Global warming threatens whales: reports

A record number of whales is expected to be spotted passing Sydney this winter, but scientists warn that global warming could put their future at risk.

The first big-picture review of the world's oceans shows human activity is driving changes at a rate not seen for millions of years. Many species are threatened and increases in disease are predicted.

This could have dire consequences for hundreds of millions of people, a series of scientific reports concludes. Oscar Schofield, of Rutgers University in the US, said environmental change had been profound in the West Antarctic Peninsula and was altering the food chain on which whales in that region depended.

Blooms of phytoplankton, or microscopic plants, had declined by 12 per cent in 30 years and the size of their cells had shrunk. This had allowed jellyfish-like creatures called salps, which find it easier to feed on the small cells, to start to replace shrimp-like krill, on which whales depend for food. Salps also eat the eggs and larvae of krill, which magnified the problem, said Professor Schofield, the co-author of one of the scientific reviews in a series, Our Changing Oceans, in the journal Science.

Ove Hoegh-Guldberg, of the University of Queensland, the co-author of another review, said the world's oceans were the heart and lungs of the planet, but they were showing signs of ill health due to greenhouse gas emissions.

"It's as if the Earth has been smoking two packs of cigarettes a day," he said. "We are entering a period in which the very ocean services upon which humanity depends are undergoing massive change and, in some cases, beginning to fail."

The oceans produce about 50 per cent of the oxygen we breathe but absorb 30 per cent of carbon dioxide emissions and more than 85 per cent of extra heat trapped as a result of global warming.

More acidic, warmer water, along with changes in circulation patterns, meant organisms such as corals, sea grasses, mangroves, salt marsh and oysters were starting to disappear, Professor Hoegh-Guldberg said. "Hundreds of thousands of species depend on these habitats."

Disease and invasive species were also becoming more common, such as the black-spined sea urchin, which has migrated south from NSW and is eating Tasmania's kelp forests.

NSW National Parks has launched a website, www.wildaboutwhales.com.au, with information about the giants as they journey north from Antarctica to mate and give birth in warmer waters.