- Ocean temperatures keep setting all time highs.

But in the North Atlantic lies one very mysterious, very creepy exception.

It's called the cold blob or the warming hole.

And according to climate models, it shouldn't exist today, which means we're missing something.

So one researcher got to wondering, did the cold blob exist the last time the planet was this warm?

And if so, what happened after it appeared?

- Our study probably provides hints regarding our very near future.

- Mohamed is talking about Earth's most important heat transfer system.

The AMOC, an enormous ocean circulation that redistributes heat from the tropics and southern hemisphere into the northern latitudes.

And this global heat transfer is responsible for regulating weather that we rely on to function as a society, especially temperature and rainfall patterns.

And the appearance of the cold blob could mean that this vital earth system is on the brink of collapse, but it might not be so simple.

It turns out that there's a hot debate in the scientific community about the AMOC, and in this episode, we're going to get to the bottom of it because although there is debate, what most scientists agree on is that an amoc collapse will change our world dramatically.

- Once the climate warms enough, we can hit a tipping point where very suddenly and very catastrophically this AMOC current could collapse.

- The AMOC brings warm salty water from the Gulf to the North Atlantic, where it sinks bringing cold deep water as far as south as Antarctica.

This exchange keeps temperatures warmer in Europe and milder in the tropics.

But dramatic cooling in Europe probably isn't the biggest impact of an AMOC shift.

- I'm very worried about future changes in rainfall and water availability.

During times when the AMOC is strong, the northern hemisphere tropics and monsoon regions are generally stronger and wetter.

- This, scientists say, is because the AMOC influences the Intertropical Convergence Zone, which is the belt where trade winds meet forming regions of heavy seasonal rain on either side of the equator known as monsoons.

It's really hard to imagine how many people a sudden shift in monsoons would impact - Over half the world's population are impacted by them.

And so really understanding how those could potentially change is really critical.

- That's because as the AMOC slows, the northern hemisphere cools, that cooling shifts the tropical rain bands south and the monsoons effectively miss regions that count on them for up to 90% of their yearly precipitation directly impacting food security for over 2 billion people.

So with so much on the line, what does the scientific community say?

- There are a number of studies that really suggest that the risk is much larger and much closer actually with lower levels of warming than we have previously thought.

- Most models do predict an AMOC weakening before the end of the 21st century, some by up to 46%, even in low greenhouse gas emission scenarios, and 55% for high emission scenarios.

And some find a collapse by mid-century is possible, or even likely.

So that's just a few decades away.

But there are also scientists at very reputable institutions who declined our interview requests on the subject because they don't believe there is convincing evidence that the current is weakening.

So what's going on here?

Well, the AMOC is hard to study.

It's variable from year to year.

So even though a slight slowdown has been observed in the last two decades, when scientists began directly observing the current, there isn't enough data to determine a trend.

And even this slowdown isn't particularly clear.

But there is a third way to study the AMOC, and that's by looking at paleo climate data or the study of earth's past climate.

- Paleo climate, in my view, is really critical to understanding the future of Earth's climate because humans have only been recording climate with instruments and satellites for decades to maybe a couple of centuries at most.

- Using clues buried in snow, ice, marine sediment, and one very unexpected place, which we'll get to in a bit.

Researchers can put together an incredible history of earth's past climate by literally measuring cores of the earth.

But getting the data for paleoclimate research is easier said than done.

We visited a scientist at Oregon State University who studies ice cores found miles below the surface.

- This sample came from about a mile deep in the Greenland ice sheet.

- Since ice is so thick, there are thousands of samples that have to be measured and all of them are cut by hand.

Once the ice is cut, it's taken to the lab where each sample is measured.

- After we cut the ice samples, we put 'em in a little flask.

That flask is mounted to our our vacuum line, and we pump out all the air.

We close it off and we melt the ice.

- Christo is measuring the methane concentration in these ice samples, trying to understand past AMOC collapses.

To do this, the ice sample is refrozen so that the ice is at the bottom and the air is at the top.

He then measures that air.

- Once we find the methane spike, we know exactly where we are in time.

- By cross-referencing paleo climate records, scientists are able to confidently reconstruct past climate events.

- There's a one-to-one relationship between all these different things, greenhouse gases, temperature and Antarctica, temperature in Greenland, rainfall in the tropics.

When the current is on, we know that the monsoons in India and and China are very strong.

This means there's gonna be more wetlands in those places, and wetlands are exactly the thing that produce methane.

That's the relationship between methane and this AMOC current, it runs through the monsoons, - Which brings us to caves, the best way to study the Earth's past hydro climate.

- Primarily we use stalagmites in our research.

They form on the cave floor as water's dripping, precipitating calcite layer by layer.

