RNZ joins more than 250 media organisations from around the world in the Covering Climate Now (CCN) initiative by committing to heighten climate coverage in the week leading up to the UN Climate Action Summit on 23 September 2019.
The White House has stripped California of its right to set its own vehicle emissions standards and banned other states from setting similar rules.
The waiver allowed the state - America's most populous - to set stricter standards than the federal government.
President Trump says the move will cut car prices and the impact on emissions will be minimal.
But it is likely to spark a legal battle over states' rights.
California has already taken steps to block the administration's efforts.
"We will fight this latest attempt and defend our clean car standards," said Governor Gavin Newsom in a statement on Tuesday.
This is the latest clash between the Republican president and the state, a West Coast fortress of liberal Democrats.
What do the rules mean?
California's ability to set its own rules dates back to the 1970s when Los Angeles was blanketed in choking smog.
The state was allowed to set tougher emission standards than the federal government as long as it could provide a compelling reason for why the waiver was needed. In 1977, other states were allowed to adopt California's stricter standards.
The Golden State's rules have largely become the de-facto benchmark nationwide because car manufacturers do not design different sets of vehicles to meet different standards in different states. The state accounts for about 12 percent of all vehicle sales.
Emissions control methods first used in California, such as catalytic converters and regulations on oxides of nitrogen, have become commonplace throughout the US.
In July, under the waiver system, California conducted secret negotiations with Ford, Honda, Volkswagen and BMW of North America.
The car-makers pledged to produce fleets that meet a standard of 50 miles per US gallon (4.7 litres per 100km), against the current 37 mpg level, by 2026.
Increased fuel efficiency means vehicles burn less petrol and emit fewer greenhouse gases into the atmosphere.
Emissions from transportation, including cars and trucks, are the largest single source of greenhouse gases in the US, according to the US government.
Trump and the environment
Mr Trump's announcement is his latest move to roll back Obama-era environmental protections.
In June 2017, Mr Trump pulled the US out of the Paris Agreement, a climate pact forged under his predecessor involving nearly 200 countries.
In December of last year, under guidance from the White House, the Department of the Interior unveiled plans to allow oil drilling on millions of acres that have been off-limits to protect the greater sage grouse, a near-threatened species that spans 10 states in the US.
That same month, the Environmental Protection Agency (EPA) said it would end rules limiting carbon emissions on new coal plants, soon after the president dismissed a report by his own government warning of future devastating economic consequences to the US from climate change.
Also under Mr Trump, federal bodies have supported freezing emissions requirements for new cars and trucks at 2020 levels until 2026.
The administration has reportedly planned to issue separate rules to reverse Obama-era fuel economy requirements in the next few weeks.
What's the response?
Governor Newsom called the president's announcement "a failed attempt to assert power" and "a continuation of a political vendetta against CA and our progress".
Echoing the governor, California Attorney General Xavier Becerra vowed to head back to court. Mr Becerra has already sued the White House more than 50 times on a variety of issues including the proposed border wall, the reversal of the Affordable Care Act, and other environmental standards.
Among car manufacturers, Mr Trump's decision could prompt a split reaction.
Though automakers had previously lobbied the White House to relax standing environmental regulations, some manufacturers are reportedly worried that the legal challenges expected to result from the administration's intervention will add to existing market turmoil.
Moreover, some carmakers contend that without significant increases in fuel efficiency, US vehicles will be less competitive globally, ultimately resulting in job loss.
Among the public, support for stricter greenhouse gas emissions is strong. And according to a Washington Post-Kaiser Family Foundation poll released last week, 67 percent of Americans say they support state governments setting stricter fuel efficiency targets than the federal government.