Enlarge (credit: Frame Studio )

Almost from the start, arguments about mitigating climate change have included an element of cost-benefit analysis: Would it cost more to move the world off fossil fuels than it would to simply try to adapt to a changing world? A strong consensus has built that the answer to the question is a clear no, capped off by a Nobel in Economics given to one of the people whose work was key to building that consensus.

While most academics may have considered the argument put to rest, it has enjoyed an extended life in the political sphere. Large unknowns remain about both the costs and benefits, which depend in part on the remaining uncertainties in climate science and in part on the assumptions baked into economic models.

In Wednesday's edition of Nature, a small team of researchers analyzed how local economies have responded to the last 40 years of warming and projected those effects forward to 2050. They find that we're already committed to warming that will see the growth of the global economy undercut by 20 percent. That places the cost of even a limited period of climate change at roughly six times the estimated price of putting the world on a path to limit the warming to 2° C.

Enlarge / Each panel shows the modeled effects of early Earth’s bombardment. Circles show the regions affected by each impact, with diameters corresponding to the final size of craters for impactors smaller than 100 kilometers in diameter. For larger impactors, the circle size corresponds to size of the region buried by impact-generated melt. Color coding indicates the timing of the impacts. The smallest impactors considered in this model have a diameter of 15 kilometers. (credit: Simone Marchi, Southwest Research Institute)

When it comes to space rocks slamming into Earth, two stand out. There’s the one that killed the dinosaurs 65 million years ago (goodbye T-rex, hello mammals!) and the one that formed Earth’s Moon . The asteroid that hurtled into the Yucatan peninsula and decimated the dinosaurs was a mere 10 kilometers in diameter. The impactor that formed the Moon, on the other hand, may have been about the size of Mars. But between the gigantic lunar-forming impact and the comparatively diminutive harbinger of dinosaurian death, Earth was certainly battered by other bodies.

At the 2023 Fall Meeting of the American Geophysical Union, scientists discussed what they’ve found when it comes to just how our planet has been shaped by asteroids that impacted the early Earth, causing everything from voluminous melts that covered swaths of the surface to ancient tsunamis that tore across the globe .

Modeling melt

When the Moon-forming impactor smashed into Earth, much of the world became a sea of melted rock called a magma ocean ( if it wasn’t already melted ). After this point, Earth had no more major additions of mass, said Simone Marchi , a planetary scientist at the Southwest Research Institute who creates computer models of the early Solar System and its planetary bodies, including Earth. “But you still have this debris flying about,” he said. This later phase of accretion may have lacked another lunar-scale impact, but likely featured large incoming asteroids. Predictions of the size and frequency distributions of this space flotsam indicate “that there has to be a substantial number of objects larger than, say, 1,000 kilometers in diameter,” Marchi said.

Enlarge / Modeling has shown how material ejected from the Earth by a massive collision could have formed the Moon. Now the models are being used to look at what happened inside the Earth. (credit: NASA )

Seismic waves created by earthquakes as they travel through the planet's interior change speed and direction as they move through different materials. Things like rock type, density, and temperature all alter the travel of these waves, allowing scientists to gradually build up a picture of the Earth's crust and mantle, spotting things like the rise of plumes of hot mantle material, as well as the colder remains of tectonic plates that dropped off the surface of the Earth long ago.

There are some things that show up in these images, however, that aren't easy to explain. Deep in the Earth's mantle there are two regions where seismic waves slow down, termed large low-velocity provinces. This slowdown is consistent with the materials being higher density, so it's not really a surprise that they're sitting near the core. But that doesn't explain why there are two distinct regions of them or why they appear to contain material that has been there since the formation of the Solar System.

Now, a team of scientists has tied the two regions' existence back to a catastrophic event that happened early in our Solar System's history: a giant collision with a Mars-sized planet that ultimately created our Moon.

