The ocean acts like a giant air-conditioner, absorbing 90% of extra heat added by humans. What if it stops? Dr. Keith Moore explains. From New Zealand, Dr. Kevin Trenberth reports more record ocean heating – levels not seen for over a million years. Is this powering weather extremes?

Download or listen to this Radio Ecoshock show in CD Quality (57 MB) or Lo-Fi (14 MB)



I just heard the prominent Australian climate scientist Dr. Will Steffen has passed at age 76. Steffen advised the Australian government and lead many groups tracking climate threats to Australia and possible solutions. But he was much larger than Australia. For a few years Steffen led the Stockholm Resilience Centre – a very influential group that produced the concept of Planetary Boundaries, among others.

In fact, Steffen’s insights and gifts are so large I will have more about Will’s key ideas in next week’s Radio Ecoshock show, including excerpts from my two interviews with him. Steffen advanced fundamental concepts which shape our understanding of the future. Tune in for that next week.

Fellow Australian David Spratt has a full and fitting tribute to Will Steffen, just published at the Climate Code Red blog. The title is: “Will Steffen’s crucial climate ideas on ‘Hothouse Earth’, tipping cascades and non-linearity.”




Dr. Kevin Trenberth is a Distinguished Scholar at NCAR – the U.S. National Center for Atmospheric Research. He also works with the University of Auckland. Kevin was a lead author of the 2001 and 2007 IPCC Scientific Assessment of Climate Change.

Kevin is co-author of another new paper with an amazing team of scientists. This Open Access paper is titled “Another Year of Record Heat for the Oceans”. Once again, like last year’s new record for global marine heat, these hotter seas come despite three years of the La Nina condition, which works to cool the sea. Extra heat caused by human greenhouse gases have overcome even the strongest cooling system in the ocean. Just imagine when the ocean releases it’s own heat instead, in the El Nino state, which is expected to start developing this summer (maybe). That is partly why a number of scientists have warned 2024 could be hotter than any time humans have seen before.

Listen to or download my 26 minute interview with Kevin Trenberth in CD Quality or Lo-Fi



There are many worrying ramifications. One example: when hurricanes or tropical cyclones develop, they pull up energy from the sea. But if they get strong enough, they begin to churn up somewhat cooler waters below the surface, moderating their energy. Now, as scientists have clearly measured, the oceans are getting hotter further below the surface. So that colder water braking is no longer available. We should expect even more powerful big storms to hit land, due to heat going deeper. Those storms will also carry more extreme rains because a warmer atmosphere hold more water vapor – and because more water evaporates when sea surface temperatures are hotter.


The ocean circulates waters through “the Great Conveyor Belt” – a system of currents that flow near the surface in the North Atlantic, before diving deep in the Arctic – and then returning through the deep all the way to Antarctica. Several scientific guests on Radio Ecoshock report the Atlantic Meridional Overturning Circulation (AMOC) is already weakening. If that weakening continues, Eastern North America, the UK, and Scandinavia could have noticeably colder weather.

One driver of the changes depends on the amount of salt carried in sea water. Saltier water is heavier and so tends to sink to the bottom, keeping the circulation going. But a-historic heat in the Arctic is melting so much ice that fresher water is changing the circulation.

There is a counter-part for the Atlantic Current called the Southern Meridional Overturning Circulation (SMOC). Our second guest, Dr. Keith Moore University from California at Irvine, just published a study in Nature suggesting at some point of warming, the Southern Meridional Overturning Circulation could stop. Marine life, including the base of the food chain, could crash.


What do heating oceans do? Hotter oceans capture less carbon dioxide from the atmosphere. They also hold less oxygen, which can diminish sea life, including food fisheries. Ocean take a long time to heat, and a long time to release that heat again. Our greenhouse gas heating is guaranteeing a hotter future for all our descendants for centuries, likely millennia. In previous Radio Ecoshock interview, Trenberth told us about the killing effect of marine heat waves on coral, fish, all kinds of species.

You can find out more on this new science with this excellent Guardian article by Damain Carrington, published January 11, 2023.

Canadian climate scientist Paul Beckwith covers both the Guardian article and new ocean heat science in this YouTube video posted January 20.




Also mentioned in my interview with Kevin Trenberth: “Drivers and distribution of global ocean heat uptake over the last half century”, author Maurice F. Huguenin, published September 7, 2022 in Nature Communications (Open Access, free). Another is “Past and future ocean warming”, October 18, 2022 in Nature (abstract only, behind a paywall). You can read about that in this Washington Post article (if you have a subscription).

