Enlarge (credit: Marc Bruxelle )

"Climate breakdown has begun," declared UN Secretary-General António Guterres. Guterres is not a climate expert himself, but in this case, he's basing his opinion on the data and analyses generated by the actual experts. If you thought this year was a bit of a weather suffer-fest, it probably wasn't your imagination, as the Northern Hemisphere has just experienced its hottest summer on record, driving the year to date into the second-hottest position.

While the weather isn't climate, the climate sets limits on the sort of weather we should expect. And a growing number of analyses of this year's weather are showing that climate change has been in the driver's seat for a number of events.

Hot, hot, hot

On Wednesday, the World Meteorological Organization released its August data , showing that the month was the second hottest on record and the hottest August we have experienced since temperature records have been maintained. The only month that has ever been warmer is... the one immediately before it, July of 2023.

Enlarge / 2.7-billion-year-old basalt lava flows in the Pilbara Craton, now tilted about 45 degrees from horizontal. (credit: Jennifer Kasbohm )

Have tectonic plates changed speed over the last three billion years? The answer has far-reaching implications, as plate tectonics affected everything from the supply of vital nutrients for early life to the rise of oxygen . We know Earth’s interior was hotter early in its history, but did plates move faster because the hotter mantle was squishier, or did the hotter mantle contain less water , which helps mantle minerals flow, slowing plates down?

A new study , led by Dr. Jennifer Kasbohm of Yale, measured ancient magnetic fields and dated rocks from Western Australia to show that the “Pilbara Craton”—an early continent—moved at quite a clip around 2.7 billion years ago. While today’s fastest plate motion is around 12 cm (4.7 in) per year, the Pilbara Craton moved as much as 64 centimeters (25 inches) per year.

A rare remnant of early Earth

In the Archean eon, a time far closer to the formation of our Solar System than to today, basalt oozed over what would later be Western Australia in much the same way it does in Iceland and Hawaii today. Plate tectonics was still relatively new , and continents were in the early stages of emerging from what had largely been a water world . The air was devoid of oxygen, and the most advanced life came in the form of microbial communities that are preserved today in hummocky fossils known as “ stromatolites .”

Enlarge / Deployment of LSPM junction box 1. (credit: IN2P3/CNRS)

In 1962, one of the world's first underwater research laboratories and human habitats was established off the coast of Marseilles, France, at a depth of 10 meters. The Conshelf 1 project consisted of a steel structure that hosted two men for a week.

Now, more than 60 years later, another underwater laboratory is being set up not far from Marseilles, this time to study both the sea and sky. Unlike the Conshelf habitat, the Laboratoire Sous-marin Provence Méditerranée (LSPM) won't be manned by humans. Located 40 km off the coast of Toulon at a depth of 2,450 meters, it is Europe’s first remotely operated underwater laboratory.

Physics under the sea

Currently, three junction boxes capable of powering several instruments and retrieving data are at the heart of LSPM. The boxes, each measuring 6 meters long and 2 meters high, are connected to a power system on land via a 42-kilometer-long electro-optical cable. The optical portion of this cable is used to collect data from the junction boxes.

Enlarge / If this road is your only route to the outside world, it might not matter that your house didn't flood. (credit: Maurice Alcorn / EyeEm )

Climate change produces lots of risks that are difficult to predict. While it will make some events—heatwaves, droughts, extreme storms, etc.—more probable, all of those events depend heavily on year-to-year variation in the weather. So, while the odds may go up, it's impossible to know when one of these events will strike a given location.

In contrast, sea level rise seems far simpler. While there's still uncertainty about just how quickly ocean levels will rise, other aspects seem pretty predictable. Given a predicted rate of sea level rise, it's easy to tell when a site will start ending up underwater. And that sort of analysis has been done for various regions.

