With a rapidly warming planet, the need to better understand the nature and long-term impact of positive climatic feedback loops becomes critical.
Modeling studies can be used to look into the future based on what we know at the moment. Climate projection models are used to calculate the 1.5 C global warming threshold.
Look into the past to see what happened when the Earth was up to 1.5C warmer. In a paper published in the Proceedings of the National Academy of Sciences, weldeab did that. The professor of paleoclimatology found feedback processes that have implications for our current climate.
Weldeab and his colleagues went back some 128,000 to 125,000 years ago to see the peak of the Eemian warm episode. The oceans were up to 1.5 degrees warmer. During the peak Eemian warm episode, the authors found extremely strong warming of the intermediate water column in the tropics.
Weldeab said that the diminished ice sheet was capable of producing enough meltwater to perturb the circulation of the ocean. The warming of the intermediate waters was a result of this.
Warm, salty water travels north from the tropics along the surface of the ocean and cools in the high latitudes. The denser water goes back to the tropics at this point. Density differences result in currents that we're familiar with.
When you put a lot of fresh water into the North Atlantic, it disturbs ocean circulation and reduces the flow of cold water into the tropical Atlantic, which warms the waters at this depth.
The new paper shows that the disruption that meltwater caused to currents and temperatures was larger than previously thought.
Weldeab said that they showed a hitherto undocumented and remarkably large warming of water at intermediate depths.
There is a mixture of frozen water and methane in the marine debris caused by the warm water. The deposits are close to the surface of the ocean.
The introduction of warm water at high pressure and low temperatures causes the ice-encapsulated gases to start dissolving. In order to find the fingerprints of methane release and methane oxidation across the water column, Weldeab and colleagues used carbon atoms in the shells of microorganisms.
He said that a warming climate caused the ice sheet to melt. The meltwater weakened the ocean circulation, and as a result, the waters at intermediate depth warmed, leading to the destabilization of shallow methane hydrates and the release of methane, a potent greenhouse gas.
It is not known if this feedback cycle will play out in the current round of global warming, as the rate of warming in the Eemian period was lower than it is today. According to the researchers, the findings show a sequence of climatic events and climatic feedback processes associated with and triggered by the final peak of climate warming.
Weldeab said that paleo perspective is a useful approach. Every situation is different but it gives you a direction where to look.
More information: Syee Weldeab et al, Evidence for massive methane hydrate destabilization during the penultimate interglacial warming, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2201871119 Journal information: Proceedings of the National Academy of Sciences
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