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A new Nature paper outlines the relationship between rising temperatures and the literal rotation of the Earth.
Thinking too hard about time is a little like thinking too hard about blinking; it seems natural and intuitive until suddenly you’re sweating and it makes no sense at all. At least, that’s how I felt when I came across an incredible new study published in Nature this afternoon by Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography, suggesting that climate change might be affecting global timekeeping.
Our internationally agreed-upon clock, Coordinated Universal Time (UTC), consists of two components: the one you’re familiar with, which is the complete rotation of the Earth around its axis, as well as the average taken from 400 atomic clocks around the world. Since the 1970s, UTC has added 27 leap seconds at irregular intervals to keep pace with atomic clocks as the Earth’s rotation has gradually slowed. Then that rotation started to speed up in 2016; June 29, 2022, set a record for the planet’s shortest day, with the Earth completing a full rotation 1.59 milliseconds short of 24 hours. Timekeepers anticipated at that point that we’d need our first-ever negative leap second around 2026 to account for the acceleration.
But such a model doesn’t properly account for the transformative changes the planet is undergoing due to climate change — specifically, the billions of tons of ice melting from Greenland and Antarctica every year.
Using mathematical modeling, Agnew found that the melt-off, as measured by gravity-tracking satellites, has again decreased the Earth’s angular velocity to the extent that a negative leap second will actually be required three years later than estimates, in 2029.
While a second here or there might not seem like much on a cosmic scale, as Agnew explained to me, these kinds of discrepancies throw into question the entire idea of basing our time system on the physical position of the Earth. Even more mind-bogglingly, Agnew’s modeling makes the astonishing case that so long as it is, climate change will be “inextricably linked” to global timekeeping.
Confused? So was I, until Agnew talked me through his research. Our conversation has been edited and condensed for clarity.
How did you get involved in researching this? I’d never have expected there to be a relationship between climate change and timekeeping.
Pure accident. I’m a geophysicist and I have an avocational interest in timekeeping, so I know all about leap seconds and the history of atomic clocks. I thought about writing a paper figuring out statistically what the next century would bring in terms of leap seconds.
When I started working on the paper, I realized there was a signal that I needed to allow for, which was the change induced by melting ice — which has been studied, there are plenty of papers on this satellite gravity signal. But nobody has, as far as I can tell, related it to rotation. Mostly because, from a geophysical standpoint, that’s not very interesting.
Interesting. Or, well, I guess not interesting.
I mean, there is geophysical literature on this, but it’s largely, Okay, we see this signal, and gravity doesn’t mesh with what we think we know about ice melt. Does it measure what we think we know about sea level change? How does the geophysics all fit together? And the fact that it changes Earth’s rotation is kind of a side issue.
I did not know about this when I got started on this project; it appeared as I was working on it. I thought, “Wait, I need to allow for this.” And when I did, it produced the — I don’t want to use the words “more important” because of the climate change part, but it produced a secondary result, which was that this potential for a negative leap second became clear.
Walk me through how the ice melting at the poles changes the Earth’s rotation.
This is the part that’s easy to explain. Ice melts. A lot of water that used to be at the poles is now distributed all over the ocean. Some of it is close to the equator. The standard picture for what’s called change of angular velocity because of moment of inertia — ignore all the verbiage — but the standard picture is of an ice skater who is spinning. She has her arms over her head. When she puts her arms out, she will slow down — like the water going from the poles to the equator. And that’s it. This is the simple part of the problem.
So what’s the hard part?
The hard part is explaining the part about the Earth’s core. If you have two things that are connected to each other and rotating and one of them slows down, the other one has to speed up. I have not been able to think of an ice skater-like-metaphor to go with that, but the simple one is if you were to put a bowl of water on a lazy Susan and you spin the bowl, then the water will start to spin. It won’t spin initially, but then it will start.
If you started stirring the water in the other direction, that would slow the Lazy Susan down. And that’s the interaction between the core and the solid part of the Earth.
And is that causing the negative leap second to move back three years?
That’s why the leap second might happen at all. On a very long timescale, what’s happening is that the tides are slowing the Earth down. The Earth being slower than an atomic clock means that you need a positive leap second every so often. That was the case in 1972, when they started using leap seconds. The assumption was that the Earth would just keep slowing down and so there would be more positive leap seconds over time.
