase by 2100. I credited the hockey stick critics with doing necessary work to address discrepancies in that line of research, while always seeing the paleoclimate research as only contributing to, and not defining, knowledge of how the modern climate is changing. Mann and Co. coming out with another paper that reignites the sound and fury is a distraction, because it creates emphasis on sidebar questions like "was the MWP actually warmer or only just as warm as now?" and "if it warmed up in the past naturally, then there's no proof that the warming now is non-natural, is there?" (Pardon me while I choke.)
As this discussion has progressed, I've become increasingly dismayed by the constant barrage of inaccurate, incorrect, and repetitively reiterated discredited and misunderstood arguments trotted out by the increasingly vocal skeptics, which are accepted credulously by those who view climate change solely as a political issue. My dismay has certainly affected my tone.
In your post above you appear to not have made up your mind and were skeptical about Mann’s claims. Today you just dismissed the MWP with a red herring counterargument and Mann’s continued attempts to localize the MWP to Greenland have gained your tacit approval (is Mann the distraction or Mann’s critics?) Mostly it’s your tone that has change partly from the continued repetition of old arguments, and partly from the hardening of your position in general. You were quite successful in countering Mars is warming and numerous other arguments made countless times. Now you have the impression that the denialists are switching arguments (a claim made over and over on RC), when you are only looking at the Rush Limbaugh arguments. The truth is that the skeptics and the AGW proponents have both stayed more or less consistent over the last decade but their idealogues have varied wildly (Mann’s changes in tactics being a perfect example).