You can call it a comeback: The ozone layer is slowly recovering, scientists say, with a significant increase in stratospheric ozone, which protects the planet from solar radiation.

A United Nations scientific panel found that between 2000 and 2013, ozone levels went up 4 percent in mid-northern latitudes at 30 miles up. In the 1980s, scientists issued a dire warning about CFCs, man-made chemicals found in aerosol cans and refrigerants that released chlorine and bromine into the air, destroying ozone. In 1987, countries agreed to a treaty that phased CFCs out. "It's a victory for diplomacy and for science and for the fact that we were able to work together," Mario Molina, a chemist who co-wrote a 1974 study forecasting ozone depletion, told The Associated Press.

"More than 98 percent of ozone-depleting substances agreed over time have actually been phased out," says Achim Steiner, executive director of the U.N. Environment Program. If that hadn't happen, "we would be seeing a very substantial global ozone depletion today."

It's not all good news, though. MIT atmospheric scientist Susan Solomon told AP the chemicals that replaced CFCs contribute to global warming and are expected to increase significantly by 2050. Catherine Garcia

Canadians elect a new Parliament in national elections Monday, and polls suggest that Prime Minister Justin Trudeau could become the first Canadian leader in 84 years to be ousted after one four-year term with a parliamentary majority. Trudeau's Liberal Party is neck-and-neck with the Conservative Party and its leader, Andrew Scheer, though it seems likely neither party will win an outright majority of Parliament's 338 seats.

If the election results in Canada's first coalition government since 1972, the likely combinations would be Trudeau being joined by the New Democratic Party (NDP) or the Conservatives pairing up with the separatist Bloc Quebecois. NDP leader Jagmeet Singh has suggested he is open to a governing coalition with the Liberals, though Trudeau has not made similar public overtures.

The campaign has been "nasty," especially by Canadian standards, says CNN's Paula Newton. Trudeau's once-high popularity has been eroded by unmet expectations and a series of controversies and scandals, most recently his admission he has worn blackface on multiple occasions. The blackface controversy doesn't seem to have shifted public opinion much, and Scheer, a career politician who only recently disclosed that he holds dual U.S.-Canadian citizenship, has been unable to gain traction with his attacks on Trudeau.

The net result of the dirt-slinging has been a disenchanted electorate and "a desert from a public policy point of view," veteran Canadian pollster Nik Nanos tells CNN. "If people were to describe the election, it would be 'Indecision 2019.'" Preliminary results for Canada's 338 ridings, or parliamentary districts, are expected to be announced Monday night. Peter Weber

The Justice Department revealed in a court filing Sunday that former Special Counsel Robert Mueller did not make either Donald Trump Jr. or former White House Counsel Don McGahn testify before a grand jury he used for his Russia investigation. The filing was in response to U.S. District Judge Beryl Howell's ruling Thursday that the Justice Department was withholding too much information from the House Judiciary Committee in its ongoing wrangling with Attorney General William Barr over Mueller's evidence.

Howell appeared perplexed by Mueller's decision. "The Special Counsel's reasons remain unknown," she wrote in her opinion. "The reason is not that the individuals were insignificant to the investigation. To the contrary, both of the non-testifying individuals named in paragraph four figured in key events examined in the Mueller Report."

McGahn's lawyer offered one explanation, telling Politico that because McGahn "voluntarily agreed to be interviewed" for about 30 hours at Mueller's office, "there was no need for a grand jury subpoena." Former federal prosecutor Renato Mariotti found that explanation plausible. "If a witness agrees to be interviewed by FBI agents, as McGahn did, typically prosecutors won't put him in the grand jury to testify unless there's a concern that he will later change his story," he tweeted. "As for Trump Jr., this suggests to me that his lawyers said he would take the Fifth."

Lawyers for some of Mueller's other witnesses have said they believe Trump Jr. told Mueller's prosecutors he would assert his Fifth Amendment right against self-incrimination before the grand jury, and Mueller's team decided not to compel his testimony with a promise of immunity, Politico reports. Howell also noted in her ruling last week that Mueller declined to subpoena President Trump for an interview or grand jury testimony despite being dissatisfied with the president's written responses to his prosecutors' questions.

The upshot of Sunday's filing is that is strengthens the House Judiciary Committee's case "that Barr redacted the Mueller [Report] itself improperly," journalist Marcy Wheeler argues, because it hides the "non-testimony" of Trump and his son "behind frivolous redactions." Peter Weber

Acting White House Chief of Staff Mick Mulvaney went on Fox News Sunday in part to clean up a press conference Thursday in which he described President Trump's actions with Ukraine as a quid pro quo, trading military aid for an investigation of Democrats. Instead, Mulvaney created a new mess while trying to defend Trump's since-reversed decision to host next year's G7 summit at his own for-profit golf resort.

"At the end of the day, he still considers himself to be in the hospitality business," Mulvaney said of Trump, prompting Fox News anchor Chris Wallace to remind him: "He's the president of the United States."