Instead, the Earth has sped up, entirely because of the core, and that’s not something that people necessarily anticipated. When you take the effect of melting ice out, it becomes clear there’s this steady deceleration of the core; the core is rotating more and more slowly. If you extrapolate that — which is a somewhat risky thing to do, you can’t really predict what the core is going to do — then you discover that there is a leap second, in 2029. The ice melting is going in the other direction; if the ice melting hadn’t occurred, then the leap second would come even earlier. Is this all making sense?
I think I’m grasping it.
Just so you know, one of the two reviewers of this paper was someone in geophysics who said, “I know all this stuff. I wasn’t familiar with the rotation part. This paper has an awful lot of moving parts.”
So, it’s just a difference of a second. Why does this even matter?
We are all familiar with the problem of not being synchronized — we just went through it. If you forget that we did Daylight Savings Time, then you’re an hour off from everybody else and it’s bewildering and a nuisance.
Same problem with leap seconds, except for us, a second is not a big deal. For a computer network, though, a second is a big deal. And why is that? Well, for example, in the United States, the rules for stock markets say that everything that is done has to be accurately timed to a 20th of a second. In Europe, it’s actually to the nearest 1,000th of a second. If we were all just farmers or something, it wouldn’t be a problem, but there’s this whole infrastructure that’s invisible to us that tells our phones what time it is, and allows GPS to work, and everything else.
The easiest thing to do would be to not have a negative leap second. Indeed, there are plans not to have leap seconds anymore because for computer networks, they’re an enormous problem. They arrive at irregular intervals; some human being has to put the information into the computer; the computer has to have a program that tells it when the leap seconds are; and most computer programs can’t tell whether it’s a plus or minus second because there’s never been a minus before. From the computer network standpoint, it would be simplest to just not do this.
So, you ask, why are we doing this? In 1972, when leap seconds were instituted, there were two communities that cared about precise time. One was the people who cared about the frequency of your radio station and other kinds of telecommunications. They wanted to use atomic clocks with frequencies that didn’t change, but that didn’t mesh with what the Earth was doing.
Who cares about time telling you how the Earth is rotating? Well, the answer then was that there were people who used the stars for celestial navigation. Back then, celestial navigation was used not just for ships, but for airplanes — if you flew across the ocean, there was a guy in the cockpit, an actual navigator, who would use a periscope to look at the stars and locate the plane, if only as sort of a backup system. That community is now gone. Almost nobody uses celestial navigation as a primary, or even a secondary, way of finding out where they are anymore because of GPS.
My own personal view — and I can warn you, there’s a huge amount of dispute about this — is that we’d be fine if we just stopped having leap seconds at all.
Is there a … governing body of time? That forces us to do leap seconds?
There’s a giant tangle of international organizations that deal with this, but the rules were set by the people in charge of keeping radio stations aligned because radio broadcasts were how time signals were distributed back in 1972. So the rule was created. Who makes that decision is something called the International Earth Rotation and Reference Systems Service, which uses astronomy to monitor what the Earth is doing. They can predict a little bit in advance where things are going to be, and if within six months things are going to be more than half a second out, they will announce there will be a leap second.
Back to climate change: It seems pretty amazing that something like melting ice can throw things off so much.
All the stuff about negative seconds is important, but it’s only important because of this infrastructure, because we have all these rules. Strip all of that away and the most important result becomes the fact that climate change has caused an amount of ice melt that is enough to change the rotation rate of the entire Earth in a way that’s visible.
How do you talk to people about the gigatons of ice that Greenland loses every year? Do you talk about “water that could cover the entire United States to the depth of X” to get it into people’s minds? Yes, these are small changes in the rotation rate, but just the fact that we can say, “Look, this is slowing down the entire Earth” seems like another way of saying that climate change is unprecedented and important.
How do we proceed, then, if climate change is messing with our system?
There was a lot of resistance to even introducing atomic time. Time was thought of as being about Earth’s rotation and the astronomers didn’t want to give it up. In fact, in the 19th century, observatories would make money by selling time signals to the rest of the community. Then, in the 1950s, the physicists showed up, ran atomic clocks, never looked at the stars, and said, “We can do time better.” The physicists were right. But it took the astronomical community a while to come around to accepting that was how time was going to be defined.
