BRUSSELS (Reuters) - Global temperature rises due to climate change could be kept below the critical 2 degree mark by fast international action to cut greenhouse gas emissions by 70 percent by 2030, a report said on Monday.

Scientists say that if temperatures increase beyond 2 degrees, humanity faces severe environmental fallout, such as melting polar ice caps and rising sealevels.

Increasing numbers of scientists and politicians question whether the 2 degrees goal is achievable, given the slow progress of international negotiations so far.

But it is not too late to avert dangerous climate change, said the report by consultancy McKinsey and backed by ten organizations including energy companies, Enel, Vattenfall and Royal Dutch Shell.

“Achieving the deep emissions cuts required to keep global warming below the 2 degrees limit is possible but difficult,” said McKinsey director Tomas Naucler.

Global investment of 530 billion euros ($686 billion) would be needed by 2020, and 810 billion by 2030, the report added.

Countries would offset much of the cost by simultaneously cutting their bills for oil, gas and coal, resulting in a net cost of less than 1 percent of gross domestic product.

The report comes one month after the European Union agreed ambitious measures to cut carbon dioxide and amid renewed optimism U.S. President Barack Obama will lend fresh momentum to global talks after having pledged to curb emissions at home.

Obama will start reversing former President George W. Bush’s climate policies on Monday with steps to raise fuel efficiency standards and to grant states authority to limit emissions from cars, officials say.

Keeping climate change manageable would require fast global action, said the report.

A 70 percent cut in emissions by 2030 would see greenhouse gas emissions peaking at 480 parts per million (ppm), roughly the level scientists say would cause a 2 degree rise.

But a 10-year delay would make it difficult to keep greenhouse gas emissions below 550 parts per million (ppm).

“Every year of delay adds to the challenge, not only because emissions will continue to grow during that year, but also because it will lock the economy into high-carbon infrastructure,” said the report.