The US state has cut emissions to date partly by forcing companies to pay for their carbon pollution.
Governor Jerry Brown’s executive order is loftier than a federal goal that also aims to curb global warming, but it gives the state more time to achieve it.
Mr Brown’s plan lacks specifics, but he previously has cited increasing renewable electricity sources, reducing petroleum use in vehicles, doubling the energy efficiency of buildings and make heating fuels cleaner as ways to reduce emissions.
He set a target of reducing emissions to 40 per cent below 1990 levels over the next 15 years and called it the most aggressive benchmark enacted by a government in North America.
“With this order, California sets a very high bar for itself and other states and nations, but it’s one that must be reached – for this generation and generations to come,” Mr Brown said.
President Barack Obama announced a plan earlier this year to cut carbon dioxide emissions by 26 per cent to 28 per cent by 2025, with 2005 levels as the starting point.
California has already moved on its environmental goals, partly through a programme that puts a monetary value on carbon emissions.
In 2006, then-governor Arnold Schwarzenegger signed the state’s landmark global warming law, and Mr Brown has aggressively enforced it.
It called for reaching 1990 emissions levels by 2020 and 80 per cent below that by 2050. The state’s cap-and-trade programme, launched nearly three years ago, offers one of the few real-world laboratories on how to reduce carbon emissions.
It expanded this year to fine companies that produce gasoline and other fuels, prompting predictions that consumers will see a spike in prices to cover the costs.
Mr Brown said on Wednesday that climate change would factor into government planning, and he ordered state agencies and departments to implement measures to reduce emissions.
He also called for the state to identify how climate change will affect infrastructure and industry and what actions California can take to reduce the risks of climate change.
The order aligns California’s greenhouse-gas reduction targets with those of leading international governments ahead of the UN Climate Change Conference in Paris later this year.
The 28-nation European Union has set the same target for 2030.
Mr Brown’s action comes amid aggressive efforts aimed at fighting the state’s historic drought.