Enlarge (credit: MARK GARLICK/SCIENCE PHOTO LIBRARY )

Classic whodunit mysteries work because just about every character ends up being a murder suspect. The demise of non-avian dinosaurs is a lot like that. The Chicxulub impact and its aftereffects created a huge range of potentially lethal suspects. Whodunit? A giant fireball and massive tsunamis? Wild swings in the climate? Global wildfires? A blackened sky that shut down photosynthesis? All of the above?

Modeling these impacts, combined with data on the pattern of extinctions, has led to various opinions on what proved decisive regarding the extermination of so many species. In the latest look at the end-Cretaceous extinction, a team of scientists largely based in Brussels has revisited deposits laid down in the aftermath of the impact and found that much of the debris came from fine dust. When that dust is plugged into climate models, global temperatures plunge by as much as 25° C, and photosynthesis shuts down for almost two years.

Dust to dust

There was a lot going on in the atmosphere in the years after the impact. Debris thrown up by the impact would have re-entered Earth's atmosphere, burning up into fine rocky and sulfur-rich particles in the process. The heat generated by this process would have set off massive wildfires, adding a lot of soot to the mix. And all of that was churned up with the debris from the impact that stayed within the atmosphere.

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 / Annapurna IV, at left here, might have once been half a kilometer taller. (credit: Richard I'Anson )

The Earth's mountains are engaged in a constant balancing act. Tectonic forces—a combination of volcanism and plate collisions—push them skyward. But erosion pulls them down. The height of the tallest peaks is set by which of these forces dominate.

When it comes to erosion, ice can be a dominant factor. Glaciers scrape away rock, while freeze/thaw cycles crack it. But a new paper suggests that ice has a limited effect on the very tallest peaks. At those altitudes, the freeze/thaw cycle shuts down because things remain cold year-round. And most peaks are steep enough that glaciers never have the chance to form. (They're mostly a kilometer or more below the peaks, down in the valleys).

Instead, the new paper argues that the tallest mountains don't so much erode as collapse, producing utterly massive landslides that can be catastrophic many miles downslope. To make this case, the paper presents evidence from a landslide involving 20 cubic kilometers of material in the Annapurna region of Nepal.

Enlarge (credit: NASA )

When Tonga’s underwater Hunga Tonga volcano lost its temper in an eruption on January 15, 2022, it belched gobs of magma and exhaled clouds of ash and water vapor out of the ocean, triggering intense lightning . This was no ordinary thunderstorm.

Hunga is infamous for its tantrums, but it has outdone itself. That storm now boasts the most lightning ever recorded on Earth. Hanging ominously above the Pacific Ocean was a volcanic cloud lit by concentric rings of lightning that flashed about 192,000 times over the 11 hours that the volcano was active (that’s some 2,615 flashes a minute). Lightning shot up to 30 km (19 miles) high—another record, beating even cyclones and supercells.

Led by volcanologist Alexa Van Eaton of the US Geological Survey, a team of researchers who took a closer look at the observations from the Hunga eruption and ensuing storm found that no one has ever recorded lightning so extreme. “Our findings show that a sufficiently powerful volcanic plume can create its own weather system, sustaining the conditions for electrical activity at heights and rates not previously observed,” Van Eaton and her team said in a study recently published in Geophysical Research Letters.

Enlarge / A Voyager-class saildrone. (credit: Saildrone)

Science fiction often paints a terrifying picture of the future—think aliens decimating humanity, à la The War of the Worlds . But sometimes the future becoming the present can be pretty amazing—who doesn’t love successful space launches majestically catapulting humans skyward?

Or take Earth’s oceans, which are currently in the middle of a technological revolution that, outside of some very nerdy circles, has gone largely unnoticed.

“We’re at the cusp of a proliferation of lots of autonomous vehicles in the ocean,” said Alex De Robertis , a biologist at the Alaska Fisheries Science Center of the National Oceanic and Atmospheric Administration (NOAA). “Things that were science fiction not so long ago are kind of routine now.” That includes saildrones, which look like oversized orange surfboards, each with a hard, carbon-fiber sail (called a wing) and a stash of scientific equipment.