How is climate change effecting the great barrier reef?

It increase temperature leading to coral bleaching.

Its a mix of multiple things! coral bleaching and human impact, the plans for development on the area and the higher tourist rates, theres also a mining plan in which will negatively impact it as the mine will be placed on the outskirts of the great barrier reef, therefore the emissions from the coal mine will waft up in to the ocean affecting the micro organisms and other life within.