If we get rid of leap seconds then we’d really have cut the connection between the way in which human beings have always thought of time as being, say, from noon to noon, or from sunrise to sunset, and we’d be replacing it with some bunch of guys in a laboratory somewhere running a machine. For some people, it’s very troubling to think of severing the keeping of time from the Earth’s rotation.
You lose a bit of the romance, I think. But clearly, tying our way of describing the linear passage of sequential events to the Earth’s rotation is going to be messy.
Exactly right. There’s a quote from, of all people, St. Augustine, saying, “I know what time is, but if somebody asked me, I can’t tell them.”
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A little-noticed provision would make the payment option used by tax-exempt groups all but impossible to claim.
A little-noticed provision in the Senate tax bill will sabotage the efforts of tribes, rural electric cooperatives, and public power authorities to develop local affordable energy projects by striking a section of the Inflation Reduction Act that enabled tax-exempt groups to claim the clean energy tax credits as direct cash payments from the Treasury.
The IRA included strict domestic sourcing requirements beginning in 2026 for groups utilizing this “direct pay” option. But the law also created exceptions for cases where domestic components were not available in sufficient quantity or quality, or would increase costs by more than 25%. The Senate bill would get rid of these exceptions.
“It just makes it unlikely for those projects to go forward — or more likely for those projects to go forward with a private developer, instead of with a public utility or a tribe or a rural co-op,” Grace Henley, a tax attorney with the Natural Resources Defense Council, told me. “And so they don’t really do anything to increase the amount of domestic material that would be used, they just hurt the projects that are seeking to invest in clean energy infrastructure for these communities to lower costs.”
Public power and tribal energy advocates warn that without the exceptions, energy development will become impossible for their constituents.
Wind and solar projects being developed by these groups are already threatened by the bill’s rapid phase-out of wind and solar tax credits and its complex rules related to using materials from China. Chèri Smith, the executive director of the Alliance for Tribal Energy, told me that Tribes face longer development timelines than the average private developer. “We have multiple stages of approval that are unique to tribal energy development,” she told me, including lengthy internal consultation processes. The changes to direct pay will put these projects further out of reach, she said.
The Alliance provides free energy development consulting services to more than 100 Tribes. Smith sent me a list of projects in Alaska Native villages, Arizona, California, and Oregon that could be killed by the tax credit changes. “Alaska Native villages face some of the highest energy costs in the country,” she said, largely due to their reliance on diesel generators. Just over a third of the Hopi Tribe in Arizona lacks access to electricity, but now multiple microgrid projects meant to close the gap are at risk. Many of the projects on the list are also doubly threatened by grant cancellations and the repeal of the Tribal Energy Loan Guarantee Program.
“The bill is particularly harmful to Tribal Nations, pulling the rug out from under projects that would strengthen their energy sovereignty and power local communities,” Democratic Senators Martin Heinrich, Ron Wyden, and Brian Schatz wrote in a joint statement on Thursday. “Together, the Tribal Energy Loan Guarantee Program and our Inflation Reduction Act’s clean energy tax credits have cleared pathways and removed significant barriers for Tribes to finance and build their own resilient energy infrastructure.”
The American Public Power Association is also sounding the alarm. John Godfrey, the group’s senior government relations director, told me that in addition to wind and solar, municipal utilities and rural electric co-ops are also considering nuclear and hydropower projects. For example, Energy Northwest, a consortium of 29 public utilities in Washington State, has plans to retrofit the Columbia Generating Station nuclear plant to increase its power output. It’s also in early stages to deploy four small, modular nuclear reactors. As my colleague Matthew Zeitlin wrote a few days ago, the governor of New York has also tasked the New York Power Authority with developing a new nuclear plant in the state.
Nuclear and hydropower “are technologies where often there is not a U.S. source, but there is a good trading partner source — Canada, Germany, Japan,” Godfrey said. By tightening the domestic sourcing requirements for direct pay, the bill would “hinder the very technologies that there’s generally a bipartisan consensus we need to be developing.”
Public utilities and electric co-ops, which serve close to 30% of electric customers in the U.S., are also unfairly singled out by the provision, he said. “If my public power utility wants to develop a project and they need a Canadian turbine, they can’t get any credit. But if a taxable corporation down the street develops exactly the same project, they can.”
“If the purpose is to encourage hydropower, that’s not a good use of resources,” he said.
Senate Republicans tucked a carveout into their reconciliation bill that would allow at least one lucky renewable energy project to qualify for a major Inflation Reduction Act tax credit even after the law is all but repealed.
