Runaway Greenhouse Effect On Venus Foreshadows Earth's Climate Disaster
By Tim Radford
There is already a runaway greenhouse effect on the planet Venus: all the oceans have boiled away, the clouds rain sulphuric acid and the atmosphere at ground level is hot enough to melt lead. The only comfort is that if such a transformation does affect the Earth, it probably won’t be for a billion years or so.
Colin Goldblatt of the University of Victoria in Canada and U.S. colleagues report in Nature Geoscience that they have been taking a new cool look at what makes one terrestrial planet temperate and stable and the other so hot that the ocean boils away, and the answer is disconcerting. Both outcomes are possible for a planet that receives the same level of solar radiation as the Earth does today.
“A runaway greenhouse could in theory be triggered by increased greenhouse forcing, but anthropogenic emissions are probably insufficient,” the authors say, comfortingly.
The Goldilocks Planet
The research grows out of a continuing academic interest in the unusual condition of planet Earth—just far enough from the Sun for water to freeze but near enough for some of it to melt and evaporate, massive enough to retain an atmosphere and clouds of water vapor but small enough for a gravitational pull that will allow complex creatures to evolve, grow tall and even fly. Goldilocks, the girl in the British fairy story, chose the porridge that was not too hot, not too cold, but just right, and planetary scientists have co-opted the imagery, and dubbed the Earth the Goldlilocks planet.
But global warming fueled by carbon dioxide (CO2) emissions from the burning of fossil fuels is a warning that “just right” might not be a permanent condition, and environmental campaigners have frequently warned of the dangers of a runaway greenhouse effect—in which an increasingly warmer world means greater and greater releases of trapped carbon and methane, until the process becomes unstoppable. Until the Nature Geoscience paper, the assumption was that such a process was unlikely: a Venus-style runaway warming would require more solar radiation than the Earth actually gets.
Clouds Make the Difference
But while carefully considering the factors that make Earth such a desirable residence—fully air-conditioned and with hot and cold running water—Goldblatt and his colleagues found a puzzle. Their numerical models calculated the balance between solar radiation absorbed and thermal radiation emitted and found that the sunshine levels on Earth now would actually make a runaway greenhouse possible.
What makes the difference right now are the clouds, which serve to reflect radiation back into space and which eventually condense and return evaporated water to the land and then the oceans. But water vapor is also a greenhouse gas, so as long as the vapor forms clouds that provide what engineers call negative feedback, and damp down the warming, the temperatures stay within manageable limits. But the logic is that with greater levels of greenhouse gases—and with fewer clouds—conditions could change, the atmosphere would become steamier, ever more heat would be retained and eventually life would become impossible.
But there has never been a runaway greenhouse on Earth—it would have sterilized the planet and life would never have emerged at all—and the planet has been at least 10 degrees Celsius hotter during the Eocene 50 million years ago, when CO2 levels were much higher.
“With CO2 and temperature both higher then than we expect in the foreseeable future, this implies that an anthropogenic runaway greenhouse is unlikely,” the authors conclude.
But they also warn that Venus today is a reminder of what the Earth could become, and they expect a runaway greenhouse on Earth in about 1.5 billion years “if water is the only greenhouse gas, or sooner if there are others.”
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Sweden's reindeer have a problem. In winter, they feed on lichens buried beneath the snow. But the climate crisis is making this difficult. Warmer temperatures mean moisture sometimes falls as rain instead of snow. When the air refreezes, a layer of ice forms between the reindeer and their meal, forcing them to wander further in search of ideal conditions. And sometimes, this means crossing busy roads.
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By Aaron W Hunter
A chance discovery of a beautifully preserved fossil in the desert landscape of Morocco has solved one of the great mysteries of biology and paleontology: how starfish evolved their arms.
The Pompeii of palaeontology. Aaron Hunter, Author provided<h2></h2><p>Although starfish might appear very robust animals, they are typically made up of lots of hard parts attached by ligaments and soft tissue which, upon death, quickly degrade. This means we rely on places like the Fezouata formations to provide snapshots of their evolution.</p><p>The starfish fossil record is patchy, especially at the critical time when many of these animal groups first appeared. Sorting out how each of the various types of ancient starfish relate to each other is like putting a puzzle together when many of the parts are missing.</p><h2>The Oldest Starfish</h2><p><em><a href="https://www.biorxiv.org/content/10.1101/216101v1.full.pdf" target="_blank" rel="noopener noreferrer">Cantabrigiaster</a></em> is the most primitive starfish-like animal to be discovered in the fossil record. It was discovered in 2003, but it has taken over 17 years to work out its true significance.</p><p>What makes <em>Cantabrigiaster</em> unique is that it lacks almost all the characteristics we find in brittle stars and starfish.</p><p>Starfish and brittle stars belong to the family Asterozoa. Their ancestors, the Somasteroids were especially fragile - before <em>Cantabrigiaster</em> we only had a handful of specimens. The celebrated Moroccan paleontologist Mohamed <a href="https://doi.org/10.1016/j.palaeo.2016.06.041" target="_blank" rel="noopener noreferrer">Ben Moula</a> and his local team was instrumental in discovering <a href="https://www.sciencedirect.com/science/article/abs/pii/S0031018216302334?via%3Dihub" target="_blank" rel="noopener noreferrer">these amazing fossils</a> near the town of Zagora, in Morocco.</p><h2>The Breakthrough</h2><p>Our breakthrough moment came when I compared the arms of <em>Cantabrigiaster</em> with those of modern sea lilles, filter feeders with long feathery arms that tend to be attached to the sea floor by a stem or stalk.</p><p>The striking similarity between these modern filter feeders and the ancient starfish led our team from the University of Cambridge and Harvard University to create a new analysis. We applied a biological model to the features of all the current early Asterozoa fossils in existence, along with a sample of their closest relatives.</p>
Cantabrigiaster is the most primitive starfish-like animal to be discovered in the fossil record. Aaron Hunter, Author provided<p>Our results demonstrate <em>Cantabrigiaster</em> is the most primitive of all the Asterozoa, and most likely evolved from ancient animals called crinoids that lived 250 million years before dinosaurs. The five arms of starfish are a relic left over from these ancestors. In the case of <em>Cantabrigiaster</em>, and its starfish descendants, it evolved by flipping upside-down so its arms are face down on the sediment to feed.</p><p>Although we sampled a relatively small numbers of those ancestors, one of the unexpected outcomes was it provided an idea of how they could be related to each other. Paleontologists studying echinoderms are often lost in detail as all the different groups are so radically different from each other, so it is hard to tell which evolved first.</p>
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