Marine heatwaves have caused the loss of over 100,000Ha of kelp forest in Australia in recent decades. In many parts of Australia, however, kelp forests are thriving. So how can we predict the vulnerability of kelp forests to climate impacts and what are the ecological implications of losing kelp forests for temperate reef function? Here I discuss how different models of climate change vulnerability compare to empirical changes in kelp forests across Australia over recent decades. I then explore how observed changes in kelp forest cover and composition have impacted the productivity and biodiversity of coastal ecosystems in Tasmania over the past 40 years. Our results highlight that while kelp forest loss has varied dramatically, kelp forests across Australia are vulnerable to marine heatwaves. Further, while warming has resulted in only minor changes in phenology and productivity at an individual level, changes in kelp forest composition over the past four decades has led to major declines in forest productivity. Our results highlight that kelp forests across Australia are particularly vulnerable more frequent marine heatwaves. The ecological implications of kelp forest loss have already been profound and requires urgent action to mitigate further collapse of kelp forests ecosystems in Australia.