Assuming that manmade CO2 emissions are causing a rise in the Earth's temperature (a fact that is the subject of considerable debate in the scientific community), increasing CAFE standards will do little if anything to solve the problem. U.S. motor vehicles subject to CAFE standards account for 1.5 percent of global manmade greenhouse gas. The Environmental Protection Agency has confirmed that a 40 percent increase in CAFE standards would yield a maximum improvement in worldwide greenhouse gases of less than one-half of one percent. In the real world, raising fuel economy standards would not even approach these savings. Studies show that consumers are likely to drive more as the cost per mile of driving decreases and they hold on to their older, less fuel efficient vehicles longer as new car prices increase. The National Academy of Sciences concluded that substantial CAFE increases would cause the price of new vehicles to rise as much as $2,750 and force significant trade-offs for consumers.