California Gov. Jerry Brown signed a bill into law Monday to move the state to be 100-percent dependent on renewable energy by 2045.

"It's not going to be easy and will not be immediate, but it must be done," the outspoken Democratic governor said in a statement. "California is committed to doing whatever is necessary to meet the existential threat of climate change."

The bill's target is nonbinding. The state's current renewable energy mandate, however, calls on the state's utilities to derive half of their electricity for the state from wind, solar, and other renewable source by 2030. The new bill would increase that target by 10 percentage points in the same time frame.

Brown signed the bill one day before he opens a weeklong global climate change summit in San Francisco. The summit is meant to show support for the Paris climate change deal, especially in the wake of President Trump's decision to exit from the accord last year.

Environmental groups are using the climate summit to rally against the Trump agenda to repeal regulations that made up former President Obama's climate change agenda.

The group 350.org, a anti-fossil fuel group committed to moving the globe to 100 percent renewable energy, called Brown's signature a historic moment for their campaign to move the country away from fossil fuels completely.

"To see California, the world’s 5th largest economy, commit to the 100% goal, is an historic moment and testament to the growing power of this movement," said May Boeve, 350.org's executive director.

Activist billionaire Tom Steyer announced Monday that he will be opening the summit in San Francisco on Tuesday by addressing a panel with 350.org co-founder Bill McKibben and former Environmental Protection Agency Administrator Gina McCarthy.

Steyer will be addressing the forum throughout the week, specifically focused on countering the Trump administration's agenda, according to his group NextGen America, which is sponsoring the California climate summit.

"As the Trump administration tries to drag the country backwards and undo progress on climate action made by individual states, political courage and solidarity are needed now more than ever," the group said in announcing Steyer's summit visit. "By sponsoring the Global Climate Action Summit, NextGen is building on its legacy of mobilizing for action on climate change and environmental justice."