California Gov. Jerry Brown on Wednesday accelerated the state's response to climate change by issuing an executive order calling for a reduction in greenhouse gas (GHG) emissions of 40% below 1990 levels by 2030.

Brown said the move was aimed at aligning California with "leading international governments" in advance of the United Nations climate talks in Paris in December and in keeping with a European Union emissions reduction target set for 2030.

The executive order also comes at a time when California's legislature is considering setting various climate-related goals for 2030, calling for up to a 50% cut in petroleum use, doubling efficiency standards for buildings, and raising the renewable portfolio standard to 50%.

Even before Brown's action, the Western States Petroleum Association (WSPA) was lobbying against a state legislative proposal (SB 350) calling for a 50% reduction in gasoline and diesel fuel use by 2030, given the absence of "available and affordable" alternatives.

While supporting the state's aggressive climate change push, WSPA President Catherine Reheis-Boyd said the climate goals would become "enforceable mandates" under SB 350, empowering the California Air Resources Board (CARB) with far-reaching authority. "We strongly encourage the legislature to not concede authority and decision-making to CARB," Reheis-Boyd said.

WSPA cites various sources and statistics on the impracticality of cutting petroleum use in half, noting that the U.S. Energy Information Administration forecasts that even with advances in various bio and alternative fuels, 80% of the U.S. energy portfolio will be made up of fossil fuels by 2040. California, the world's third-largest fuel consumer, has 34 million registered vehicles on the road and 96% of its transportation fuels are petroleum-based.

Brown acknowledged that the executive order "sets a high bar" for the state, other states and the nation as a whole, "but it is one that must be reached for this generation and generations to come." As with the state's proposed climate legislation, Brown's order gives CARB broad powers.

California officials said the state is on track to meet a target of 1990 GHG emission levels by 2020, and it has an existing executive order from former Gov. Arnold Schwarzenegger to reach a reduction of 80% below 1990 levels by 2050.