I have posted all my previous interviews with Kevin Trenberth at the bottom of this blog. These are fairly recent and you can’t go wrong learning from Dr. Trenberth. He is one of the best, and yet able to explain things clearly for all of us.




Now we look into the way atmosphere and oceans interact in the home of ocean life. Tiny sea life, the Plankton, capture excess carbon dioxide from the atmosphere. They release most of the oxygen we breath. Plankton could face famine if major ocean currents change, especially in the Southern Ocean. Our whole game of existence is on the line in cold deep waters where no humans go.

I am not easily scared by science. But the work of our guest Keith Moore and his colleagues paints a possibility of outright extinction-level catastrophe for ocean life and all life – if we continue heating the planet. I don’t know how we all missed this.

Keith Moore is Associate Professor of Earth System Science at the University of California Irvine. After his Doctorate in Oceanography, Moore specialized in a new field called Ocean Biogeochemistry. In 2018, Moore led a foundational study called “Sustained climate warming drives declining marine biological productivity.” Now he is back as co-author of “Reduced CO2 uptake and growing nutrient sequestration from slowing overturning circulation”. Does that sound boring? How about a quadrupling of CO2 in the atmosphere by 2250, a possible shortage of oxygen to breath, and a mass die-off of sea life including food fisheries – all lasting a thousand years or more. Does that sound important?

Listen to or download my 24 minute interview with Keith Moore in CD Quality or Lo-Fi


Many of our climate hawks know about the ocean system called the Atlantic Meridional Overturning Circulation or AMOC. People in North America call it the Gulf Stream. It warms Eastern North America, the UK and Europe. A number of recent studies show the flow of these waters is weakening. But in this interview we learn more about AMOC’S Southern counterpart: SMOC, the Southern Meridional Overturning Circulation.

The Decade After Tomorrow


It is not easy to grasp what SMOC is. Even the Wikipedia page about it warns “This article may be too technical for most readers to understand.” I looked at a half dozen graphics before getting the idea. My impression begins with the legendary high winds in the Southern Ocean. Sailors call them “The Roaring Forties” and it’s damn dangerous for ships of any kind. Very strong Westerly winds blow between 40 Degrees Latitude South (getting close to Antarctica) and 50 Degrees S. (at the southern tip of South America). There is no land, no mountain, to slow those winds down.

The winds churn up the ocean into giant waves. That causes a lot of mixing from the surface down into deeper layers. By the way, over the last few decades those winds have been tightening toward the south, toward Antarctica, which changes weather in Australia and New Zealand.

The undersea motion and exchanges get harder to understand closer to Antarctica. The winds are a big factor, but so is melting glacier water (being lighter, that stays near the surface). SMOC describes two operations or “cells”, and each of those have upwelling and downwelling. I’m still trying to figure it all out.

Here is what Keith Moore said in a University of California Irvine Press Release:

Green, downward lines denote dead and dying organisms sinking from surface waters in the world’s oceans. As they decompose, the animals’ nutrients are released at depth, eventually to return to the surface via ocean circulation. A recently published Nature Climate Change study by UCI Earth system scientists shows how global warming will slow deep circulation, trapping nutrients near the ocean floor. Marine ecosystems will become increasingly nutrient-starved over time. Slowing deep circulation also reduces uptake of carbon dioxide from the atmosphere, resulting in the extension and intensification of hot climate conditions.

A disruption in circulation would reduce ocean uptake of carbon dioxide from the atmosphere, intensifying and extending the hot climate conditions. Over time the nutrients that support marine ecosystems would increasingly become trapped in the deep ocean, leading to declining global-ocean biological productivity.

Key for Keith Moore’s interview are two factors: (a) the southern overturning returns nutrients that feed fisheries in the Caribbean and North Atlantic and (b) in the right climate conditions, SMOC can rather suddenly stop. That has happened before in prehistoric ages. You can imagine the starving ocean life, and humans on land if that key southern ocean circulation ended.

But even if the Southern Meridional Overturning weakens, fewer nutrients will be available for the basis of marine life: plankton. Remember, “plankton” is not just one species. The word just means tiny, often microscopic, living things in the ocean. Some plankton are plants (the famous photosynthisizers), while other plankton are tiny animals (sometimes the juvenile form of ocean creatures we know).


