Enlarge / Some of the ice near the South Pole of Mars stays around all year long.NASA/JPL-Caltech/Univ. of Arizona
Mars is a vast, frozen desert. Nowhere is that more evident than at its poles, which are the coldest regions on the planet. However, it looks like the weather forecast for its harsh winters and slightly more forgiving springs could be different from we thought.
Like Earth, Mars has a volatile cycle that sees snow and ice levels fluctuate as temperatures plummet in the winter and start to rise again in the spring. Unlike Earth, Martian snowfall includes CO2 snow and is influenced by different phenomena. Now, a team of researchers led by Haifeng Xiao of Berlin Technical University in Germany is reexamining the change in snowfall over the course of a year at the Martian north pole. Their findings suggest that forces such as sublimation might mean there is more snow in the winter—and less in the spring—than previously thought.
“We propose to use the shadow variations [of ice blocks] to infer the seasonal depths at high polar latitudes,” Xiao and his team said in a draft manuscript recently published in the Earth and Space Science Open Archive.
Not like Earth
How snow accumulates on Mars may seem alien compared to the way it happens on Earth. The composition of Martian snow explains why it can snow in regions on Mars where conditions would make it nearly impossible for snow to form here on our planet. Earth snowfall requires the presence of atmospheric water, which is why frigid but otherwise dry areas do not see much of the white stuff. While water ice and snow exist on Mars, dry areas may still experience a buildup of CO2 snow and ice. Frozen carbon dioxide sublimates instead of melting when it gets too warm. Therefore, both sublimation and evaporation influence how much snow and ice buildup there is on Mars during a given season.
There are other phenomena affecting Martian snow and ice accumulation that do occur on Earth but are still different on Mars. Katabatic winds, which arise from the sinking of cold air that then spirals furiously across the ice, are found at the poles on Earth, but they have twice to three times the strength on Mars. This is due largely to the red planet’s extremely thin atmosphere. On Mars, katabatic winds also affect larger regions than they do on Earth, blowing huge troughs of ice and snow that can be up to 10 km (about 6.2 miles) wide and 1 km (about .62 miles) deep.
Still, some of the ways that ice and snow accumulate on Mars mostly mirror effects on Earth. Solar heat becomes stored in regolith below the snow and ice during the summer, and snow around a large rock will vanish as late as the fall because so much heat is still retained by the rock. Though moating (the empty space where the snow once was appears like a moat around the rock) generally happens the same way as it does on our planet, the difference on Mars is that ice and snow usually sublime from the warm area as opposed to melting and evaporating on Earth. Crowning ice caps, which form over rocks in the winter after heat has escaped from the underlying rock, can also be found on Earth.
Xiao and his team wanted to estimate the overall accumulation of snow and ice on the Martian north pole and compare their estimate to previous observations from NASA’s MOLA (Mars Orbiter Laser Altimeter) spacecraft. They tested for the depth of seasonal deposits of snow by measuring the shadows cast by ice blocks in the North Pole Layered Deposits, as seen in hi-res NASA HiRISE (High Resolution Imaging Experiment) images. As temperatures changed over the course of a Martian year, or sol, these deposits would evolve, and so would their shadows. Snowfall and depth predictably decreased from winter to spring.
Peak accumulation
What was less predictable was the amount of snow and ice present at certain times. “The large snow depth measured makes us wonder if snowfalls are more frequent and violent than previously thought,” Xiao and his team said in the same study, later stating that snow in the later years studied was deeper than expected.
There were some obstacles. Ice crowns did sometimes get in the way, as they made ice blocks and snow-covered rocks thicker, which meant they cast longer shadows. The absence of snow in moats around rocks reduced shadows and also had to be corrected for. Overall, uncertainties were less than a meter (about three feet)—which is substantial given the amount of snow that fell.
So how much snow can we expect on Mars each year? At its highest, the thickness of Martian snowfall is close to a meter in winter, decreasing to .21 m (about .7 foot) in spring and continuing to drop throughout summer until colder weather sets in. Snowfall contributes significantly more to total accumulation than frosts that directly condense on the surface.
While the snowfall on Mars would have easily made for many snow days (at least before the Internet made remote school common), Xiao thinks that further study of the variations of snow and ice depth on Mars may someday reveal more about the planet’s often mysterious insides. The snow still has secrets to tell.
