As international climate negotiators meet in Bonn this week to draft rules for carrying out the Paris Agreement on climate change, the United States delegation presents a wraithlike enigma.

Even though the Trump administration has renounced the treaty, the United States has not yet withdrawn, and Washington would like to influence the discussions. But the Trump foreign policy team, now more than ever, is a tight cabal of hard-line foes of climate action.

That puts the career diplomats who lead the U.S. delegation in an awkward spot as the rest of the world works out the details of the emerging Paris rulebook, due to be adopted by the end of the year. The American negotiators might like for it to provide for greater transparency and to avoid different rules for developed and developing nations, two long-standing goals of U.S. climate diplomacy. But they have no bargaining chips, such as money for sustainable development or bold targets for deeper cuts in U.S. emissions.

It has been jarring that the United States, historically the largest contributor to the world's carbon dioxide buildup and until recently a driving force behind the Paris Agreement, to be at the table but not ante up. Now, other players worry that President Donald Trump's new team will overturn the card table.

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That's particularly troubling at a time when Europe, China and other nations will in the next few years need to set more ambitious targets than they have committed to so far in order to meet the Paris goals of bringing net emissions of greenhouse gases to zero in the next several decades.

"People are trying to figure out how do you keep progress in the system without the U.S. as an active and positive contributor," said Alden Meyer, the director of strategy and policy for the Union of Concerned Scientists who has been attending these meetings for decades. "If that switches, and the U.S. becomes an active opponent or blocker, then you've got a bigger problem."

"That is the concern, given some of the statements [the new Trump administration appointees have] made about reality of the climate problem ... and their overall attitude to the Paris Agreement," Meyer said.

Denial in the White House

Trump's top advisers—none of whom are at the Bonn talks—now include Secretary of State Mike Pompeo, who has said that America should not "bow down to radical environmentalists"; chief economic adviser Larry Kudlow, who praised Trump's retreat from Paris as ending "the war on fossil fuels"; and national security adviser John Bolton, who views the accord as a threat to U.S. sovereignty. Trump's entire cabinet is overwhelmingly hostile to the climate treaty, but these three newcomers hold special sway.

Until recently, hope ran high among other delegations that Trump's previous top economic and foreign advisers would persuade the president to keep the U.S. commitment to Paris.

Former Secretary of State Rex Tillerson, well-acquainted with the history of climate negotiations as former chief executive of Exxon, had told Congress he believed that the U.S. should keep "a seat at the table." Former economic adviser Gary Cohn had given a warm hearing to former Secretary of State James Baker and allies who came to the White House early on to make the conservative case for a carbon tax—earning him the derogatory nickname "Carbon Tax Cohn" among his opponents on Trump's staff. And although Brig. Gen. H.R. McMaster, the previous national security adviser, muted his views on the Paris Agreement, many close observers, including President Obama's climate envoy Todd Stern, said they had expected him to be an advocate for the U.S. to stay in the agreement, a high priority for military allies in NATO and for possible adversaries like China.

But their advocacy ran headlong into Trump's zeal to fulfill his campaign promise to "cancel" the Paris accord. And they are all gone.

Fine Print and Lots of Dialogue

Trigg Talley, director of the U.S. State Department's Office of Global Change, is leading the team of career civil servants who are going through the paces during the talks this week in Bonn.

It's a mix of nitty-gritty deliberations on treaty technicalities and touchy-feely dialogue on broader issues of fairness and ambition, and nothing is expected to be resolved there. The aim is to reach consensus on the next steps in time for the annual Conference of Parties to the UN Framework Convention on Climate Change, COP 24, in the historic coal mining town of Katowice, Poland, at the end of this year.

The process "to bring the Paris Agreement fully to life and make it work in very real terms [is] the most critical moment for global political leadership on climate change since the outcome in Paris in 2015," said David Waskow, director of international climate action for the World Resources Institute.

The United States and China are co-chairing a working group on transparency issues—the rules to provide accurate and precise measurement, reporting and verification on the steps nations have taken to cut carbon emissions.

In addition to pushing for transparency, U.S. negotiators are expected to resist any efforts at "bifurcation," or separate pathways for rich and poor nations.

Both are stances that the U.S. has maintained in the talks through Republican and Democratic administrations alike.

Other gnarly questions include how much financial assistance to give poorer nations for controlling their pollution and adapting to the changing climate; how to compensate them for damages already being incurred, such as drought, famine, floods, storms and rising seas; and how to design workable international offsets so that nations can trade credit for pollution reductions among themselves in a yet-to-be-defined carbon marketplace.

"At this stage, at least, the politics around the State Department hasn't unduly affected [the U.S. negotiating team's] ability to carry forward with what I guess you could call the traditional U.S. negotiating objectives," Waskow said. "But the overlay for all of this is Trump's intention to withdraw from Paris, and I don't think we should be dissuaded at all from seeing that as the central orientation of the president and ultimately the administration."

