In 1995, the temperature of the Red Sea rose abruptly. It's already-warm waters became 0.7°C hotter, which is a significant amount for a body of water whose reefs support life that's adapted for a very specific temperature. Scientists studying the Red Sea recently published a study using satellite data to prove that the temperature spike led to an overall increase in the sea's temperature over time.
According to the study's authors, writing in Geophysical Research Letters:
Using satellite-derived sea surface and ground based air temperatures, it is shown that the Red Sea is going through an intense warming initiated in the mid-90s, with evidence for an abrupt increase after 1994 (0.7°C difference). The air temperature is found to be a key parameter that influences the Red Sea marine temperature. The comparisons with Northern Hemisphere temperatures revealed that the observed warming is part of global climate change trends. The results also raise additional questions regarding other broader climatic impacts over the area.
It seems that the main cause of the Red Sea warming is hotter air in the region. There is no explanation yet for why 1995 was the tipping point.