Land-based measures of temperature covers 30% of the global surface. These recorders are poorly sited, affected by UHI effects (urban heat islands), and the only source of rising temperature measurements. Be skeptical of all the IPCC global warming hype:

http://townhall.com/columnists/peterferrara/2011/12/06/salvaging_the_mythology_of_manca...

Be very skeptical of computer models for air temperature, which do not take everything around the Earth into account. Do these folks really know what they are studying?:

http://www.scientificamerican.com/article.cfm?id=three-quarters-of-climate