No, he's not doing more to tackle climate change than anyone on this planet. Let's say 25,000 sales in 2013 and 35,000 sales in 2014 [1]. That's 60,000 cars. Now let's take the numbers for electric GHG emissions vs. conventional emissions from this 2006 paper[2]. This is more of a reference, I'm not trying to say this paper is the unassailable truth. Also a disclaimer, these numbers will obviously be rough, again, just trying to paint a picture.
These numbers have 3 scenarios, all fairly optimistic:
Conventional (gasoline) emissions are 19.9 kg GHG emissions per 100 km.
1. Electricity is produced from renewables and nuclear
1a. Electric emissions are 0.343 kg/100km
2. 50% electricity from renewables, and 50% from natural gas with a 40% efficiency
2a. Electric emissions are 5.21 kg/100km
3. All electricity from natural gas with a 40% efficiency
3a. Electric emissions are 10.1kg/100km
At this point, I should note that burning natural gas has roughly half the emissions associated with burning coal in terms of CO2 equivalency.
Let's run with the middle scenario, which is still totally not representative of the country as a whole[3]. And we need some mileage, thankfully there are statistics on that. I'll use the 35-54 age group, which I'm guessing are the most likely to own Teslas, so 15,291 miles a year[4], which becomes 24,608km.
Aright, so we have 60,000 electric cars that we're gonna assume are straight-up replacing 60,000 conventional cars. Each car would replace 14.69(24608/100) = 3614.9152kg/year(60,000 cars) = 216,894,912kg. This is the annual grossly simplified reduction in emissions of replacing 60k conventional cars (using numbers from that paper for what a conventional car means) based on that idealized generation mix.
In 2012, our emissions were 6,526 million metric tons of CO2 equivalent[5]. Scaled down to our kilograms, it becomes 6,526,000,000,000kg. That amount displaced up above would account for 0.00332% of total emissions in 2012 based on those numbers.
For some other perspective, Ford F-series sales have been up significantly the past two years[6] post-ish recession, and 16 mpg seems like a reasonable average for that line of vehicles[7].
More perspective, the MIT study "The Future of Coal"[8] pegged an average 500MW coal plant as producing 3 million tons of CO2 a year (although it ranged up to 4.5 or so million tons in other literature). That presents a range of 2,722,000,000 - 4,082,000,000 kg. Although not all of that is necessarily emitted in every case. So, displacing one 500MW coal plant with say, a large wind farm, would displace 12.5x what those 60k cars would do annually.
Basically, what I'm getting at is that researchers and policy makers involved with utilities, DOE initiatives, and state governments (via RPS, no overarching federal clean energy policy[although the PTC obviously has a huge effect]) are probably all doing more to tackle climate change than Elon Musk. Not to crap on him, I would love to own a Tesla, I just like energy topics.
Links 2 and 8 are pdfs.
[1] http://en.wikipedia.org/wiki/Tesla_Motors#Model_S
[2] https://facultystaff.richmond.edu/~sabrash/110/Chem%20110%20...
[3] http://www.eia.gov/electricity/data/browser/#/topic/0?agg=2,...
[4] http://www.fhwa.dot.gov/ohim/onh00/bar8.htm
[5] http://www.epa.gov/climatechange/ghgemissions/sources.html
[7] http://www.fuelly.com/car/ford/f-150
[8] http://web.mit.edu/coal/The_Future_of_Coal.pdf