A group of California scientists Wednesday urged state lawmakers to adopt a steeper target for cutting greenhouse gas emissions after 2020.

"California's leadership is needed now more than ever to address the risks of a dangerously warming climate," the Union of Concerned Scientists said in a letter signed by more than 100 scientists, researchers and economists and sent to Gov. Jerry Brown and state legislators.

The state is on track to meet its obligation to cut carbon dioxide and other heat-trapping gases to 1990 levels by 2020, according to the California Air Resources Board. But in a report last week, the agency recommended setting an interim target to ensure the state is on a path to reach its loftier goal of slashing emissions to 80% below 1990 levels by 2050.

"To achieve the steep reductions necessary to limit the worst impacts of climate change, lawmakers and regulators should adopt and implement enforceable emissions caps for 2030 and beyond," the letter from the science advocacy group said. It did not recommend a specific limit, but warned that "the longer we wait the harder and more costly it will be."

Also on Wednesday, state Sen. Fran Pavley (D-Agoura Hills) and state Sen. Ricardo Lara (D-Bell Gardens) introduced a bill that would require California regulators to prepare a post-2020 timetable for cutting emissions of carbon dioxide and other planet-warming pollutants like black carbon and methane.

State air quality officials said they already have the authority to require additional emissions cuts after 2020 but welcomed suggestions on exactly what the target should be.

"We think that there are a bunch of people who should weigh in, and this is probably the start of that process," said Dave Clegern, a spokesman for the Air Resources Board.

California's 2020 and 2050 greenhouse gas targets were set by executive order in 2005. The state's 2006 global warming law, called AB32, cemented the 2020 limit and set in motion many of California's climate change policies, including its low-carbon fuel standard and cap-and-trade program for refineries, power plants and other big emitters of carbon dioxide.

The Union of Concerned Scientists' letter said that putting a price on carbon dioxide through cap-and-trade "is key, but not sufficient to adequately reduce emissions." Achieving more dramatic cuts in greenhouse gases, the group said, will require new policies to promote renewable energy and a cleaner transportation system.

tony.barboza@latimes.com