Bloomberg: Japan is defending itself against criticism that it is exploiting a surplus of assigned emission credits and buying "hot air." The Japanese government and its largest companies plan to buy more than 350 million tons of emission credits in the five years ending in 2012, said Keiji Hisata, an official in Tokyo’s Kyoto Mechanisms Office at the Ministry of Economy, Trade and Industry. The purchase may include units assigned to the 37 countries with targets under the 1997 Kyoto Protocol, …