If plankton is in trouble because there is less food, marine photosynthesis will decline. That means (a) less oxygen will be available to organisms in the sea, and on land and (b) less carbon dioxide will be sucked up by marine organisms. The ability of phytoplankton to capture carbon dioxide from the air (via the surface ocean) is one reason Earth has not heated as much as expected. As you heard, the ocean absorbs up to 25% of the excess carbon dioxide humans emit. If that percentage drops with the plankton, then land and atmosphere will reflect the true value of our greenhouse gases. With new science, as Keith Moore tells us, this carbon reality check is a developing possibility, especially if we stay on our current high-emission path.

In 2016, we had Russian plankton expert Sergei Petrovskii on Radio Ecoshock. His paper said the future of plankton under global warming is unknown. That echoes a 2015 paper by Laufkötter and Gruber. But now, with this new understanding of how the great ocean circulation delivers nutrients between the hemisphere, Moore and others are confident global warming is bad for plankton and will lead to a decrease in ocean productivity. Taken to the worst outcome, I presume that could lead to mass extinction in the sea. But we may not push it that far…


More Stifle Than Drown



You should also check out this 2018 paper, led by guest Keith Moore: “Sustained climate warming drives declining marine biological productivity.

They find: “Potential fishery yields, constrained by lower–trophic-level productivity, decrease by more than 20% globally and by nearly 60% in the North Atlantic. Continued high levels of greenhouse gas emissions could suppress marine biological productivity for a millennium.

And check out this accompanying Science Perspective by Laufkotter and Gruber: “Will marine productivity wane?

I have more on the mind-blowing implications of Moore’s science below. And you can get an introduction to the paper in this Press Release from University of California Irvine.




Most of humanity live in the Northern Hemisphere. If you follow climate at all, you hear about the Atlantic Meridional Overturning Circulation or AMOC, or at least it’s component the Gulf Stream. Several scientists appeared on Radio Ecoshock reporting both measurements and models suggest the Atlantic AMOC current is already slowing down. If that continues, winters in both Eastern North America and especially the UK and North Europe would be colder, as their true latitude suggests. That is a regional effect.

In 2017, a paper was published in Science Advances called “Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate.” The authors say:

By correcting the model biases, we show that the AMOC collapses 300 years after the atmospheric CO2 concentration is abruptly doubled from the 1990 level.

According to a new paper, still under review, by famous NASA scientist James Hansen, when we account for all warming gases, not just carbon dioxide, the atmosphere has already reached doubling over pre-industrial. So we wonder: are we already committed to possibly collapsing the Gulf Stream, the whole AMOC ocean system, around the year 2300? Have we changed long history, sending Northern Europe back into a “Little Ice Age” scenario in a couple of hundred years?

But as Kevin Trenberth told us, the Southern Ocean is much larger than the Atlantic. The Southern Ocean is uninterrupted by land in places, wrapping around the globe. If most extra heat from the Greenhouse Effect has been absorbed by the ocean, the larger part of that goes into the Southern Ocean.

That happens partly because of a massive mixing machine around Antarctica. Heated surface waters are thrown down to the bottom. It will take hundreds if not thousands of years for that warmed water to return to the surface where it can affect the atmosphere. The mixing that has limited climate damage so far is dependent on two things:  whether winds get even stronger in the Southern Ocean, churning up the seas, capturing carbon and oxygen – or weaker as the world warms. Related to that, but also operated by a pump of salinity – i.e. salt-loaded dense water sinks below fresh – is SMOC, the Southern Meridional Overturning Circulation.

We heard science from several quarters suggesting the Northern overturning is weakening. Now we have science to show the Southern overturning could not only weaken, but could stop operating. Investigations show that has happened before in past ages. We are still working to define what the trigger for the demise of SMOC is. Our guest suggests that trigger might live within the upper range of heating still possible if humans continue to load up the atmosphere at our present rate.

A 2010 study by John Marshall and Kevin Speer said:

It is now thought that Southern Ocean upwelling has an importance that rivals the Atlantic downwelling branch for our understanding of climate and climate variability, because it controls the rate at which the ocean reservoirs of heat and carbon communicate with the surface.”

The possible impacts are staggering, almost beyond imagination

Scientists agree the global ocean has been absorbing 90% of our added heat. If the Southern overturning collapses, we may experience double the heating, ton for ton of carbon we add to the sky. Regional climates, and so weather, would change all over the world. The hydrological cycle would change, creating winners and losers for droughts, rain, and floods. There would be fewer nutrients flowing toward feeding layers in the tropics and Northern Hemisphere. Fisheries might collapse as plankton declines. In such a massive instability, wide-spread extinctions sound likely to me.

