BANGKOK -- Hideki Sawano has attended many farewell parties recently. His team had 20 carbon traders in 2008; today, there are only seven. Working with Japanese trade giant Sumitomo Corp., Sawano buys carbon credits from Asia and sells them to European emitters. But as the demand for the credits shrank, so did the size of his team. Such market shrinkage can happen to businesses worldwide, but Asian traders like Sawano have felt this blow most sharply. They were the top traders in an international carbon emissions offset mechanism that once sustained a multibillion-dollar market, but lately, it seems to have lost its once-magical powers.