Updated Jan. 17, 2020, with federal appeals court dismissing the national youth climate lawsuit.

The wave of legal challenges that is washing over the oil and gas industry, demanding accountability for climate change, started as a ripple after revelations that ExxonMobil had long recognized the threat fossil fuels pose to the world.

Over the past few years: Two states have launched fraud investigations into Exxon over climate change and sued (one went to trial in 2019, and the attorney general lost). Nine cities and counties, from New York to San Francisco, have sued major fossil fuel companies, seeking compensation for climate change damages. And determined children have filed lawsuits against the federal government and various state governments, claiming the governments have an obligation to safeguard the environment.

The litigation, reinforced by science, has the potential to reshape the way the world thinks about energy production and the consequences of global warming. It advocates a shift from fossil fuels to sustainable energy and draws attention to the vulnerability of coastal communities and infrastructure to extreme weather and sea level rise.

From a trove of internal Exxon documents, a narrative emerged in 2015 that put a spotlight on the conduct of the fossil fuel industry. An investigative series of stories by InsideClimate News, and later the Los Angeles Times, disclosed that the oil company understood the science of global warming, predicted its catastrophic consequences, and then spent millions to promote misinformation.

That evidence ignited a legal clamor that included calls for a federal criminal investigation of Exxon. The challenges gained momentum when attorneys general in New York and Massachusetts subpoenaed the oil giant for internal climate change-related documents. Then some of the country's largest cities entered the fray, seeking billions of dollars to fortify against climate change.

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The storm of litigation could have a broad impact if it succeeds in holding fossil fuel companies accountable for the kinds of damages they foresaw decades ago, said Harold Koh, a professor of international law at Yale Law School who served as senior legal adviser to former Secretary of State Hillary Clinton.

"The industry has profited from the manufacture of fossil fuels but has not had to absorb the economic costs of the consequences," Koh said. "The industry had the science 30 years ago and knew what was going to happen but made no warning so that preemptive steps could have been taken."

"The taxpayers have been bearing the cost for what they should have been warned of 30 years ago," Koh added. "The companies are now being called to account for their conduct and the damages from that conduct."

Following is a summary of the major legal battles pitting Exxon and the oil and gas industry against American states and cities, and environmentally inspired young people against the government.

This timeline will be updated as events unfold.

Rex Tillerson, Exxon's former CEO and former secretary of state in the Trump administration, leaves court on Oct. 30, 2019, after testifying in Exxon's New York trial. Credit: Drew Angerer/Getty Images

State Attorneys General Investigate Exxon

The attorneys general of New York, Massachusetts and the U.S. Virgin Islands launched investigations of Exxon in 2015 and 2016. Prosecutors wanted to see if the company lied to the public about the risks of climate change or to investors about how such risks might hurt the oil business.

The investigations drew a quick, fierce response from Exxon. The company went on the legal offensive to try to shut down the probes, employing an army of aggressive, high-priced lawyers and a strategy of massive resistance. The attorney general of the Virgin Islands capitulated and ended his investigation just three months after issuing subpoenas.

In the years that followed, Exxon waged a relentless fight though state and federal courts to impede the state investigations. It sued Massachusetts Attorney General Maura Healey and then-Attorney General of New York Eric Schneiderman in federal court to block the investigations, but the judge rejected Exxon's claims that the investigations are politically motivated. Legal battles also spilled into the courts of both states; all the way up to the supreme courts of New York and Massachusetts.

In October 2018, then-New York Attorney General Barbara Underwood sued Exxon, stating in the lawsuit that the oil giant engaged in "a longstanding fraudulent scheme" to deceive investors by providing false and misleading assurances that it was effectively managing the economic risks posed by policies and regulations it anticipated being adopted to address climate change. The lawsuit said the alleged fraud reached the highest levels of Exxon, including former Chairman and CEO Rex Tillerson, who it said had known about the misrepresentations for years.

In October 2019, that lawsuit went to court before a justice in New York.

The same month, Healey, the Massachusetts attorney general, sued Exxon, alleging violations of the state's Consumer Protection Act and accusing the company of defrauding investors and threatening the world economy.

The New York judge issued his ruling in December, clearing Exxon of the investor fraud allegations. He wrote that the attorney general had failed to establish that any investor was misled, but added: "nothing in this opinion is intended to absolve Exxon from responsibility for contributing to climate change."

Key Events:

Nov. 4, 2015: New York Attorney General Eric Schneiderman issues first Exxon subpoena.

Feb. 29, 2016: Schneiderman announces formation of AGs United for Clean Power coalition.

April 4, 2016: Virgin Islands Attorney General Claude Walker issues subpoena to Exxon and the Competitive Enterprise Institute in a climate change investigation.

April 13, 2016: Exxon sues to block enforcement of Virgin Islands subpoena.

April 19, 2016: Massachusetts Attorney General Maura Healey serves Exxon with civil investigative demand (similar to a subpoena).

