In a significant policy shift, the Trump administration has overturned a crucial scientific determination made during the Obama era, which had underpinned federal efforts to mitigate the effects of planet-warming gases.

The 2009 "endangerment finding" had established that certain greenhouse gases posed a threat to public health, serving as the foundation for federal regulations aimed at reducing emissions, particularly in the automotive sector.

According to the White House, this reversal will result in cost savings of $2,400 per vehicle for automakers, making cars more affordable for consumers, and is being hailed as the "largest deregulation in American history".

Environmental organizations, however, view this move as the most substantial rollback of climate change measures to date and are preparing to challenge it in court.

During a statement in the Oval Office, President Trump described the 2009 ruling as a "disastrous" policy that had harmed the American automotive industry and driven up prices for consumers.

The President also criticized the Democrats' climate agenda, referring to it as the "Green New Scam", and characterized the 2009 ruling as a foundational element of this initiative.

The Environmental Protection Agency (EPA) initially addressed the impact of greenhouse gases in 2009, during the first year of President Barack Obama's presidency.

At that time, the agency determined that six key greenhouse gases, including carbon dioxide and methane, posed a danger to human health and the environment.

As Congress failed to pass legislation to address rising global temperatures, the EPA's finding became a cornerstone of federal efforts to regulate emissions in various sectors.

According to Meghan Greenfield, a former EPA and Department of Justice attorney, the "endangerment finding" has been instrumental in shaping US regulation of greenhouse gases, covering a wide range of industries.

Greenfield explained that the finding has had far-reaching implications, influencing standards for various sectors, including motor vehicles, power plants, and oil and gas production.

Administration officials argue that reversing the regulation will yield significant cost savings, exceeding $1 trillion, and will help reduce energy and transportation costs.

White House press secretary Karoline Leavitt stated that the reversal will save automobile manufacturers $2,400 per vehicle, which will ultimately benefit consumers.

Many environmentalists, however, are skeptical about the potential cost savings and argue that the move will have negative consequences.

Peter Zalzal from the Environmental Defense Fund warned that the reversal will lead to increased fuel costs, estimated at $1.4 trillion, and will result in more pollution from less efficient vehicles.

Zalzal also highlighted the potential health impacts, citing an estimated 58,000 additional premature deaths and 37 million more asthma attacks.

The rollback may create uncertainty for the US automotive industry, as manufacturing less fuel-efficient vehicles could limit their export potential.

Climate law expert Michael Gerrard noted that the reversal is, in effect, formalizing existing relaxations of fuel economy standards, but will ultimately harm the competitiveness of US automakers.

Gerrard warned that the move will make it challenging for US car manufacturers to sell their products abroad, as other countries may not be interested in purchasing less fuel-efficient vehicles.

While the reversal is intended to facilitate the rollback of climate change regulations, some observers anticipate unintended consequences.

During the process of overturning the finding, the Trump administration utilized the 2009 ruling to prevent states from implementing stricter carbon emissions laws.

The administration also employed the finding to dismiss "nuisance" lawsuits related to climate change, which were brought by individuals or organizations.

Meghan Greenfield noted that the "endangerment finding" has been effective in blocking numerous lawsuits and has limited the ability of plaintiffs to bring climate-related claims to court.

"I would expect states and non-profit groups to bring suits, probably primarily in our state courts, to try to figure out where the contours of this new law are."

A key aspect of the debate surrounding the reversal of the endangerment finding will center on the scientific basis for the decision.

The Department of Energy established a panel of scientists to produce a report challenging the widely accepted science on the impact of greenhouse gases, which was used to justify the initial proposal to reverse the 2009 finding.

However, many climate experts criticized the report, arguing that the panel was biased and that the findings were inaccurate and misleading.

Although it is unclear how heavily the Trump administration will rely on this report to defend their decision, a federal judge recently ruled that the Department of Energy had violated the law in forming the panel.

It is possible that the Trump administration is seeking a court challenge to the reversal of the endangerment finding, which could ultimately lead to a Supreme Court ruling.

Many legal experts believe that the administration aims to have the proposal tested in the Supreme Court before the end of Trump's term, hoping to secure a ruling that would permanently overturn the endangerment finding.

If the administration were to succeed in this effort, it would be difficult for a future presidential administration to reinstate the finding without new legislation.

According to Meghan Greenfield, the EPA's decision to exit the regulatory space entirely and seek a permanent reversal is a significant development.

"If they were to win that issue as they framed it before the Supreme Court, a new presidential administration could not change that position, in the absence of new legislation."