But having a property above water won't be much good if flooding nearby means you can't get to a hospital or grocery store when you need to or lose access to electricity or other services. It's entirely possible for rising seas to leave a property high, dry, but uninhabitable as rising seas cut connections to essential services. A group of researchers has analyzed the risk of isolation driven by sea level rise, and shows it's a major contributor to the future risks the US faces.

Enlarge / Is it natural, or is it us? (It's us.) (credit: Andriy Onufriyenko/Getty Images)

It starts as a reasonable question: If the Earth's climate changed before humans existed, how can we be so sure the current change is due to us and not something natural?

To answer that question, we need to understand what caused the natural changes of the past. Fortunately, science has a good handle on the causes of Earth’s natural climate changes going back hundreds of millions of years. Some were cyclical; others were gradual shifts or abrupt events, but none explain our changing climate today.

A zombie claim

With energy policy and elections in the news, the claim by some politicians that climate change is natural is once again bubbling up from the disinformation swamp. So I asked some scientists a very unscientific question: What would they buy if they had a dollar for every time they heard it?

Enlarge (credit: Simone Marchi/SwRI )

One of Earth's defining features is its plate tectonics, a phenomenon that shapes the planet's surface and creates some of its most catastrophic events, like earthquakes, tsunamis, and volcanic eruptions. While some features of plate tectonics have been spotted elsewhere in the Solar System, the Earth is the only planet we know of with the full suite of processes involved in this phenomenon. And all indications are that it started very early in our planet's history.

So what started it? Currently, two leading ideas are difficult to distinguish based on our limited evidence of the early Earth. A new study of a piece of Australia, however, argues strongly for one of them: the heavy impacts that also occurred early in the planet's history.

Options and impacts

Shortly after the Earth formed, its crust would have been composed of a relatively even layer of solid rock that acted as a lid over the still-molten mantle below. Above that, there was likely a global ocean since plate tectonics wasn't building mountains yet. Somehow, this situation was transformed into what we see now: The large regions of moving, buoyant crust of the continental plates and the constantly spreading deep ocean crust formed from mantle materials, all driven by the heat-induced motion of material through the mantle.

Enlarge / The massive trunk of a kauri tree can remain intact for tens of thousands of years. (credit: W. Bulach / Wikimedia )

The Earth's magnetic field helps protect life from energetic particles that would otherwise arrive from space. Mars now lacks a strong magnetic field, and the conditions on its surface are considered so damaging to life that any microbes that might inhabit the planet are thought to be safely beneath the surface. On Earth, the magnetic field ensures that life can flourish on the surface.

Except that's not always true. The Earth's magnetic field varies, with the poles moving and sometimes swapping places and the field sometimes weakening or effectively vanishing. Yet a look at these events has revealed nothing especially interesting—no obvious connections to extinctions, no major ecological upsets.

A paper published yesterday in Science provides an impressively precise dating for a past magnetic field flip by using rings of trees that have been dead for tens of thousands of years. And it shows the flip was associated with changes in climate. But the paper then goes on to attempt to tie the flip to everything from a minor extinction event to the explosion of cave art by our ancestors. In the end, the work is a mix of solid science, provocative hypothesizing, and unconstrained speculation.

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Enlarge (credit: Brunner et al./ESD )

One notable storyline in the climate system over the past year or two has been the effort to make sense of the latest generation of climate models. In service of the next Intergovernmental Panel on Climate Change (IPCC) report, the world’s climate models have submitted their simulations to the latest database, known as CMIP6 . These submissions showed that updates to a number of models had made them more sensitive to greenhouse gases, which means they project greater amounts of future warming.

Apart from diagnosing the behavior responsible for that change, climate scientists have also wrestled with the implications. Should we be alarmed by the results, or are they outliers? Climate models are only one tool among many for estimating Earth’s true “climate sensitivity,” so their behavior has to be considered in the full context of all the other evidence.

For a number of reasons, research is converging on the idea that the high temperature projections are outliers; these hotter models seem to be too hot. That will present a challenge for the scientists working on the next IPCC report: how much influence should these outliers have on projections of future warming?

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