Oil and gas company valuations are based, in part, on their reserves – volumes of oil or gas yet to be developed from assets in their possession. But the International Energy Agency has said that to avoid catastrophic climate change, a third of global fossil fuel reserves must be off-limits until 2050. And if governments take steps to heed the IEA’s  writes Quartz’s Todd Woody.

How will company valuations change if climate change imperatives demand that those reserves not be burned as fuel?

“Investors that control $3 trillion in global assets want to know what 45 multinational oil, coal and mining companies intend to do about $6 trillion in potentially ‘stranded assets‘.”

Some oil companies’ market values could be cut by half, according to HSBC. But some companies, such as BP, would be spared.

“25% of BP’s oil and gas reserves were at risk from being declared ‘unburnable.’ But those reserves only represent 6% of BP’s market value as they’re considered low-value.”