The future of United States climate diplomacy has been cast further into doubt following President Donald Trump's decision on Tuesday to fire Secretary of State Rex Tillerson and appoint CIA Director Mike Pompeo in his place.

Pompeo is among the latest additions to a cabinet increasingly made up of staunch climate change deniers. He has previously expressed doubts over the scientific consensus on climate change and claimed that the landmark Paris Agreement forced the US to "bow down to radical environmentalists."

In contrast, his predecessor Tillerson had a comparatively moderate stance on climate issues, and even unsuccessfully tried to persuade Trump to keep "a seat at the table" at international climate talks.

Some have pointed out the irony in light of Rex Tillerson's former role as CEO of oil multinational ExxonMobil.

More quietly, Trump also appointed conservative television commentator and economic analyst Larry Kudlow as new director of the National Economic Council on Wednesday, in place of outgoing economic advisor Gary Cohn.

Like Pompeo, Kudlow is a climate change skeptic and overall has a questionable view on environmental issues.

In a notable 2013 segment on CNBC, Kudlow asserted his belief that the controversial Keystone XL Pipeline would be good for wildlife in the area because they would be able to "snuggle" under the pipeline to stay warm.

But how much damage could Pompeo really do as the most important diplomat for the US? The director of strategy and policy at the Union of Concerned Scientists, Alden Meyer, believes it comes down to his approach toward the role.

"Tillerson took a more hands-off approach," Meyer told DW, "But Pompeo has a much more skeptical attitude regarding climate change than Tillerson. If he appoints sub-cabinet positions that have a high degree of oversight, and they change US policy, it could be quite damaging."

Environmental groups hit back

Given the long list of pressing issues facing the US State Department right now — ranging from North Korea to the Iran nuclear deal — it is unlikely that climate change will be one of Pompeo's top priorities.

However, a number of environmental groups have already voiced concern over the potential damage the new secretary of state could do on the diplomatic stage.

"[Pompeo's confirmation] would not just be a contradiction of our country's values, it would be dangerous to our national security and the health of our planet," Sierra Club Executive Director Michael Brun said in a statement.

"Every single other world leader accepts climate science and every single other nation wants to be a part of the Paris Agreement, yet Trump wants to give the stewardship of our international relations to an extremist."

Other organizations including Greenpeace criticized Pompeo's strong ties to the Koch brothers, who were Pompeo's top funders during his time in Congress and who have consistently lobbied for environmental regulation rollbacks in the US.

"Mike Pompeo is uniquely unqualified to be Secretary of State in an entirely different way than Rex Tillerson was," Greenpeace USA Climate Director Naomi Ages said in a statement, "In addition to being a climate denier, like his predecessor, Pompeo is a Koch brothers' shill and a dangerous choice who will continue to denigrate the United States' reputation abroad and make us vulnerable to threats at home."

A tale of two cities

But despite Trump's attempts to disengage the US from the issue of climate change, many federal agencies, State Department envoys and government scientists remain active in international efforts to tackle the issue.

Read more: COP23: Rival US delegation opens pavillion to challenge Trump

Meyer says this reflects the current political reality within the US. "It's a tale of two cities, so to speak," he told DW. "People are looking ahead to the years after Trump."

"The US federal government has a slightly diminished role [regarding climate action], but the US as a country is a much different picture, where mayors and governors and activists and researchers are committed to carrying out decarbonization — in spite of Trump's efforts."

Who will fill the climate leadership void?

For a time, German Chancellor Angela Merkel was known as the "climate chancellor" due to her long-standing international engagement in climate diplomacy.

However, with Germany unlikely to meet the goals it set for itself, Merkel's image as a role model when it comes to climate action has diminished, particularly in light of the country's reluctance to phase out coal-fired power.

Following the withdrawal of the US from the Paris Agreement, few countries have attempted to fill the climate leadership vacuum.

French President Emmanuel Macron is arguably the most vocal on the issue — within hours of Trump's decision to pull out of the Paris climate agreement, he launched the tongue-in-cheek social media campaign, to "make our planet great again," and pledged €30 million ($37 million) to climate research.

Meanwhile, China is emerging as a somewhat unlikely leader on environmental issues as the influence of the US gradually recedes.

A recent government shake up saw China strengthen the role of its environment ministry in a bid to tackle major polluters and better manage the world's largest national carbon trading program.

But given that it still burns more coal than any other country, it remains to be seen how effective a climate leader China will be.