More Evidence: The North Atlantic “Cold Spot” Human Caused

March 25, 2020

I’ve been following research on the North Atlantic Current (Scientists call it the Atlantic Overturning Meriodonal Circulation – AMOC) for some years.
New research underlining the climate connection to a slowing of that current has now been published.

Nature Communications:

North Atlantic sea surface temperatures have large climate impacts affecting the weather of the Northern Hemisphere. In addition to a substantial warming over much of the North Atlantic, caused by increasing greenhouse gases over the 21st century, climate projections show a surprising region of considerable future cooling at midlatitudes, referred to as the North Atlantic warming hole. A similar pattern of surface temperature trends has been observed in recent decades, but it remains unclear whether this pattern is of anthropogenic origin or a simple manifestation of internal climate variability. Here, analyzing state-of-the-art climate models and observations, we show that the recent North Atlantic warming hole is of anthropogenic origin. Our analysis reveals that the anthropogenic signal has only recently emerged from the internal climate variability, and can be attributed to greenhouse gas emissions. We further show that a declining northward oceanic heat flux in recent decades, which is linked to this surface temperature pattern, is also of anthropogenic origin.

EurekAlert:

Severe winters combined with heat waves and droughts during summer in Europe. Those were the consequences as the Atlantic Ocean heat transport nearly collapsed 12,000 years ago. The same situation might occur today, according to a new study published in Nature Communications.

Record-breaking cold ocean temperatures across the central North Atlantic in recent years suggest that the northward oceanic heat transport through the Atlantic Meridional Overturning Circulation (AMOC) has reached a long-term minimum and might be the weakest for at least 1,600 years. Most climate models project that the already observed slowdown will continue under global warming scenarios although a complete collapse appears unlikely – at least based on current models.

However, the climate history tells that we do not need to wait for a complete collapse to get a drastic climate response. A new study published in Nature Communications investigates how the strong cooling of the North Atlantic Ocean in response to a partial collapse of the AMOC impacted the European climate around 12,000 years ago. The period, called the Younger Dryas (YD), is the latest and one of the most extreme rapid cooling events that occurred during a phase of rapid warming at the climate transition from the late-glacial to our current warm climate, the Holocene. 

Although the last major climate shock in response to a partial collapse of the AMOC 12,000 years ago took place under quite different conditions, new climate model simulations emphasize a potentially worrisome analogy to today’s situation. First, the AMOC collapse takes place in response to a time of rapid warming. Second, while winters become extremely cold, our study shows that European summers might get even warmer. While warm summers do not sound bad, the mechanism leading to this additional warming is responsible for several of the worst heat waves and droughts in Europe. 

The simulation demonstrates that the mechanism behind this “cold-ocean-warm-summer” feedback is related to so-called atmospheric blocking. This blocking consists of high pressure systems which become quasi-stationary in their position for at least five days or even several weeks. These weather patterns are known to lead to extreme warming and drought in summer or extreme cold waves during winter. These high pressure systems cut Europe off from the warming westerlies in winter or the cooling westerlies in summer and cause the most extreme heat or cold waves. The simulation suggests now that a very cold North Atlantic leads to intensified atmospheric blocking 12,000 years ago and warm summers. The latter is confirmed by new geological evidence in the same study.

3 Responses to “More Evidence: The North Atlantic “Cold Spot” Human Caused”

  1. dumboldguy Says:

    Two of your best videos—-informative and clear. We are indeed “rats inside the experiment”. I’m sorry that I won’t live long enough to see how it turns out—it’s like putting a thriller novel down when you’re half way through—-you’ve seen all the groundwork laid, but won’t get to see how it turns out.

    • neilrieck Says:

      Depending upon how humanity holds our collective breaths on this COVID-19 thing, I wonder how long it will take before we see something in the monthly CO2 record from Mauna Loa. Remember that we saw immediate changes in cloud formation when most jet aircraft in the world was grounded (for up to three days) after 9/11.

  2. Sir Charles Says:

    Generally, we think of climate change as a gradual process: the more greenhouse gases that humans emit, the more the climate will change. But are there any “points of no return” that commit us to irreversible change?

    => Could the Atlantic Overturning Circulation ‘shut down’?


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