This conclusion is based entirely upon Hansen's own NASA/GISS ("gisstemp") data of surface measurements without adequate coverage of the poles and much of the oceans (which are extrapolated from temperatures up to thousands of miles away) and which have repeatedly been shown to be inappropriately "adjusted" and biased by urban heat island effects. Furthermore, NASA has admitted in climategate emails that their data is inferior to and partly based upon the other global surface temperature data from the infamous Phil Jones ("Hadcrut" data), who has admitted he's not so good at record keeping.
The other global temperature records are the 2 satellite records ("RSS" and "UAH"), which have much more complete coverage of the earth and generally track each other closely. Now lets compare what each of these data sets have shown since the 1998 El Nino (the only time during the past 12 years all 4 data sets were in close agreement). Hansen's data is shown in red at the top as the only global data set which can "claim" "record high global temperature ...in 2010." All three of the other data sets show cooling since the 1998 El Nino, a phenomenon completely unexpected from the computer models of the "greenhouse" effect.
Hansen's paper admits (top of p. 20) that they "have not yet attempted to integrate" satellite data into their global data set [Hmmm wonder why?]. Which data do you believe - that of ideologue James Hansen, who wants to rid the world of industrial civilization, or that of both satellites, or even Phil Jones?