A 2018 paper in Science, led by our guest Keith Moore, found:

Projected increases in greenhouse gas emissions could suppress marine biological productivity for a thousand years or more… This decrease will result from a global-scale redistribution of nutrients, with a net transfer to the deep ocean. By 2300, this could drive declines in fisheries yields by more than 20% globally and by nearly 60% in the North Atlantic.

But if plankton declines, so does the oxygen you and I need to breathe.

In 2016, the Russian-trained plankton expert Sergei Petrovksii told Ecoshock listeners the future of plankton in a warming world was very uncertain. But whether plankton thrived or decreased, his models showed a severe crash in plankton by about 2070. In his paper, Petrovskii said: quote:

It is estimated that about 70% of the Earth atmospheric oxygen is produced by the ocean phytoplankton. Correspondingly, one can expect that a decrease in the rate of the oxygen production by phytoplankton may have catastrophic consequences for life on Earth, possibly resulting in mass extinction of animal species, including the mankind. Therefore, identification of potential threats to the oxygen production is literally an issue of vital importance.

One more thing: in his 2018 paper, Keith Moore found carbon dioxide levels in the atmosphere would skyrocket if a famine of nutrients causes plankton die-off. Current CO2 levels are around 419 parts per million. You are living through the extreme climate that causes. But the Moore group study, based on business-as-usual high emissions, takes carbon dioxide in the atmosphere to about 1960 parts per million in a couple of hundred years. That is more than quadruple.

We recall a paper and Ecoshock interview with Professor Tapio Schneider from the California Institute of Technology and NASA. They found low clouds around the tropics would not be able to form somewhere around 1200 parts per million. This essential cooling cover could be lost well before we get to 1960 ppm. So modeling by Moore and colleagues blast us way past that danger line…Earth could become over 10 degrees C. hotter on average. Human beings and most life as we know it would be gone – by 2250! Scientists now worry that is possible.

The great collapse in ocean circulation has not happened yet. It is not pre-ordained. But those are the towering risks we take with our fun holiday flights, the whole consume and throw-away economy – while postponing a rush to renewables. We are playing Russian Roulette with the ocean. Will we stop before the seas stop moving? Young people: look to the ocean. Your future is out there in the deep sea.

I’m Alex Smith. Thank you for braving the awful truth – and still caring about this world.


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Weather Madness

Weather Madness
Posted on September 7, 2022

Alex covers two months of weather madness in 10 minutes. Then top scientists Kevin Trenberth and Dennis Hartmann explain La Nina, the ozone hole, and probable futures.

Listen to or download this new 22 minute interview with Dr. Kevin Trenberth in CD Quality or Lo-Fi



Hot Oceans & Escaping Consumerism – Trenberth & Harris

Hot Oceans & Escaping Consumerism – Trenberth & Harris

Posted on January 26, 2022

The oceans just keep getting hotter, even during this La Nina year, despite the pandemic. Dr. Kevin Trenberth, Distinguished Scholar at the U.S. National Center for Atmospheric Research.

Listen to/download this 24 minute Radio Ecoshock interview with Kevin Trenberth in CD Quality or Lo-Fi



When the Weird Becomes Harder

When the Weird Becomes Harder

Posted on September 30, 2020

Even during the pandemic, 2020 offers more wildfires, strong storms, heat waves, low sea ice and melting glaciers. NCAR Distinguished Scholar Kevin Trenberth and from the UK, Professor Mike Benton, two scientists at the top of their game, explain how we got here and where this goes. We cover it all from ice to ocean heat waves to mass extinction.





Kevin Trenberth – Ocean Heat Warning!

Feb 2, 2020
Super-scientist Kevin Trenberth on record ocean warming: impacts now and for centuries to come. From Radio Ecoshock Feb 5, 2020.


Climate Disaster: Greenland Is Melting! (NEW SHOW)

Climate Disaster: Greenland Is Melting!

Posted on September 4, 2019

Super-scientist Kevin Trenberth from the U.S. National Center for Atmospheric Research talks hot oceans, stronger hurricanes (like Dorian), and Greenland melting 2 to 3 times faster than scientists thought possible. Kevin makes a surprising announcement about his own future: this famous scientist is leaving Trump’s America, as the United States of Denial guts climate regulations.




Climate Disaster: Greenland is Melting!—Kevin Trenberth on global warming—Radio Ecoshock 2019-09-04