From left, European Central Bank President Christine Lagarde, European Parliament President Sassoli, European Commission President Ursula von der Leyen, and European Council President Charles Michel pose for photographers as they mark the 10th anniversary of the entry into force of the Lisbon Treaty at the House of European History in Brussels, Sunday, Dec. 1, 2019. (AP Photo/Olivier Matthys)

BRUSSELS (AP) — A new team of leaders took office at the helm of the European Union on Sunday, pledging to put the fight against climate change at the top of their agenda and foster European unity despite the likely departure of Britain from the 28-nation bloc.

Germany’s Ursula von der Leyen officially replaced Jean-Claude Juncker as president of the EU’s powerful executive arm, which polices EU laws and negotiates trade on behalf of member countries. The former German defense minister becomes the first woman in the post.

Former Belgian premier Charles Michel succeeded Donald Tusk as president of the European Council, meaning he will chair summits of national leaders and drive their common agenda forward.

In the company of European Parliament President David Sassoli and new European Central Bank President Christine Lagarde, Von der Leyen and Michel marked the start of their five-year terms in Brussels with events marking the 10th anniversary of the Lisbon Treaty, the EU’s rule book.

“Today we can present a unified face to the rest of the world. With more weight and greater coherence in a rules-based world,” Michel said. “Today we do more than look back, we celebrate a new beginning, with great enthusiasm and hope.”

Sassoli urged the EU’s main institutions the new team to deliver on the hopes invested in them by the more than 500 million citizens who make up the world’s biggest trading bloc.

“We need to turn the promises of the past few months into results that improve people's lives,” he said. “From the fight against climate change to tackling the rise in the cost of living, Europeans want to see real action.”

At the commission’s headquarters, as workers were still moving in office furniture and equipment, von der Leyen outlined her schedule, seeming somewhat relieved to be at work after “a difficult and bumpy start” getting her policy commissioners approved by the European Parliament.

Setting the tone for what she describes as “geopolitical commission,” Von der Leyen held phone talks with the leaders of China, South Korea, Turkey, Indonesia and Australia, with more due later.

Showing that she is hitting the ground running on an issue of major European concern, von der Leyen heads Monday to Madrid for the international climate conference.

“The European Union wants to be the first climate neutral continent in 2050. Europe is leading in this topic and we know that we have to be ambitious for our planet,” she told reporters.

On Friday, von der Leyen makes her first foreign trip and has chosen Africa. In Addis Ababa, she will meet with Moussa Faki Mahamat, chairman of the African Union Commission, as well as the president and prime minister of Ethiopia.

The future of Britain’s place in the EU should become clearer after the Dec. 12 election there.

Prime Minister Boris Johnson hopes to secure a majority to can push through the Brexit divorce deal sealed with the EU in October. Under the terms of that deal, the U.K. would leave the EU on Jan. 31 but remain part of Europe’s single market and bound by EU rules, until the end of 2020.

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Thomas Adamson in Paris and David Rising in Berlin contributed to this report.

From left, European Central Bank President Christine Lagarde, European Parliament President Sassoli, European Commission President Ursula von der Leyen, and European Council President Charles Michel pose for photographers as they mark the 10th anniversary of the entry into force of the Lisbon Treaty at the House of European History in Brussels, Sunday, Dec. 1, 2019. (AP Photo/Olivier Matthys)
From left, European Council President Charles Michel, European Commission President Ursula von der Leyen, European Parliament President Sassoli and European Central Bank President Christine Lagarde arrive for an event at the House of European History in Brussels, Sunday, Dec. 1, 2019. European institution leaders on Sunday marked the 10th anniversary of the entry into force of the Lisbon Treaty(AP Photo/Olivier Matthys)
From left, European Parliament President Sassoli, European Central Bank President Christine Lagarde, European Council President Charles Michel and European Commission President Ursula von der Leyen walk through the park on their way to an event at the House of European History in Brussels, Sunday, Dec. 1, 2019. European institution leaders on Sunday marked the 10th anniversary of the entry into force of the Lisbon Treaty(AP Photo/Olivier Matthys)
From left, European Central Bank President Christine Lagarde, European Parliament President Sassoli, European Commission President Ursula von der Leyen, and European Council President Charles Michel pose for photographers as they mark the 10th anniversary of the entry into force of the Lisbon Treaty at the House of European History in Brussels, Sunday, Dec. 1, 2019. (AP Photo/Olivier Matthys)
European Council President Charles Michel, second left, greets European Commission President Ursula von der Leyen as they attend an event to mark the 10th anniversary of the entry into force of the Lisbon Treaty at the House of European History in Brussels, Sunday, Dec. 1, 2019. At right is European Parliament President Sassoli, and second right is European Central Bank President Christine Lagarde. (AP Photo/Olivier Matthys)
European Commission President Ursula von der Leyen speaks during an event to mark the 10th anniversary of the entry into force of the Lisbon Treaty at the House of European History in Brussels, Sunday, Dec. 1, 2019. (AP Photo/Olivier Matthys)
European Central Bank President Christine Lagarde, left, greets European Commission President Ursula von der Leyen as they mark the 10th anniversary of the entry into force of the Lisbon Treaty at the House of European History in Brussels, Sunday, Dec. 1, 2019. (AP Photo/Olivier Matthys)