Archives par mot-clé : Oceanography

climate-debate, Cooling

Study: Greenland’s Melting Ice Unlikely To Trigger Atlantic Current’s Collapse

P. Gosselin, Apr, 10, 2025 in ClimateChangeDispatch 

Day after Tomorrow
We hear it again and again: the melting ice in Greenland due to global warming will soon lead to a collapse of the Gulf Stream system, with the result that it would be difficult to restart. [emphasis, links added]

Then we would see great disasters like those depicted in Roland Emmerich’s dramatic climate movie “The Day after Tomorrow”.

The seawater salinity in the north is critical because the salt-rich tropical water cools and sinks due to the higher salt content.

This acts as the pump that makes circulation possible in the first place. It serves to transport very large amounts of heat into the North Atlantic, keeping Europe on the mild side in the wintertime.

Scenarios have been published recently that calculate a drastic cooling of the large area (especially Europe) around it if the Gulf Stream system got “switched off”.

But those scenarios are proving to be overdramatic and alarmist.

Yuxin Zhou, a postdoctoral researcher in UC Santa Barbara’s Department of Earth Science, recently went back in history to study when the AMOC was severely weakened, from 68,000 to 16,000 years ago, when the Laurentide Ice Sheet existed and thick ice covered northern North America and even New York City.

Today, that massive ice shelf no longer exists and thus there is no longer the potential of an ice melt and iceberg release of that scale.

Very different, less dramatic circumstances today

By analyzing sea sediment deposited by floating icebergs in the North Atlantic, Zhou found that the AMOC heat-transferring oceanic current had already been moderately weakened before all the icebergs floated over the North Atlantic.

Comparing the situation to today, Zhou says, “In contrast, the circulation is very vigorous right now,” which suggests the melting of Greenland is not likely to plunge the North Atlantic into another deep freeze of the sort the alarmists fret about all the time.

Moreover, Technology Networks here adds (emphasis added):

Not all melting has the same effect on the Atlantic circulation. Freshwater released as icebergs has a much larger impact on the AMOC than runoff, which is released after melting on land. Icebergs can cool the surrounding seawater, causing it to freeze into sea ice. Ironically, this ice layer acts as a blanket, keeping the ocean surface warm and preventing it from plunging down to the depths and driving the Atlantic circulation. What’s more, icebergs travel much farther out to sea than runoff, delivering freshwater to the regions where this deepwater formation occurs.”

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unclassified

Understanding Abrupt Climate Change in the Late Quaternary

by R.S. Bradley & H.F. Diaz, Nov18,  2021 in Eos

Between about 75,000 and 10,000 years ago, there was a series of sudden and dramatic changes in rainfall patterns in tropical regions likely triggered by changes in ocean water circulation. A recent article in Reviews of Geophysics examines the evidence of these “Tropical Hydroclimatic Events” and explores the potential causes. Here, one of the authors explains more about these abrupt climate change events of the past and suggests how it can inform our understanding of potential future climate change.

What are “Tropical Hydroclimatic Events” (THEs)? When and where did they occur?

When we look back at past climate variations in continental regions of the Tropics and sub-Tropics (~30ºN-30ºS), it is abundantly clear that there were times when climate abruptly changed, causing some areas that were formerly wet to become quite dry, and areas that were formerly dry to become much wetter, disrupting plant and animal communities, as well as people living in the region. We call those changes “Tropical Hydroclimatic Events (THEs).” The changes affected vast areas (and lasted for centuries in some cases_ before the climate shifted back to the former conditions. There were at least half a dozen of these THEs between about 10,000 and 75,000 years ago.

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