EnlargeLuis Sinco/Los Angeles Times/Getty Images
The global temperature numbers for September are in, and they are not good. “This month was, in my professional opinion as a climate scientist—absolutely gobsmackingly bananas,” Zeke Hausfather posted Tuesday on X (formerly known as Twitter).
Kristina Dahl, principal climate scientist at the Union of Concerned Scientists, read that post yesterday. “I've been sitting at my desk trying to think of a better way to describe that, but I can't,” Dahl says. “It's just shocking.”
“Concerning, worrying, wild—whatever superlative you want to use,” says Kate Marvel, senior scientist at Project Drawdown, a nonprofit that fights climate change. “That's what it is.”
The graph below, created by Hausfather, a researcher at the climate group Berkeley Earth, shows temperature anomalies, meaning how high each month was above a historical average baseline temperature. Each multicolored line represents a previous year, color coded by decade. (The 1990s, for example, are the lines in yellow.) The solid black line is 2023, and it has been soaring above the others since May. It stops in the month of September, which beat the prior monthly record by more than 0.5° Celsius.
This September was on average 1.8° C hotter than preindustrial levels, well above the Paris Agreement’s goal of keeping temperatures from rising more than 1.5° C. (Important caveats on that in a moment.)
EnlargeZeke Hausfather
“We've already seen a summer of extreme temperatures, so my threshold for being surprised was a bit higher,” Hausfather tells WIRED. “But just how extreme September was, it's kind of bananas; 0.5° C is just off the charts. We’ve never seen a month with that level of jump before.”
“It's astounding to see the previous record broken by so much,” agrees Dahl. “And astounding to see that the global temperature this September is on par with what we normally see in July—the hottest month of the year, typically. So it really just illustrates how profoundly our climate is shifting.”
What’s unfolded all summer has been a mixture of climate science factors, some of which are well understood and others that are more uncertain. It’s a certainty that the more greenhouse gases we pump into the atmosphere, the more warming we get. “We should expect not just record-breaking extremes, but record-shattering extremes,” says Marvel. “Things that break previous records by incredible margins.”
A little bit of uncertainty—along with some extra heat—is being injected into the process right now by El Niño, the band of warm water that forms in the Pacific Ocean off the coast of South America. Typically, that phenomenon can add a couple tenths of a degree Celsius by transferring heat from the oceans to the atmosphere. The exact effects or arrival date of El Niño can be unpredictable—and this one is still developing. But it’s a cyclical natural process, so climate scientists are used to working it into their calculations.
“Then you get in the realms of things that yeah, sure, they probably have an effect, but I don't think we've done the sort of really rigorous science to quantify them,” says Marvel. For one, scientists are investigating whether new regulations have had a weird side effect for the climate. In 2020, the International Maritime Organization dramatically limited the amount of sulfur in shipping fuel. That was great for reducing air pollution, but that sulfur had actually been brightening the clouds over shipping lanes, bouncing some of the sun’s energy back into space. Less cloud cover could be helping raise temperatures.
Last year’s massive Hunga Tonga volcanic eruption may also still be having a small warming influence. Volcanoes can cool the climate dramatically by firing aerosols into the atmosphere and blocking the sun. But not Hunga Tonga. “Because it was so big, and because it was underwater, it put a bunch of water vapor in the stratosphere,” says Marvel. Water vapor is actually a planet-warming greenhouse gas. “This might have had a slight warming effect, but we're talking less than a tenth of a degree. But added on to everything else that's going on, that could be a factor.”
All of these variables added up to September reaching 1.8° C above preindustrial levels. That does not mean, though, that we’ve blown through the Paris Agreement’s 1.5° limit. That goal represents sustained temperatures, not those for a single month.
Still, such extremes are alarming to scientists, both in terms of how quickly we’re approaching the Paris threshold and how gnarly the effects of climate change already are: fiercer rainfall, like the precipitation that flooded New York City in late September. More massive hurricanes, like this season’s Lee and Idalia. More vicious wildfires, like the one that obliterated Maui’s city of Lahaina in August. The proliferation of bacteria and fungi that thrive in a warmer world. Ever more extreme heat.
“This is not about our grandchildren, this is not about the polar bears, this is not about someplace far away. This is affecting us right now,” says Marvel. “What the science says is that every tenth of a degree matters. Every ton of emissions that can be avoided matters. If the world passes 1.5, then you shoot for 1.6. If it passes 1.6, you shoot for 1.7. And I think we now know after this year how 1.5 is not safe.”
This story originally appeared on wired.com.