So you get these really beautiful long stalagmites that are effectively a history of groundwater chemistry.

- By measuring oxygen isotope ratios, which tell scientists the past temperature and rainfall conditions, Kathleen is able to see abrupt shifts in rainfall patterns.

This allows her and other scientists to understand AMOC impacts and reconstruct past climate events like an AMOC slowdown or collapse.

Earth has two major modes: glacial and interglacial periods.

Currently we are in an interglacial period with a warmer, more stable climate.

But looking at the last ice age, which is the last glacial period, may actually foreshadow what's coming our way.

- One of the reasons we're so concerned about these potential collapse of the AMOC is that we actually have examples of it.

During the last ice age, we have at least 25 examples where the AMOC actually collapsed.

- 25 different collapses during the last ice Age is an average of once every 5,000 years.

So according to Earth's paleoclimate record, an AMOC collapse in the near future is plausible.

And since the last collapse was almost 12,000 years ago, maybe we're due.

Each on off event is world changing for plants and animals who live through it.

When the current collapses, temperatures drop.

And during some periods while the AMOC was off, ice sheets reached as far as New York City, Northern Spain, and Paris.

Christo's ice core study found the average temperature changed by 20 degrees Fahrenheit in the Greenland ice sheet within a few decades.

When it turned back on, it raised by nearly the same amount.

That type of temperature change in such a short period of time would be catastrophic for humanity and cause ripple effects all over the world.

- If the AMOC were to collapse, during the winter the North Atlantic would just be covered in sea ice.

So within a decade or two, all of a sudden that climate could shift from a more maritime climate that London has today to a very cold winter, continental climate that Moscow has.

- So this proves that the current is fundamentally unstable and certainly can collapse, but everything we've been talking about happened during an ice age.

What about the last interglacial when Earth was around this temperature?

Well, 128,000 years ago, the Earth was one to two degrees warmer than pre-industrial times, which is a similar temperature to today, maybe slightly warmer.

So it's a pretty good comparison to today's climate.

Remember, the cold blob that climate models say shouldn't exist?

Well, it's there today because so much ice is melting in Greenland.

That melted ice winds up in the North Atlantic and makes the ocean less salty.

And that salt is what drives the northern leg of the AMOC.

Lighter, fresher water doesn't sink, it floats, blocking the overturning current and cooling the surface temperature.

So researcher Mohamed Ezat decided to see if that cold blob existed during the last interglacial, because he wanted to understand the consequences.

- We found a warming hole during the last integration period, and this has very important implications for our under understanding of the sensitivity of the system.

- He analyzed marine sediment from the ocean floor to understand the salinity and temperature of the Northern Atlantic during the last interglacial.

- We found significant cooling associated with freshening and slowing down of the deep water formation in the Nordic Seas.

Warming climate and subsequent melting of ice could slow down the Atlantic Meridional Overturning Circulation.

- Mohamed found a slowdown or weakening of a critical part of the AMOC during the last interglacial after a blob formed.

So what does that tell us?

Well, during the last interglacial, the cold blob was bigger than ours today, but the planet was a bit warmer.

Under our current greenhouse gas trajectory, we're likely to see temperatures close to three degrees above pre-industrial times by 2100.

So if we warm a full degree Celsius above the last interglacial, we melt more ice and risk a slowing or even collapse of the current.

- The fact that the AMOC is going to be slowing down is really what we'd expect based on simple climate physics.

That's not the the question here.

It's really a question of how much is it gonna slow down and how quickly, because that's gonna determine the human impact.

- The history of this current shows how likely an AMOC slowdown or collapse really is, but there is some hope here.

The last Interglacial period, which is much more comparable to our current climate than the last Ice age, probably saw an AMOC slow down rather than a full collapse.

So whether the AMOC slows down or reaches a tipping point and collapses may very well depend on how much we warm the planet through fossil fuel emissions in the next few decades.

- The reason we're trying to keep warming below one and a half or two degrees is exactly these tipping points.

As we exceed those two degrees, the chances of hitting one of those tipping point really grows and we could hit these unexpected, catastrophic, sudden changes that we want to avoid at all costs.

- Although a weakening of the AMOC may be reversible, there would still be far reaching impacts.

It wouold get colder in Europe and the monsoons would shift.

But if we lower our warming, the AMOC could turn back on within a few decades.

However, a full collapse would leave the AMOC in its off mode for hundreds or thousands of years.

One thing's for certain, we must lower our carbon emissions to prevent negative impacts like changes in temperature, storm patterns, rainfall, and food security.

Whether we realize it or not, the AMOC and other major ocean currents have such a huge impact on how we live our lives, and to me, that's worth all the heavy debate and continued research on this topic.