A new piece in our Expert Voices section offers a pretty sobering look at the immense challenge of cutting carbon emissions while global energy demand keeps rising.

The big picture: Richard Newell and Daniel Raimi of Resources for the Future note impressive solar cost declines and the surge in renewable power, but caution that it's not yet time to declare that the transition from fossil fuels is underway.

• Instead, they note that so far the renewables gains have been a matter of "addition, not transition."
• "Although the percentage shares of biomass, coal and oil in our energy supply have fallen with the rise of alternatives, their total use continues to grow," they write. The chart above illustrates this.

Why it matters: A few points from their piece...

The world has never experienced an energy transition, but the challenge of climate change means that, for the first time, one will need to begin.

To avoid the worst impacts of climate change, renewables and new technologies will need to do more than build atop CO2–intensive fossil fuels — they will need to push out incumbents while at the same time expanding global energy access and reducing the system’s environmental footprint.

Read the whole piece in the Axios stream.

Quick take: Their article is among several recent reminders that massive tech advances and rising renewables deployment haven't, by themselves, put the world on a pathway to avoiding hugely dangerous levels of global warming.

• BP's chief economist made some similar points about the global energy mix with a separate chart during a recent presentation that I wrote about here, where he noted that coal's share in the global power mix has remained at 38% over the last 20 years.
• And don't forget, separate reports in recent months have concluded that global CO2 emissions actually rose in 2017, ending a three-year plateau.

Axios' Dan Primack has a good look at Tesla CEO Elon Musk's troubled rollout of his intention to take the electric automaker private.

Why it matters: Musk is in a perilous spot, in part over his market-moving tweet that he has "funding secured" for the huge transaction. As you may know already, Musk later said he was referring to discussions that he said revealed strong interest from a Saudi Arabian sovereign wealth fund.

Let's pick things up with Dan's reporting on the Securities and Exchange Commission's inquiry...

What's next: The SEC wants answers from Tesla. And from Musk, who argues his tweets were an attempt to be transparent with all Tesla shareholders, rather than only sharing his intentions with a small group of large investors.

• Former SEC enforcement attorney John Reed Stark believes that the SEC has a high hill to prove market manipulation, because such charges typically require the actor to both make ironclad false statements and attempt to profit from those statements.
• He adds that it's not technically a two-pronged test, so much as " indicators which shed light on the suspect’s actual intent."
• On the other hand, ex-SEC chair Laura Unger, said on Cheddar of Musk's initial tweet: "It was not true and accurate...[it] was quite a big overstatement, that he had financing secured, and one that was clearly misleading to the marketplace."

Threat level: The SEC doesn't really have a recent enforcement record on take-private transactions, but it would have wide latitude were it to find malfeasance. It could try to fine Musk and/or Tesla, while Musk also could be banned from serving as an executive or director of Tesla or any other public company.

Go deeper: Read Dan's full story on the Axios stream.

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President Trump's pick to run DOE's Advanced Research Projects Agency-Energy (ARPA-E) told lawmakers he supports the White House budget plan and is excited to run the program.

That shouldn't be noteworthy, except, well, the White House budget plan would kill ARPA-E, a popular project that supports R&D into next-wave clean energy tech.

What they're saying: An exchange between nominee Lane Genatowski and Sen. Angus King distilled this awkward dynamic. Here's part of their chat at a Senate energy committee hearing...

• King: Do you support the president’s budget or do you think ARPA-E has an important mission?
• Genatowski: I support the president’s budget, and I'm here because I’d like to get a chance to run ARPA-E and put my oar in the water and help it out to be as better as it can be.
• King: You understand the nature of the question...
• Genatowski: The dichotomy? I do.
• King: I'm seeing two guys sitting at the table here. You either support the president’s budget, which is zero, or you want to run an agency that has an important mission in this country that’s supported year after year by this Congress.
• Genatowski: I guess in my mind I can hold both concepts and they wouldn't be inconsistent. If the Congress votes to appropriate money...the president signs the bill, there will be a budget for ARPA-E, and I'd like to be the person that runs it.

The intrigue: The back-and-forth is part of the unusual role ARPA-E is now playing in the Trump era.

• The White House has repeatedly proposed ending the program, but it has strong support across the aisle (it's currently funded at $353 million), so Congress keeps saying no.
• Energy Secretary Rick Perry praises ARPA-E and doesn't even bother defending Trump's moves to end it.
• Genatowski told Sen. Joe Manchin that nobody even brought up ending ARPA-E during his vetting.

The bottom line: It's an example of how, in the shadow of White House hostility to climate initiatives, some of that work is still going forward.

Axios' Andrew Freedman sizes up the significance of Interior Secretary Ryan Zinke's appearance on the Fox Business Network, where on Thursday morning he broke sharply with scientific consensus regarding mankind's role in climate change.

Why it matters: Zinke oversees the agency that manages U.S. public lands, some of which are currently on fire due to hotter, drier weather that scientists say is part of long-term climate change.

• And Interior helps drives energy policy, thanks to its decisions about drilling, renewable power and mining on vast swaths of lands and coastal waters.
• How Zinke views climate science findings will help inform his approach to all of this.

The exchange: "Do you believe climate change is real and that man is the cause?" Fox Business host Neil Cavuto asked Zinke, who replied:

"It's clear in the forest fires that the temperatures are being elevated, the fire season's extended, it's longer, and there's no dispute about that. There's no dispute the climate is changing, although it has always changed. Whether man is the direct result, how much of that result is, that's still being disputed."

The big picture: Zinke's comments go against core findings of the climate science community. For example, a 2017 peer-reviewed report that included contributions from Interior scientists found that the period from 1901 to 2016 "is now the warmest in the history of modern civilization."

Read more of Andrew's story.

Batteries: Via The Financial Times, "US battery start-up Sila Nanotechnologies, which has a partnership with BMW, has raised $70m in funding from investors including Siemens’ venture firm Next47 and Japan’s ATL."

• The big picture: "The startup’s announcement adds to more than $1.5 billion that’s poured into the energy storage sector so far this year — roughly triple the total from the same period last year — as investors rush to lay bets on technologies that could deliver longer-lasting gadgets, cheaper electric vehicles, and cleaner power grids," MIT Technology Review reports.

Renewables: Per Greentech Media, "'Digital utility' startup Arcadia Power announced a $25 million fundraising round on Thursday and a 120-megawatt community solar pipeline through 2020."

Drilling: "A.P. Moller-Maersk said on Friday it would spin off its offshore drilling operation and list it in Copenhagen next year, the latest move by the Danish shipping company to focus entirely on transport and logistics," Reuters reports.

Musk, in his first interview since the tumult exploded around his plans to take Tesla private, tells the New York Times that the past year "has been the most difficult and painful year of my career. It was excruciating."

Why it matters: Beyond providing a window into Musk's state of mind, the article provides updates into Tesla's inner workings and the take-private announcement that's under investigation by securities regulators.

A few takeaways...

• One plan under consideration is to have another Musk company, SpaceX, help finance the take-private plan and take an ownership stake in Tesla.
• Tesla board members and Musk could meet with SEC officials as soon as next week.
• "Efforts are underway" to find a number 2 executive to ease pressure on Musk, the paper reports, citing sources briefed in the search.
• However, Musk tells the paper that while the company approached Facebook COO Sheryl Sandberg a couple years ago, he says that “to the best of my knowledge,” there is “no active search right now.”

Go deeper: Read the full story in the Axios stream.