A number of scientists are emphasizing the tremendous challenges that will soon be faced when the depletion of fossil fuel supplies coincides with an alarming increase in the global population. They highlight agriculture which is heavily dependent not only on gasoline to fuel machinery but also on the petrochemicals necessary to manufacture synthetic fertilizers and pesticides. Without these petrochemicals, crop yields （作物产量）would be only a fraction of what they are today. To assume that an abundant source of renewable energy will address this challenge is to ignore the vital non-fuel uses of petrochemicals.

Then there is the challenge posed to the current levels of mobility. As a fuel, gasoline is unrivalled （无与伦比的）in its portability (轻便，可移植性). Electricity requires bulky （庞大的） batteries and hydrogen is notoriously（臭名昭著地） difficult to store. Biofuels might seem like an alternative, but the energy consumed （消耗的） when converting corn（玉米） into bioethanol（生物乙醇）, for instance, greatly exceeds the output when the fuel is utilized. In any case, once we reach a crisis in the food supply （粮食供应危机）, it will not make sense to divert food crops to other uses.

Although there seems to be a widespread belief that the era of oil dependency is coming to an end due to some technological remedy（改进）, this may be mistaken. Relying on such an assumption can lead to complacency（自满） and a failure to take precautions（预防措施）. Experts may not be able to come up with solutions that can lead to a pain-free transition（转变）. Scientists warn that relying on alternative resources might only support half of the global population. The absence of realistic alternative to fossil fuels will mean that the first priority （首要任务）will be to curb（控制） the demand for food.

Petrochemicals are used to manufacture pesticides, which are important for agriculture.

There is a widespread belief that the era of oil dependency is coming to an end.

As fossil fuels become depleted, there may not be enough food for the growing population.