Final answer:
To evaluate the external costs of energy technology like a power plant's carbon emissions, collect data on pollution-related health impacts, environmental damages, and climate change economic effects. Compare these costs to the economic benefits to determine if they are 'too high.'
Step-by-step explanation:
When considering the internal and external costs of energy technologies, such as carbon emissions from a power plant, there are several factors to consider. Internal costs are those that the energy producer incurs directly, such as the cost of fuel, operation, and maintenance of the plant. External costs, on the other hand, refer to the costs that are not paid by the producer but by society and the environment, including but not limited to health impacts from air pollution, environmental degradation, and the negative effects of climate change.
To put a dollar value on the external costs of carbon emissions from a power plant, one would need to gather data on the health impacts due to pollution, the cost of environmental damage, and the economic impacts of climate change. In addition, to analyze a project like the Keystone XL, an economist would examine the environmental costs of potential oil spills against the economic benefits from the project and decide whether the external costs are "too high" when put in balance with those benefits.