ISTANBUL — Little was expected of this year's Group of 20 Leaders' Summit. It was a muted affair, presented virtually during a resurgent global pandemic. Its host, Saudi Arabia, was criticized by human rights groups for a record of abuses. And its most prominent participant was Donald Trump, an ardent opponent of the kind of collective global action the summit set out to achieve, who leaves office in less than two months.

Even so, as the two-day conference ended Sunday, its organizers hailed it as a success. A final communique heralded achievements, including an offer of debt relief to developing nations and a commitment to ensuring equitable access to coronavirus treatments. But it also laid out a frightening litany of challenges facing economies and societies that the scaled-back summit, or any global gathering, would be hard-pressed to meet.

“We underscore the urgent need to bring the spread of the virus under control,” the leaders of the G-20 nations said in the communique. And throughout the summit, dominated by the pandemic and its ravages, they argued that only collective action could bring the crisis to heel.

The plea for a coordinated response reflected the struggles faced by countries such as France, India and Turkey as infection rates soar. It was also a retort to the Trump administration and its go-it-alone approach to international challenges ranging from the pandemic to climate change.

“We have seen very clear signs but also actions by the G-20 supporting multilateralism,” Mohammed al-Jadaan, Saudi Arabia’s finance minister, said during a news conference at the summit’s conclusion. He mentioned the group’s support for institutions including the World Health Organization. The Trump administration gave a year’s notice of the U.S. withdrawal from the WHO in July; President-elect Joe Biden has said he would stop that process.

German Chancellor Angela Merkel said Saturday that “if we stand together worldwide, we can control and overcome the virus and its consequences.”

Trump confirmed his attendance at the summit the day before it began. In remarks to the group Saturday, he touted his administration’s record in combating the virus, saying it had “marshaled every resource.” He made no promise to expand the availability of U.S. vaccines. Then he played golf.

On Sunday, Trump addressed a summit session on the environment titled “Safeguarding the Planet.” The president, whose administration has weakened regulations intended to reduce pollution generated in the United States, called his record on protecting the environment “historic” and attacked the Paris climate accord.

On the day after the election this month, the United States became the first and only nation to withdraw from the 2015 agreement to curb greenhouse gas emissions.

“The Paris accord was not designed to save the environment,” Trump told the summit. “It was designed to kill the American economy.”

Biden, who has called climate change “the existential threat to humanity,” has pledged to rejoin the Paris accord.

In the weeks leading up to the summit, the kingdom faced protests from Saudi and international human rights groups demanding that world leaders downgrade their representation or boycott the gathering altogether. They argued that the summit conferred respectability on a government accused of grave abuses, including jailing and torturing female activists and killing Washington Post contributor Jamal Khashoggi at the Saudi Consulate in Istanbul in 2018.

No invited world leader boycotted. But neither did the remote gathering, which participants attended by video link, provide Saudi Arabia with the kind of platform it had sought to showcase its accomplishments.

The World Bank has said the pandemic could drive as many as 150 million people into extreme poverty, reversing decades of progress. UNICEF has warned that unequal access to technology among students in poorer countries threatens to “deepen the global learning crisis.”

Collaborative global efforts are needed to meet the “huge challenges” facing students and schools worldwide as they strain to adapt to distance learning, Hamad al-Sheikh, Saudi Arabia's education minister, said Sunday.

Saudi Arabia, with virtually unmatched financial resources, has been able to dedicate satellite channels to distance learning, he said. The kingdom has partnered with Microsoft to boost server space for online instruction. Education that “blended” in-person and distance learning would become the norm, even after the worst ravages of the pandemic had passed.

“No one expected that 1.6 billion students will be outside of schools,” Sheikh said. He acknowledged that few countries have comparable resources to respond to such a crisis.

“Some countries don’t have the capability to launch satellite stations,” he said.