...you also need the data. Setting up a denser sensor framework on land isn't difficult - it just costs more money. A big problem though, is getting a high enough data density from the areas covered by oceans, which is where most of the large weather systems form and build.

Why not just start up a new distributed computing project for a fraction of the cost? Lots of people love to volunteer computer time, especially if the project is 'cool'.

...that the people who decry global warming want to get bigger computers that generate more heat, use more fossil fuels, and thus cause the weather to change more. 

Scientist: "Let's power this thing on"
Computer: "Temperature in this city has risen .3 degrees, icecaps are melting"
Scientist: "Brilliant! This computer is saving our lives"