June 15, 2016: Exxon goes to federal court in Texas to block Healey's civil investigative demand.

June 16, 2016: Exxon goes to state court in Massachusetts to block Healey's civil investigative demand.

June 29, 2016: Virgin Islands withdraws Exxon subpoena and Exxon agrees to dismiss its related lawsuit.

Oct. 13, 2016: Texas federal judge orders Massachusetts' attorney general to submit to deposition by Exxon.

Oct. 17, 2016: Exxon seeks injunction in Texas federal court to block New York attorney general's investigation.

Nov. 7, 2016: Exxon challenges ruling that an accountant-client privilege in Texas law does not apply in New York and that its auditor, PricewaterhouseCooper, must turn over documents.

Nov. 17, 2016: Texas judge orders Massachusetts Attorney General Healey to appear in Texas for deposition.

Dec. 12, 2016: Judge issues order cancelling deposition of Healey.

Jan. 11, 2017: Massachusetts state court rules Exxon must comply with attorney general's civil investigative demand seeking climate change information.

March 29, 2017: Texas federal judge transfers Exxon's lawsuit to New York federal court.

May 19, 2017: Investigators disclose former Exxon CEO Rex Tillerson used a secret alias email under the name "Wayne Tracker."

June 2, 2017: New York's attorney general calls Exxon's climate accounting a "sham" under Tillerson.

Sept. 12, 2017: New York highest court denies Exxon's request to keep PricewaterhouseCoopers accounting records secret.

Jan. 12, 2018: Exxon seeks to amend its federal case against Healey and Schneiderman.

March 29, 2018: Federal judge rejects Exxon's attempt to derail the two state investigations. Exxon later appeals the ruling.

April 13, 2018: Massachusetts' highest court declines to block Healey's investigation into Exxon. Exxon later appeals the ruling to the U.S. Supreme Court.

Oct. 24, 2018: New York's attorney general files a formal complaint against Exxon.

Jan. 7, 2019: U.S. Supreme Court declines to consider Exxon's request to review the Massachusetts high court's decision.

Oct. 22, 2019: The Exxon case goes to trial in New York.

Oct. 25, 2019: Massachusetts' attorney general sues Exxon, alleging the company repeatedly violated the state's consumer and investor protection law and related regulations.

Nov. 8, 2019: Closing arguments are held in Exxon's New York trial. A ruling by the judge is expected as early as December.

Nov. 29, 2019: Exxon asks a federal court to assume jurisdiction—and dismiss—the Massachusetts consumer fraud lawsuit, saying the case hinges on federal not state law. Massachusetts prosecutors oppose Exxon's motion.

Dec. 10, 2019: New York judge clears Exxon of investor fraud allegations, but writes: "nothing in this opinion is intended to absolve Exxon from responsibility for contributing to climate change."

Along parts of the California coast, homes and cities are right at the ocean's edge and vulnerable to sea level rise and coastal erosion. Credit: Frank Schulenburg/CC-BY-SA-4.0

Cities Sue Over Climate Costs

Faced with the possibility of devastating consequences brought by rising sea levels, eight cities and counties in California, along with New York City and municipalities in Colorado and Washington state, have filed civil lawsuits against several oil and gas companies. Rhode Island became the first state to join them its own lawsuit seeking to fossil fuel companies accountable for the impacts of climate change.

The lawsuits make a public nuisance claim and, in some cases, allege negligence. Essentially the lawsuits say the oil and gas companies have known for decades that burning fossil fuels is one of the biggest contributors to global warming. Instead of acting to reduce harm, the cities charge, companies attempted to undermine climate science and mislead the public by downplaying the risk posed by fossil fuels.

In California, where the lawsuits seek billions of dollars to pay for mitigation measures, such as sea walls to protect coastal property, the oil and gas companies responded by seeking to move the cases to federal courts, where nuisance claims are less likely to succeed. That jurisdictional battle rages on. Two California cases that were moved to federal court were dismissed by a judge who said the dangers of climate change are "very real" but that the issue should be handled by Congress.

Key Events:

July 17, 2017: San Mateo County, Marin County and Imperial Beach file separate lawsuits in California Superior Court seeking damages from 37 fossil fuel companies over sea level rise.

Sept. 19, 2017: San Francisco and Oakland file lawsuits in California Superior Court seeking damages from five fossil fuel companies over sea level rise.

Dec. 20, 2017: Santa Cruz and Santa Cruz County file lawsuits in California Superior Court against 29 fossil fuel companies, seeking compensation for climate change-related damage.

Jan. 8, 2018: Exxon asks a Texas court to grant a discovery order allowing the company to question officials in counties and cities suing.

Jan. 9, 2018: New York City files suit in federal court against five fossil fuel companies over climate change-related costs.

Jan. 22, 2018: City of Richmond files lawsuit in California Superior Court against 29 fossil fuel companies.

March 16, 2018: Federal judge rules some of the cases should be tried in state court, creating a conflict with another judge who ruled similar cases belong in federal court.

