Final answer:
Under a "business-as-usual" scenario, average global temperatures are expected to increase by 3-4°C by 2100, which falls within the predicted range of 1.1°C to 6.4°C according to various climate models.
Step-by-step explanation:
According to a range of climate models, if humans continue on a "business-as-usual" scenario, whereby greenhouse gas emissions continue to grow without significant mitigation efforts, average global temperatures are expected to increase. The expected rise in temperature by the year 2100 varies based on different emission scenarios and climate model predictions. The most commonly cited figures suggest an increase of anywhere from 1.1°C to 6.4°C (about 2°F to 11.5°F), with some regions experiencing more significant changes than others.
Given the possibilities outlined by these models, the most appropriate answer to the student's question would be option b) 3-4°C, as it falls within the middle range of the predicted temperature increase scenarios if current trends continue unabated. It is important to note that the exact increase could be lower or higher than this, depending on how greenhouse gas emissions evolve over the coming decades.