Glen De’ath and Katherina Fabricius, two co-authors from the recent science paper on the decline in coral calcification on the Great Barrier Reef were interviewed by Australian ABC radio this afternoon. Listen online below, or read on after the jump for a transcript.

[audio:http://67.220.225.10/~clim2165/cs/audio/20090102-am07-coral-decline.mp3]

update: fixed the link to the correct interview.

ELEANOR HALL: The tipping point for catastrophic climate change is an issue of dispute between politicians and environmentalists.

But on the climate vulnerable Great Barrier Reef, researchers have been surprised to discover that a tipping point for coral growth has already been reached.

In the journal Science this morning they reveal that it was reached 18 years ago, as Nonee Walsh reports.

NONEE WALSH: At The Australian Institute of Marine Science in Townsville, researchers switched from studying coral death to examining its life. The giant Porites coral has density bands like a tree does and Dr Glenn De’ath says they looked at their growth story from 1572 onwards.

GLEN
DE’ATH: Prior to about 1990 coral growth was fairly consistent but round about 1990 things have change and we’re suggesting this is the tipping point. What’s happened basically coral calcification, that’s a measure of how corals grow, has decreased by about 14 per cent since then. Now we’re experiencing growth which is now consistently declining. We estimate roughly, if this rate continues, which is accelerating, then the coral growth will hit zero round about 2050.

NONEE
WALSH: A co-researcher Katharina Fabricius says 2050 matches calculations from the die off of coral reefs around the world, but the 1990 tipping point was a surprise.

KATHARINA FABRICIUS: We expected ongoing changes or more stressful conditions that change gradually over time but we’re finding a very strong tipping point. We don’t know the causes for the decline but there are some synergistic effects between increasing frequencies of stressful warm conditions and ocean acidification.

NONEE WALSH: Oceans absorb carbon dioxide from the air to create carbonic acid and Dr Dea’th says that’s an additional threat for coral which is affected by rising temperatures.

GLEN DE’ATH: We think it’s likely that the two of those are producing this dramatic change in the coral growth. One thing about the calcification decline we’ve noted is it consistently covers the whole of the Great Barrier Reef pretty much and if it was due to water quality for example, you’d expect it to be only affecting inshore reefs and that’s not the case. It seems to be consistent across the whole reef.

So it’s the fact that really temperature and acidification affect the whole reef, that’s one of the factors which make it more likely that they are the cause.

NONEE WALSH: The Porites coral is an important reef builder. It’s the toughest one and less vulnerable to environmental change than the other 400 corals of the Barrier Reef. Dr Fabricius says they seem to need what is probably now the unattainable CO2 levels of the recent past.

KATHARINA FABRICIUS: There are still amazing, beautiful reefs in the Great Barrier Reef, especially the far north. It’s just breath taking in some places. But there are larger and larger areas that look degraded and that will continue. I mean, projected for in 20 years’ time will mean be even lower coral cover, even slower coral growth, a great amount of erosion. And eventually the coral reefs will be very simple, dull looking ecosystems.

ELEANOR HALL: Dr Katharina Fabricius from the Australian Institute of Marine Science, speaking to Nonee Walsh.