"Nobody can predict what choices (the Trump) administration is going to make," Kerry told reporters Thursday. "I don't know, and I don't think you know."
"I think the question a lot of people ask is, 'Do they know?' " he continued. "And we're going to have to wait and see what choices they make."
But Kerry was emphatic in his support for President Barack Obama's foreign policy vision, and urged the country's future leadership to follow the same course.
He defended, in particular, the international agreement he helped negotiate to curb Iran's nuclear program.
That agreement, he insisted, "has made the world and our allies safer, including Israel and the Gulf states."
To terminate it would leave the US with the same "bad choices" of accepting a nuclear Iran o getting involved in another Mideast conflict as before the deal was struck, he said.
On addressing the "dire threat" of climate change, the secretary of state was equally emphatic, advocating for an agreement reached in Paris last year to cut global fossil fuel emissions.
"I think it's safe to say that in terms of environmental diplomacy, the past year may have been the most productive in history," said Kerry, a vocal proponent of measures to stem climate change.
"We do not believe we can shift into reverse or even stop in this endeavor," he said. "This is a race against time."
The secretary of state acknowledged some areas where the outgoing administration has fallen short in meeting its objectives, but nonetheless backed its approach.
Despite his tireless efforts to secure a peace agreement between the Israelis and Palestinians early in his tenure, the efforts ultimately floundered.
"The Israeli-Palestinian conflict continues," he said, "but we are absolutely right to support a two-state solution, and to warn about the danger of actions on any side that could obstruct that possibility."
In an exit memorandum released Thursday, Kerry said that although he worked hard to restart negotiations between the two sides, "unfortunately, the parties were not willing to make the difficult choices necessary to move forward with the negotiations."
In the memo, Kerry also highlighted progress toward degrading and destroying ISIS, as well as his own efforts to broker a ceasefire between Syrian President Bashar al-Assad and rebel forces to end their five-year war, "which has led to the worst humanitarian crisis since World War II."
"We're also right to insist that a diplomatic path is the only way out of the disastrous situation in Syria," Kerry told reporters. He said the US was pushing peace talks scheduled for later this month in Kazakhstan, expressing hope they could bring peace to the war-torn nation
Kerry rejected the notion that the United States' standing in the world has taken a hit over the past eight years.
"Overall," Kerry said, "I think when you consider the scale of the challenges that we faced, the speed with which we have had to act, the multiple, simultaneous crises that we faced, the limits imposed on our resources -- I think when you measure all of this, Americans can take enormous pride in what our diplomats and our leaders have been able to accomplish in order to advance the interests of our nation and keep our country safe."