With the clock ticking on his tenure, outgoing Secretary of State John Kerry vowed to continue speaking out on climate change issues, while touting what he regarded as one of the Obama administration's top accomplishments: the Paris climate change agreement.
The Paris Agreement sets out a global action plan to put the world on track to avoid dangerous climate change by limiting global warming to well below 2 degrees Celsius.
Kerry said 2016 "was the hottest in recorded history" in his remarks Monday to students and faculty of Massachusetts Institute of Technology.
WATCH: Hottest Years on Record
"All five of the hottest years on record have occurred within the lifespan of Twitter," Kerry added.
The reference to Twitter was seen as a response to President-elect Donald Trump, whose Cabinet selections signal a pointed policy shift on climate change.
Trump's decision to nominate ExxonMobil CEO Rex Tillerson as secretary of state means the department could be run by a lifelong oil executive. If Tillerson wins Senate confirmation, he would have a big say over whether the Trump administration withdraws from the Paris climate treaty.
According to Kerry, the United States and more than 120 other countries, representing more than 80 percent of the world's emissions, have joined the Paris Agreement.
On Monday, President Barack Obama launched a fresh defense of emissions curbs against Trump's plans to undermine the Paris climate deal.
Obama wrote in the journal Science that reducing greenhouse gases by adopting clean energy technology "can boost efficiency, productivity, and innovation."
WATCH: Kerry Discusses Fossil Fuels, Economy
Kerry said the adoption of the Paris Agreement sends a clear signal to the global marketplace, adding that for the first time, more of the world's money was invested in renewable technologies than in new fossil fuel plants.
"In the United States, more people are now employed by the renewable energy sector than by either the oil and gas industry or the coal industry," Kerry said.
He called climate change a "threat multiplier” because “the disruptions it creates can exacerbate challenges all over the world and because our own military readiness is adversely affected when our bases suffer the consequences of rising seas and stronger storms."
Last November, Kerry became the first sitting secretary of state to visit Antarctica.
"A scientist from New Zealand named Gavin Dunbar told me that what they're observing in Antarctica is 'the canary in the coal mine,’” Kerry said Monday, adding that "some thresholds, if we cross them, can't be reversed."
WATCH: Threat of Melting Glaciers