March 21, 2018: Federal judge overseeing the San Francisco and Oakland cases hosts a climate change tutorial for the court. Chevron took the lead during the session. BP, Shell and ConocoPhillips filed statements agreeing with Chevron's comments; Exxon said its viewed differed.

April 17, 2018: In Colorado, the city of Boulder, Boulder County and San Miguel County file a lawsuit in District Court seeking to hold Exxon and Suncor accountable for costs related to climate change.

April 30, 2018: Five of the cities and counties file a response with the Securities and Exchange Commission after Exxon supporters called for the SEC to investigate them over their bond disclosures.

May 9, 2018: King County, Washington, files a lawsuit in King County Superior Court against BP, Chevron, ConocoPhilips, Exxon and Royal Dutch Shell over infrastruture, health and environment costs related to climate change. King County is home to Seattle.

June 11, 2018: In Colorado, Boulder and San Miguel counties and the City of Boulder add a claim of "civil conspiracy," alleging Exxon and Suncor Energy worked together to promote the use of fossil fuels while dismissing the consequences of climate change.

June 25, 2018: Federal judge dismisses the San Francisco and Oakland cases, saying the dangers of climate change are "very real" but that the issue should be solved by Congress. The cities later appeal.

July 2, 2018: The state of Rhode Island sues fossil fuel companies in state court over the effects of climate change.

July 19, 2018: A federal judge dismisses New York City's lawsuit, saying climate change should be dealt with by Congress and the president, not the courts. The city later appeals.

July 20, 2018: Baltimore sues 26 fossil fuel companies in state court in Maryland. A federal judge later rules the case should be heard in state court.

July 22, 2019: A federal judge rules Rhode Island's lawsuit should be heard in state court.

Young plaintiffs in the Children's Trust climate lawsuit head into court. Credit: Robyn Loznak

The Children's Climate Lawsuits

The next generation will likely have to manage the physical, ecological and economic fallout of climate change. And some of those young people are at the forefront of lawsuits that claim the federal government, and several state governments, are responsible for preventing and addressing the consequences of climate change.

The litigation, ignited by Our Children's Trust in 2015, relies on the public trust doctrine—a legal canon that stresses the government's hold on resources such as land, water or fisheries as treasure for the people. The children's lawsuits extend that principle by asserting the government also is a trustee of the atmosphere.

Nine similar children's lawsuits supported by Our Children's Trust have been filed in state courts from Alaska to Florida. Judges in Alaska, Oregon and Washington state dismissed three of the state-level cases; the youth in all three cases have appealed.

The federal case demands sweeping changes in federal climate efforts and in government programs that subsidize or foster development of fossil fuels. Both the Obama and Trump administrations, and the fossil fuel industry, repeatedly sought to have the case dismissed. The case had been scheduled for trial in federal court starting Oct. 29, 2018, but it was put on hold after the federal government appealed.

On Jan. 17, 2020, the U.S. Ninth Circuit Court of Appeals dimissed the case, saying the youth had no standing to sue and would have to appeal to the executive and legislative branches, not the courts.

Key Events:

Aug. 12, 2015: Our Children's Trust youth plaintiffs file lawsuit asserting the federal government is failing to protect them from climate change.

Nov. 12, 2015: American Petroleum Institute (API) and other pro-fossil fuel groups seek to intervene in Children's Trust case.

Nov. 17, 2015: Federal government requests dismissal of the case.

Jan. 14, 2016: Federal judge gives standing to API and other pro-fossil fuel groups to intervene in the case.

Nov. 10, 2016: Federal court in Oregon denies a government request to dismiss the lawsuit.

June 28, 2017: API and two other pro-fossil fuel groups are allowed to withdraw as interveners.

Nov. 16, 2017: Federal appeals court agrees to hear arguments on whether the case against the government can go to trial.

March 7, 2018: Federal appeals court rejects government's pleas to halt Children's Trust case.

April 12, 2018: Federal magistrate judge sets a new trial date: Oct. 29, 2018, in federal district court in Eugene, Oregon.

July 11, 2018: Nobel economist Joseph Stiglitz writes an expert court report supporting the children's case.

July 20, 2018: Federal appeals court again rejects a government request to halt the lawsuit.

July 30, 2018: U.S. Supreme Court rejects government request for emergency stay.

Oct. 15, 2018: Federal appeals judge releases President Trump as a defendant but rejects government requests to rule on the case without a trial.

Oct. 19, 2018: U.S. Supreme Court Chief Justice John Roberts issues a temporary stay following a Justice Department petition. The trial judge later delays the trial pending the court's decision.

Nov. 2, 2018: U.S. Supreme Court lifts its temporary stay, allowing the case to proceed.

Nov. 8, 2018: Federal appeals court issues a new temporary stay on the trial while considering a new petition from the government. On June 4, 2019, a court panel hears arguments on the petition.

Jan. 17, 2020: U.S. Ninth Circuit Court of Appeals dismisses the federal children's case.