Washington, D.C. ? President Barack Obama is expected today to give California and other states the green light to impose their own, stricter fuel emissions standards.

Obama was scheduled to make a significant announcement on climate change midday at the White House, press aides said Sunday. Aides declined to confirm details.

An e-mail from the White House public liaison office to interested parties, including environmental activists, invited their representatives to attend an “important” ceremony to mark “the first environment and energy actions taken by the president helping our country move toward energy independence.”

Sierra Club spokesman David Willett said that in addition to instructing the Environmental Protection Agency to sign the waiver allowing the states to go forward, activists expected the president to make announcements of improving national fuel economy standards and creating green jobs.