Airfare rates have increased substantially in the first half of this year, according to data compiled by American Express for its Business Travel Monitor, released yesterday. Rates are the highest they’ve been in two years, according to the report, based on capacity cuts and the fact that passengers are again traveling for business. International airfare is 8 percent higher than for the same time period last year, while U.S. domestic tickets are up by 9 percent, based on airfare paid by Amex clients. Hotel rates, however, have decreased, in large part due to the competitive negotiating environment last year for corporate rates. International and domestic rates paid both dropped by 2 percent from last year’s numbers at midyear.