The Nasa researchers, alongside a team from UCSB, made the comparison by looking at past tropical ocean surface temperatures.

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While this is a significant sum, to be sure, if an apples- to-apples comparison were made, the price of purchasing and operating modern fighter aircraft wings or a class of surface ships or submarines would significantly exceed that associated with a ground-based NMD system.

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"Even though on the surface you're looking at 35% versus 39.6%, it's a deceptive comparison, " says Robert W. Wood, a tax lawyer with Wood LLP in San Francisco.

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