During her time as San Francisco District Attorney, Harris created the Environmental Justice Unit in the San Francisco District Attorney's Office[230] and prosecuted several industries and individuals for pollution, most notably U-Haul, Alameda Publishing Corporation, and the Cosco Busan oil spill. She also advocated for strong enforcement of environmental protection laws.[231]
In October 2017, Harris was one of 19 senators to sign a letter to Administrator of the Environmental Protection Agency Scott Pruitt questioning Pruitt's decision to repeal the Clean Power Plan, asserting that the repeal's proposal used "mathematical sleights of hand to overstate the costs of industry compliance with the 2015 Rule and understate the benefits that will be lost if the 2017 repeal is finalized" and science denying and math fabricating would fail to "satisfy the requirements of the law, nor will it slow the increase in frequency and intensity of extreme weather events, the inexorable rise in sea levels, or the other dire effects of global warming that our planet is already experiencing."[232]
In September 2018, Harris was one of eight senators to sponsor the Climate Risk Disclosure Act, a bill described by co-sponsor Elizabeth Warren as using "market forces to speed up the transition from fossil fuels to cleaner energy—reducing the odds of an environmental and financial disaster without spending a dime of taxpayer money."[233] She stated that her goal would be achieving 100% of U.S. electricity from renewable energy sources, and that she supports a Green New Deal, an idea made popular by first-term Congresswoman Alexandria Ocasio-Cortez, because "climate change is an existential threat to all of us."[234]
In November 2018, Harris was one of 25 Democratic senators to co-sponsor a resolution specifying key findings of the Intergovernmental Panel On Climate Change report and National Climate Assessment. The resolution affirmed the senators' acceptance of the findings and their support for bold action toward addressing climate change.[235]
On July 29, 2019, Harris and Ocasio-Cortez introduced the Climate Equity Act, a bill that would lay out steps for Congress and the White House on how to go about guaranteeing policies that composed "a future Green New Deal protect the health and economic wellbeing of all Americans for generations to come." Referring to climate change as "an existential threat", Harris noted cutting emissions and ending American reliance on fossil fuels were not enough and cited the need "that communities already contending with unsafe drinking water, toxic air, and lack of economic opportunity are not left behind."[236]
In August 2019, Harris was one of fifteen senators to sign a letter to EPA Administrator Andrew Wheeler urging the EPA to ban chlorpyrifos given that the agency had found "that chlorpyrifos harms children's brains at exposures far lower than what the EPA allows" and warned that "more children, farmworkers and American families will be exposed to this pesticide and they will suffer as a result" of the EPA not reversing its decision.[237]
Harris and Egyptian President Abdel Fattah el-Sisi, holding a bilateral meeting at the COP28 climate summit in Dubai in December 2023.
On September 4, 2019, Harris unveiled a $10 trillion climate change plan intended to move the United States to a 100 percent renewable energy-based power grid by 2030 in addition to transitioning all vehicles in America to the same energy sources by 2035. She pledged to rejoin the Paris Agreement and end U.S. support for international oil and natural gas extraction projects, furthering that as president she would "hold polluters accountable for the damage they inflict upon our environment and set us on a path to a 100 percent clean economy that creates millions of good-paying jobs."[238]
In February 2020 Harris was one of seven senators to sign a letter to Secretary of the Interior David Bernhardt that called it "reckless and unwise" to remove protections to the Arctic after the U.S. Geological Survey found the Arctic to be warming faster than any other place on Earth and stating their support for "the strongest possible protections" for Special Areas within the National Petroleum Reserve-Alaska.[239]
In April 2020, in response to the proposed decision of the EPA to retain air quality standards from the Obama administration, Harris was one of 18 senators to sign a letter led by fellow Democratic senator Maggie Hassan asserting that the EPA "should be taking actions that will further protect health during this crisis, not put more Americans at risk."[240]
