On Monday, California Governor Jerry Brown signed a bill mandating that the state's utilities move to 100-percent zero-emission electricity generation by 2045. Brown also issued an executive order today requiring the state to become carbon neutral by 2045, that is, mandating that the state remove as much greenhouse gas from the atmosphere as it puts into the atmosphere.

California is the most populous state to agree to such aggressive decarbonization and only the second state to formalize such a pledge in legislation, after Hawaii. Although California has phased coal plants out of its state-wide energy mix, it still relies predominantly on natural gas for the bulk of its electricity.

The bill was passed by California's Assembly and Senate in August. The votes weren't a sure thing: some Republicans and Democrats worried that such an ambitious goal would lead to increased energy cost for their constituents.

The state will have to lean more heavily on wind, solar, geothermal, and hydroelectric power to reach its goal, as well as seek more ambitious battery build-outs and create incentives for dramatic changes in energy efficiency at the industrial, commercial, and residential levels. Nuclear energy is probably not in the cards for the state in the near future: California recently moved to close its last nuclear power plant among its aging fleet, although it recently passed a bill to replace the capacity of that power plant with renewable resources. California's most recent bill only states that electricity has to be zero-emissions, so theoretically the state might be able to adopt a full carbon-capture system on a natural gas plant, like the one from NET Power, which is currently being tested in Texas.

One of the most interesting aspects of the zero-emissions bill signed today is that it also specifies that California can't increase the carbon emissions of another state to get cheap electricity. It appears that buying electricity from a coal plant in Nevada is fine if that electricity had been supplied prior to the bill's passing, but seeking out new out-of-state natural gas-fired plants to buy from would not be allowed.

The bill's ambitiousness is compounded by the executive order that Gov. Brown signed today. The order requires California to become carbon neutral by 2045. "The achievement of carbon neutrality will require both significant reductions in carbon pollution and removal of carbon dioxide from the atmosphere, including sequestration in forests, soils, and other natural landscapes," Brown's executive order states (PDF).

Of course, executive orders are more flexible than legislation passed by two houses and signed by the governor, but Brown's order reflects urgency in the face of climate change after a summer of record wildfires. Still, the order does try to hedge against overly disruptive solutions to the economy, stating "All policies and programs undertaken to achieve carbon neutrality shall seek to improve air quality and support the health and economic resiliency of urban and rural communities, particularly low-income and disadvantaged communities."