By Environment Correspondent Alister Doyle

WARSAW (Reuters) - The United Nation's panel of climate experts revised estimates of historical greenhouse gas emissions, made in September, both up and down on Monday but said the errors did not affect conclusions that time was running out to limit global warming.

More heatwaves, floods and rising sea levels are forecast in the report from the Intergovernmental Panel on Climate Change's (IPCC), which guides governments on shifting towards cleaner energy sources.

The panel had hoped to avoid more corrections after an embarrassing error about Himalayan ice-melt in its 2007 report.

"I don't see it as a significant change," IPCC chairman, Rajendra Pachauri, told Reuters on the sidelines of a November 11-22 meeting of almost 200 nations in Warsaw, Poland.

Among changes, the IPCC revised down the cumulative amount of carbon emitted since 1860-1881 to 515 billion tons from 531 billion given in September, and revised up the amount emitted since 1750 to 555 billion tons from 545 billion.

Global emissions are now running at about 10 billion tons of carbon a year, meaning those change are equivalent to about a year to a year and a half of emissions.

"Errors in the summary for policymakers were discovered by the authors of the report after its approval and acceptance by the IPCC," it said in a statement.

It did not say how the errors had been made.

The IPCC says the world has emitted more than half the estimated 1 trillion ton of carbon viewed as the maximum to keep temperatures within safe limits at below two degrees Celsius (3.6 Fahrenheit) above the period 1861-1880 with more than a two-thirds probability, it said.

Many experts say that the world has only a few decades left before breaching the IPCC safety limits unless tough action is taken to cut emissions.

When asked if the correction would affect the credibility of the IPCC, Pachauri said, "I don't think so."

The IPCC's September report said the probability that most climate change since 1950 is manmade increased to 95 percent from 90 percent in 2007.

Bob Ward, of the London School of Economics, said Monday's correction made little difference to the overall carbon budget of a trillion ton.

"Climate change `skeptics' will no doubt desperately seize on these corrections and falsely allege that it undermines the whole report, but the public and policy-makers should not be fooled by such claims," he said in a statement.

(Editing by Louise Ireland and Nina Chestney)