The absence of U.S. leadership at Bonn may be keenly felt in the one-day session scheduled for May 8 dedicated to the so-called Talanoa Dialogue, the process to reexamine the commitments that individual nations have made so far. (Fiji, the current chair of the talks, chose the traditional word "Talanoa" to reflect a process of inclusive, participatory and transparent dialogue.)

So far, there are 48 submissions to the dialogue representing the views of 178 countries that are parties to the Paris Agreement, as well as hundreds of submissions by non-governmental organizations, addressing how nations might raise their ambitions. The United States is among about 20 nations that had offered no submission as of Wednesday. (Other large carbon emitters that have not made Talanoa Dialogue submissions include Canada and Brazil.)

The Intergovernmental Panel on Climate Change (IPCC) is scheduled to contribute to the discussion this fall in the form of a special report on the science behind a tougher goal, keeping global warming to 1.5°C above pre-industrial levels. But the national commitments that have been made under the Paris Agreement so far only get the world a third of the way to the goal of keeping the temperature increase below 2°C, as the United Nations Environment Program's "Emissions Gap" report showed last year.

"We don't have to wait for the IPCC report to know that we are way behind the curve," said Meyer.

Room for Hope?

Although few observers of the climate talks have illusions that the Trump administration—especially with its new foreign policy team—will offer to set stronger goals to cut carbon emissions, French President Emmanuel Macron's remarks before Congress last week demonstrated that some world leaders still hold out hope that the United States will return to the climate fight in the long run.

"I am sure, one day, the United States will come back and join the Paris Agreement," Macron told Congress. "Let us face it: There is no Planet B."

And when Pompeo, during his confirmation hearing, faced a question on climate change from Sen. Jeff Merkley, (D-Ore.), he replied: "I ... believe the climate is changing, that there's a warming taking place. I'm happy to concede that there's a human component to that. I'm equally prepared to tell you that as we find tools that are effective to prevent the risk to the United States ... the State Department ought to appropriately be involved in them." (In fact, human causes are behind most or all of the observed warming in recent decades, and the risks go beyond what affects the United States. International diplomacy also is needed to address the fact that the U.S. and other developed countries are largely to blame for the warming seen so far, which presents worse risks to nations like small island states that have contributed little to atmospheric carbon emissions.)

One avowed optimist is the Trump White House's former international climate adviser, George David Banks, who had supported staying in the Paris Agreement. He maintains that the hard-line U.S. stand puts the nation in a stronger negotiating position when it comes to the talks now underway. That's because the rest of the world knows the Trump administration is willing to walk away, he argues.

"The Trump administration could not have negotiated the Paris Agreement—it took the Obama administration to do that," argues Banks. "But now that the international community has invested so much political capital in the agreement, the Trump administration has much more leverage than a Hillary Clinton administration would have had in finalizing these points. It's an interesting situation."

But on top of the changes in Trump's top echelon of foreign policy advisers, recent staff turnover at the White House adds to uncertainty around the future U.S. role in the climate talks.

Banks, who served as a climate negotiator in President George W. Bush's administration, resigned from his Trump administration post earlier this year when he could not obtain a security clearance. Trump's top domestic energy adviser, Michael Catanzaro, has also resigned to return to his former lobbying practice. Banks and Catanzaro, both of whom have years of experience working on energy issues, have been replaced by two young newcomers to the field. GOP political operative Wells Griffith, whose only previous experience in energy was a one-year stint in Trump's Energy Department, has been appointed to lead international climate and energy strategy for the White House, while Francis Brooke, a former aide to Vice President Mike Pence who moderated a panel on fossil fuels at last year's climate talks, will take Catanzaro's place as top domestic energy adviser.

Observers also are watching to see if the Trump administration follows through on a plan, first reported by Bloomberg, to nominate Paula Dobriansky, who was a lead climate negotiator under President George W. Bush, as undersecretary for political affairs at the State Department. Dobriansky's past statements indicate that she accepts the reality of manmade climate change, although she favors "collaboration, not coercion," and close partnerships with industry. (When Bush backed out of the Kyoto accord, she gave credit to the oil lobby.)

For the time being, Meyer sees the U.S. negotiating team as significantly hampered by its lack of high-level support and the power to deal. If his assessment is correct, even if the U.S. returns to the Paris Agreement in the future, it may be under rules that it was unable to influence.

"You basically have a loss of leadership," he said. "The [U.S.] team is doing the best they can on the technical rules, but obviously they don't have as much leverage on that issue when they are not playing on other issues. They are negotiating with one hand tied behind their back, and that creates a vacuum that others are trying to figure out how to fill."