Check out the second adword down in this picture.
I don't live in New York. I live in Washington, DC, and Google adwords allows for very easy geotargeting. That means this is either a national buy roping in climate change voters or a buy targeted at decision-makers in DC. In other words, learn about Bloomberg on the environment, if you're concerned about climate change.
Let's see how widespread this buy is. If you have a moment, would you google 'climate change' and let us know in the comments if you see the Bloomberg ad. Do this a few times, as adwords rotates ads in and out. Also, leave your location so we can learn a bit more about who Bloomberg is talking to.
UPDATE: This is getting more interesting. People are seeing ads in St Louis, upstate New York, North Carolina, New Orleans, etc. They are not seeing ads in Canada. So what it sounds like is that this is a national ad purchase, explicitly. I thought it was possible that the ad buyer was lazy and just bought the adword 'climate change' generically across Google, but that doesn't seem to be the case. It's specifically in the US, or at least that's what the indications are. This looks like a national ad buy.
Update 2 (Chris): Relevant to this post, three weeks ago a friend of mine participated in a telephone poll conducted by Mountain West Research Strategies. Apparently, they asked many questions about his outlook on the two political parties, but the only politician they asked about was Michael Bloomberg. It should be noted that Mountain West Research Strategies was a polling firm used by Joe Lieberman in 2006.
Update 3 (Adam): Looking through a post of Chris' just now, Bloomberg also bought "Mike on nonpartisanship" adwords, which showed up in the Google ads on our site. Has anyone else seen other adwords buy relating to other issues?