"The bookended performances over the span of a few days were panned by the president's allies and cast doubt on Mulvaney's job security at the White House," The Associated Press reports. "Mulvaney's interview did not play well among Trump allies and advisers, with one calling it a 'self-immolation,'" Politico adds. Secretary of State Mike Pompeo declined to defend Mulvaney's Ukraine comments on Sunday, telling ABC News This Week, "I will leave to the chief of staff to explain what it is he said and what he intended."

On Fox News, Mulvaney said there is "absolutely, positively not" any consideration of his resignation, and a person close to Mulvaney told AP that Trump has expressed support for his acting chief of staff and Mulvaney is not aware of any effort to replace him. He may be right.

"Several White House aides and Trump allies presume Mulvaney's job is safe during the impeachment proceedings," partly because "no one else would want the chief of staff job right now and partly because Mulvaney is too much at the center of the Ukraine scandal for Trump to unceremoniously dump him," Politico reports. Mulvaney "was on thin ice, with diminished status in the White House," even before the Ukraine scandal hit, AP reports, citing nine staffers and outside advisers. And Mulvaney's job security isn't unique to him, AP adds. "The shortage of viable replacements has kept other officials in their posts months after [Trump] soured on them." Peter Weber

The Atlantic published a profile of Sen. Mitt Romney (R-Utah) on Sunday in which reporter McKay Coppins explained that "in the nine years I’ve been covering Romney, I’ve never seen him quite so liberated." At Slate, Ashley Feinberg appeared generally underwhelmed by Romney's apparent "effort to set himself up as the noble Republican foil to an out-of-control president," but she did find one interesting bit of news in the profile: "About midway through, the usually guarded senator revealed that, just like fellow lone-voice-of reason-haver James Comey, he was the owner of a secret Twitter account."

Romney told Coppins that he wasn't bothered by President Trump's Twitter attacks on him, explaining that he uses a secret Twitter account as "a lurker" to keep tabs on the political conversation. "I won't give you the name of it," Romney told Coppins, but he dropped enough clues — including that he follows Conan O'Brien but not Trump, because "he tweets so much," like his niece on Instagram: "I love her, but it's like, Ah, it's too much" — that Feinberg pretty quickly introduced the world to Pierre Delecto, @qaws9876.

Coppins called Romney after Slate published Feinberg's article. "C'est moi," Romney confirmed. Romney then took his secret account private, but Feinberg posted screenshots of some of Pierre's handful of tweets — usually, pro-Romney replies to other tweets — and intriguing catalog of likes, including several tweets from noted Trump critic George Conway and another tweet appearing to support invoking the 25th Amendment to remove Trump from office. There is one mystery Feinberg couldn't uncover, though: Pierre Delecto?

"'Pierre' certainly does seem like a name a Mitt Romney-type looking for an alias might choose, though the 'Delecto' is less clear," Feinberg wrote. Maybe it has something to do with his time as Mormon missionary in France. Read Coppins' profile of Romney at The Atlantic and Feinberg's unmaking of @qaws9876 at Slate. Peter Weber

Sen. Elizabeth Warren (D-Mass.) said Sunday that she will release a plan to pay for her Medicare-for-all goal "in the next few weeks." Democratic presidential rivals have been attacking Warren on her refusal to specify how she proposes to fund the plan, and reporters continue to ask her if she would raise taxes, not just lower total health care costs, for the middle class.

"The cheapest possible way to make sure that everyone gets health care is Medicare-for-all," Warren said at the end of a town hall in Indianola, Indiana. "Right now, the cost estimates on Medicare-for-all vary by trillions and trillions of dollars. And the different revenue streams for how to fund it — there are a lot of them," she added. "So this is something I've been working on for months and months and it's got just a little more work until it's finished."

Warren has mostly embraced the Medicare-for-all legislation introduced by fellow presidential candidate Sen. Bernie Sanders (I-Vt.), and the bill does not specify how it would be financed. The price tag for universal single-payer health care is usually put at about $30 trillion over 10 years, and supporters for such a plan argue that Americans and U.S. companies already bear that financial burden, at least, through health insurance and other medical costs.

Many of Warren's rivals favor a plan that would offer Medicare to any American who wants it. If every American wants it, they would, of course, have to find a way to pay for that. Peter Weber

South Bend, Indiana, Mayor Pete Buttigieg and Sen. Amy Klobuchar (D-Minn.) are still going after Sen. Elizabeth Warren (D-Mass.) in a continuation of the most recent Democratic presidential debate.

Both candidates appeared on CNN's State of the Union on Sunday, where they maintained their support for a public option in their health-care plans. Neither were satisfied with the Warren campaign's efforts to clarify how the senator plans to pay for Medicare-for-all, either. Both Buttigieg and Klobuchar reiterated they are wary of any plan that would kick people off their private insurance.

Klobuchar, for her part, also said her plan, which also includes a non-profit public option, would "build" rather than "trash" ObamaCare. Tim O'Donnell