The only problem is, it’s near impossible to be sure right now who may actually benefit from this giveaway — and the mystery is driving me up the wall. I feel like Charlie Day in that episode of It’s Always Sunny in Philadelphia, stringing documents together and ranting like a lunatic.
The Senate bill would phase out the tech-neutral production tax credit starting next year and completely eliminate it by the start of 2028. For the past week and a half, I have been trying to solve the riddle of an exemption tucked into the language that would allow a wind or solar facility that is “part of a single project” to continue to take advantage of the tech-neutral production tax credit as it exists today, which means it would not begin to phase out until 2034.
To qualify for the exemption a project must, according to the Senate text, meet two conditions: It must produce more than 1 gigawatt of electricity, and be sited on federal lands where a “right-of-way grant or lease” had been given by the Bureau of Land Managementbefore June 16, which is the date the text was released.
Only a handful of projects in the U.S. could possibly fit that criteria. But every time I think I’ve identified one that will actually qualify, I learn a new fact that, to me, takes it out of the running.
Here’s why my head hurts so much: A renewables facility that would benefit from this language needs to be sited at least partially on federal lands. But because Trump isn’t issuing new right-of-way approvals or leases to most renewables projects right now, it likely had to get its right-of-way or its lease before he entered office. (The June 16 language feels like a bit of a red herring. Nothing that fits the other definitions has received these documents since the start of Trump 2.0.)
Then there’s another factor: The only projects that would benefit from this language are ones that haven't started construction yet. Even if a project doesn’t have all of its permits for federal land use, its developer can build stuff like roads on any connected private lands and technically meet the deadline to start construction laid out in the new legislation. The construction start date is what counts — it doesn’t matter whether a project is placed in service and provides power to the grid years later, as long as it began construction before that deadline.
Taken together, all this means that a project that would benefit from this language probably has to be sited on federal lands and hold permits already … but for some reason can’t start construction to qualify for the program.
When I first started hunting for an answer, many people — including renewables advocates, anti-wind activists, and even some Senate staff in conversations with me — speculated that the language was a giveaway to two wind projects under construction in Wyoming, Chokecherry and Sierra Madre, which together make up what would likely be the largest wind farm in the U.S. if completed. These two projects are largely sited on federal lands and received all their approvals before Trump entered office.
I understand why people are pointing at Chokecherry and Sierra Madre. They are not expected to be online before 2029, and the House version of the bill would have locked them out of the production tax credit because it added a requirement that projects be “placed in service” — i.e. actively providing power to the grid — by around that same period. Any slippage in construction might have really hurt their finances. They’re also backed by a powerful billionaire, GOP donor and live entertainment power-broker Phil Anschutz, a man who made his initial fortune partially from fossil fuels.
Except … my colleagues and I are still not convinced. That’s because it is not clear that these two projects are at any actual risk of losing the production tax credit. They have been actively under construction for a long time, and the Senate bill killed the House’s “placed in service” requirement.
Another project floated is the Lava Ridge wind farm in Idaho, which was fully permitted under Biden, is largely sited on federal lands, and would produce more power than necessary to qualify for the exception. Hypothetically, this project would be a great candidate for being a beneficiary of the bill because Trump banned work on the project via executive order amid opposition from Idaho politicians, making a carveout to get more time a worthwhile endeavor.
Except … Senate Finance Chair Mike Crapo, the lead author of the pertinent section of the Senate reconciliation bill, was one of those Idaho politicians who pushed Trump to kill Lava Ridge. Why would he give a tax break to a project he wanted dead?
Then there was my personal best guess for the beneficiary: Esmeralda 7, an expansive set of proposed solar farms in the Nevada desert that, as proposed, would produce more than 5 gigawatts of power and is largely sited on federal land. Construction can’t begin until Esmeralda 7 gets its federal approvals, and the Trump administration was expected to complete that work by mid-summer.
Except … I reported last week that the permitting process for Esmeralda 7 is now indefinitely stalled. The project is at best still months away from getting its right-of-way approvals from the Trump administration, which recently pushed back timelines for finishing reviews of other large Nevada solar projects, too.
Ultimately, it will be difficult to glean who the lobbyist giveaway here is for unless the legislators who wrote it disclose their intentions. I reached out to the communications director for Republicans on the Senate Finance Committee to try and find out, but so far I’ve gotten crickets.
