INTERVIEW-Mankind can't afford more oil drilling-ex-BP exec

By Gerard Wynn

LONDON, Feb 13 (Reuters) - Known oil, gas and coal reserves may already contain a quarter more carbon than mankind can emit and still avoid dangerous climate change, putting the value of new oil exploration in doubt, said a former oil major executive.

The oil industry may be wasting $50 billion annually searching for new fields, said Jan-Peter Onstwedder, formerly BP's most senior risk manager. He left BP (BP.L) in December.

He calculated potential carbon emissions from proven oil, gas and coal reserves at around 700 billion tonnes, compared with about 500 billion tonnes which can be emitted this century and keep temperature increases within less dangerous bounds.

"It prompts the question where does more exploration fit, do we already have all the reserves we possibly need?" he said.

"I don't know whether they thought their strategy through."

Onstwedder spent six years as global head of risk covering supply and trade in oil, gas and other commodities, and which account for most of BP's sales and purchases.

He spent last year on sabbatical coordinating 10 investment banks in a "London Accord" climate change research project meant to pin-point cheapest cuts in carbon emissions, published in December.

Record high oil prices have made it economic to extract oil from formerly unattractive reserves such as oil-rich sands in Canada, and Onstwedder's calculations raise the question whether finding new such reserves makes sense.