The atolls have shown resilience to gradual sea-level rise, with atolls and reef islands being able to grow under current climate conditions by generating sufficient sand and coral debris that accumulates and gets dumped on the islands during cyclones. Gradual sea-level rise also allows for coral polyp activity to increase the reefs. However, if the increase in sea level occurs at faster rate as compared to coral growth, or if polyp activity is damaged by ocean acidification, then the resilience of the atolls and reef islands is less certain. The 2011 report of Pacific Climate Change Science Program of Australia concludes, in relation to Tuvalu, states the conclusions that over the course of the 21st century: