The Earth can react to huge amounts of carbon dioxide (CO2) that humans are pumping up the atmosphere, “over-correcting” the imbalance, which could result in the next ice age arriving on time rather than being delayed by tens of thousands of years as previously predicted.
It's linked to a new “thermostat” that is so effective at burying mountains of carbon beneath the seafloor that it could end human carbon emissions within 100,000 years, researchers have found.
If both thermostats work in tandem, it is possible that the next ice age could start on time rather than delayed due to climate change impactsco-author of the study Andy Ridgewellprofessor of geology at the University of California, Riverside, told Live Science.
New thermostat does not protect people living today from the effects of global warming, study co-author says Dominik Hulsemathematician and biogeochemical modeler at the University of Bremen in Germany. “That doesn't mean we'll be safe from global warming in the next 100 or even 1,000 years,” he told Live Science.
Scientists have long suspected that the Earth regulates its climate on geological time scales. Since the 1980s, researchers have theorized about a mechanism called silicate weathering feedback, which occurs when rain traps CO2.2 from the air and sprays it onto silicate rocks – rocks with oxygen and silicon minerals that make up about 90% planet's crust. CO2 reacts with these rocks, dissolving them and forming molecules that seep into the ground and eventually end up in the ocean. Where CO Once Was2 forms limestone and chalk, meaning it is locked away for millions of years.
The silicate weathering feedback is like a thermostat because the more CO2 that is, in the atmosphere, the Earth becomes warmer and the more the water cycle increases. As rainfall increases, silicate weathering accelerates, meaning more CO2.2 transported to the ocean and atmosphere by CO2 falls back to background levels.
Feedback works the other way around. “If you get too cold and CO2 too low, the thermostat consumes too little CO.2 compared to the background of constant CO emissions2 from the mantle, volcanoes and other igneous formations,” Ridgwell said. There is less CO in this scenario2 It ends up in the ocean and the atmosphere slowly returns to average levels, he said.
But silicate weathering feedback moves slowly; It may take up to 1 million years for the CO balance to recover after a disturbance.2 levels. As a result, there are climate phenomena that it cannot explain, including the Earth's glacial and interglacial cycles, which are characterized by huge fluctuations in CO2.2 levels and temperatures that occur approximately every 100,000 years, Ridgewell said.
Silicate weathering also cannot explain snowball earth eventswhich completely cover the planet in ice, Hulse said. If silicate weathering were the only thermostat regulating Earth's climate, its gentle balancing would prevent it from reaching such extreme conditions, Hulse explained.
Second “thermostat”
The new study was inspired Hulse's doctoral dissertationin which he calculated how much organic carbon was preserved in ocean sediments during past climate events. His results showed that after periods of intense volcanic activity and warming, mountains of organic carbon were deposited on the seafloor. This discovery suggests that there may be a connection between atmospheric CO2 ocean organic carbon levels and burial.
“There were definitely times in Earth's history when a lot of organic carbon was deposited,” Ridgewell said. “We kind of knew there were other things that had to happen. [besides silicate weathering]but implementing the model is much more difficult.”
But Hulse and Ridgwell solved this problem in a new study by combining their separate projects into a single model of the global climate carbon cycle that took into account the burial of organic carbon on the seafloor. Their findings revealed a second “thermostat” rooted in Earth's phosphorus cycle, which begins on land in rocks containing minerals such as apatite, the researchers said.
Weathering of these rocks due to precipitation releases phosphorus, which washes into the soil, flows into streams and rivers, and eventually ends up in the ocean. There, phosphorus is a key nutrient for tiny photosynthetic creatures known as phytoplankton, which use it to fuel cellular processes. When phytoplankton die, they sink to the ocean floor where they deposit organic carbon, phosphorus and other nutrients.
In a warmer world, more phosphorus washes into the ocean and phytoplankton thrive, meaning more organic carbon and phosphorus reaches the seafloor. However, warmer oceans also contain less oxygen because oxygen becomes less soluble as temperatures rise. As a result of deoxygenation, deposited phosphorus is released back into the water column, while organic carbon is buried in sediments.
“Exactly how this happens is not entirely known from a mechanistic point of view, but we know it happens,” Ridgwell said. “Where we've had events like this in the past where we've seen huge amounts of organic carbon buried after warming, this material had very, very, very little phosphorus in it compared to normal material. If it wasn't buried, it must have been returned to the ocean.”
As phosphorus is recycled, it reenters the food chain and phytoplankton continue to reproduce, feeding on phosphorus from both land and ocean. This leads to a boom of phytoplankton, which sucks up more and more CO2.2 from the atmosphere and deposits more and more organic carbon on the seafloor, lowering global temperatures.
So, the warmer the world gets, the more productive the oceans become and the more carbon is trapped, which cools the climate. But the difference between phosphorus and silicate weathering is that phosphorus in the ocean does not decrease as the Earth cools because it continues to be released onto the seafloor.
“An organic carbon thermostat is a bit like a silicate thermostat, except it has a blower,” Ridgewell said. “Eventually there are so many nutrients in the ocean—and they are processed very efficiently—that it is very difficult to get rid of them again.”
The phosphorus cycle eventually regains its balance, but the planet may “correct” in the meantime, causing events such as snowballing on Earth, the researchers say. It's unclear how this second thermostat will respond to climate change now, but the ocean is so rich in oxygen compared to the past that a snowball on Earth is unlikely, they say.
Instead, it is possible that the organic carbon thermostat compensates for the delay expected in the next ice age. Climate change is disrupting the Earth's natural cycles, and previous studies suggests this could push back the next ice age, which is about 11,000 years from now, by tens of thousands of years. But if the organic carbon thermostat is activated, atmospheric CO2 could return to background levels much faster, ensuring that the next ice age arrives on time.
“Whatever delay we experience in the next ice age… thinking about this mechanism could set it back again,” Ridgwell said. “You will definitely start someday, it all depends on when it starts.”
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