Based on long-term global temperature data, it is likely that overall temperatures were higher in 2015 than in 2008. This is part of a broader trend of rising global temperatures over the past century. So, the correct option is B.
The dataset from the maps describing land temperature anomalies for December 2008 and December 2015 indicates a trend in global temperature change. To accurately determine which statement best describes the data shown in the maps, one would need to compare the specific temperature anomalies reported for each of those months and years. However, based upon the referenced figures and data on global temperature trends, which show a long-term warming trend, it is likely that the maps would depict that overall temperatures were higher in 2015 than in 2008.
This is supported by the information indicating that the Earth's surface temperatures have increased over the past century and that there is a high confidence in an increase in the number of warm days and nights globally.
As for the specific regions like Europe or Africa, without the actual maps, we cannot conclusively answer parts C and D of the question. Nonetheless, given the broader trend of rising temperatures, it would similarly be likely, though not guaranteed, for Africa to experience higher temperatures in 2015 compared to 2008. However, region-specific anomalies can occur due to various factors affecting regional climates differently.