The average surface temperature of earth . . . . . . . . more than 1 degree Fahrenheit since 1900.

In the given sentence "The average surface temperature of earth has increased more than 1 degree Fahrenheit since 1900," the most appropriate option to fill in the blank is "has increased."

The verb phrase "has increased" is in the present perfect tense, which is used to indicate an action that started in the past and is still relevant in the present. In this context, it expresses the ongoing impact of the increase in the average surface temperature of the Earth since 1900.

The other options do not use the correct verb form for the given sentence. Option B, "is increasing," is in the present continuous tense, which does not convey the continuous nature of the increase from the past to the present. Option C, "had increased," is in the past perfect tense, which does not match the time frame of the sentence (since 1900). Option D, "is going to increase," is in the future tense, which does not fit the context of the sentence describing an increase that has already occurred. Option E, "ha's been increasing," contains an error with the contraction "ha's" instead of "has" and also uses the present perfect continuous tense, which is not the appropriate tense for this sentence.

Therefore, the correct answer is "A. has increased."