It may be that this language is revised and that future changes lay out the true beneficiary. Sometimes lawmakers will put the wrong date or word into a bill and they’ll edit it on the floor before a vote, chalking it up to a drafting error.
If senators decide to add back the “placed in service” requirement to capitulate to the House, this would easily be the Chokecherry-Sierra Madre giveaway. If Republicans were to shift forward the deadline for getting a right-of-way, Esmeralda 7 would qualify. Or maybe they could change some secret third thing and a different project I hadn’t considered will be revealed as the mastermind in the shadows.
Until then, I’ll be in my basement poring over more maps and going slowly insane.
Additional reporting was provided by Emily Pontecorvo.
On resuming rare earth shipments, hurricane tracking, and EV tax credits
Current conditions: The Ohio Valley is still sweltering through the last remnants of this week’s brutal heat wave • The death toll from recent floods in South Africa has risen to 101 • It’s 90 degrees in Venice, Italy, where the world’s rich and famous are gathering for the wedding of Jeff Bezos and Lauren Sanchez.
The U.S. and China have hammered out the details of a trade deal, including an agreement that China will resume rare earth shipments to the U.S. Rare earth materials are essential for everything from planes to EVs to wind turbines. China controls most of the world’s rare earth production and halted exports in April in response to President Trump’s tariff hike, and China’s chokehold on rare earths threatened to derail trade talks between the two countries altogether. Commerce Secretary Howard Lutnick said a deal has now been “signed and sealed.” “They’re going to deliver rare earths to us,” Lutnick said, adding that the U.S. will then “take down our countermeasures.” Lutnick also indicated that Trump plans to announce further trade deals with other nations in the coming two weeks.
As climate talks in Bonn, Germany, wind down, negotiators there have agreed to increase the budget for the United Nations Framework Convention on Climate Change by 10% over the next two years to 81.5 million euros ($95.4 million). The UNFCCC runs some of the world’s largest climate negotiations and tries to ensure countries follow through on their climate commitments. Its budget is funded by government contributions. China will account for 20% of the new budget, Reuters reported. The U.S. is supposed to cover 22%, but President Trump has pulled international climate funding. Former New York Mayor Michael Bloomberg’s philanthropic arm has stepped in to cover the missing U.S. contributions. UN climate chief Simon Stiell said the budget increase was “a clear signal that governments continue to see UN-convened climate cooperation as essential, even in difficult times.”
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Hurricane forecasting is about to get a little bit more difficult. At the end of June, the federal government is going to stop distributing readings from the Defense Meteorological Satellite Program, a tool forecasters all over the world have been using to track and predict hurricane development. As retired federal meteorologist Alan Gerard told Bloomberg, this particular satellite program is unique because it lets forecasters peer inside storms and monitor for rapid intensification. As the planet warms, hurricanes are strengthening much faster than they did in recent decades. Hurricane expert Michael Lowry says the Department of Defense seems to be concerned that the satellite data poses a security concern. Its termination “will severely impede and degrade hurricane forecasts for this season and beyond, affecting tens of millions of Americans who live along its hurricane-prone shorelines,” Lowry wrote.
A group of U.S. car dealers penned a letter urging senators to “reject provisions in the budget reconciliation process that would abruptly eliminate EV-related tax credits from the Inflation Reduction Act,” warning that sudden changes would bring about market uncertainty, damage businesses, and hurt Americans. The signatories – including EV Auto, Carmax, and Caravan – instead call for a “gradual sunset” of the EV tax credits to avoid disruption to the used car market. “A multi-year transitional period would also provide the opportunity for Americans to continue adopting cleaner vehicles more affordably,” they add. The tax and budget bill put forward by Senate Republicans would end the $7,500 EV tax credit within 180 days after the law’s passage.
A report out today from the International Council on Clean Transportation estimates that the world’s private jets produced more greenhouse gas emissions in 2023 than all the flights that took off from Heathrow Airport — the world’s fourth busiest airport — that same year. Emissions from private jets increased 25% over the past decade. A few more interesting (though perhaps not surprising) tidbits from the report:
International Council on Clean Transportation
Solar power accounted for more than 10% of U.S. electrical output in April, while wind provided about 14%. As Michelle Lewis at Electreknotes, “solar is now producing more electricity than hydropower, biomass, and geothermal combined.”