From the passage, we can understand that El NiƱo is an event that has affected the global surface temperatures only in 2019 and that it is likely to persist through the rest of the year. So it is unlikely that it will have any long term effects. There is no comparison of moderate and weak El NiƱo in the passage. There is no mention about El NiƱo occurrence in 2016 and 2017, therefore, it would be incorrect to assume anything. From the data given it is clear that in 2019 the temperature, though high, is less than that of 2016 and 2017 so it is not true that global surface temperatures are increasing at a constant rate for the last three years. Hence the correct option is D.