A catastrophic climate event is upon us

Illustration by Ben Jennings

From The Guardian

The poor and middle pay taxes, the rich pay accountants, the very rich pay lawyers – and the ultra-rich pay politicians. It’s not an original remark, but it bears repeating until everyone has heard it. The more money billionaires accumulate, the greater their control of the political system – which means they pay less tax, which means they accumulate more, which means their control intensifies.

They reshape the world to suit their demands. One of the symptoms of the pathology known as “billionaire brain” is an inability to see beyond their own short-term gain. They would sack the planet for a few more stones on the pointless mountain of wealth. And we can see it happening. Last week delivered the biggest news of the year so far, perhaps the biggest news of the century. But partly because billionaires own most of the media, most people never heard it. We might find ourselves committed to a civilisation-ending event before we even learn that such a thing is possible.

The news is that the state of a crucial oceanic circulation system has been reassessed by scientists. Some now believe that, as a result of climate breakdown changing the temperature and salinity of seawater, it is more likely than not to collapse. This system – known as the Atlantic meridional overturning circulation (Amoc) – delivers heat from the tropics to the North Atlantic. Recent research suggests that if it shuts down, it could cause both a massive drop in average winter temperatures in northern Europe and drastic changes in the Amazon’s water cycles. This could help tip the rainforest into cascading collapse and trigger further disaster.

Amoc’s shutdown is likely also to cause an acceleration of sea level rise on the east coast of the US, threatening cities. It could also raise Antarctic temperatures by roughly 6C (43F) and release a vast pulse of carbon currently stored in the Southern Ocean, accelerating climate catastrophe.

Even when the countervailing effects of generalised global heating are taken into account, a further paper proposes, the net impact in northern Europe would be periods of extreme cold – including events in which temperatures in London fall to -19C, in Edinburgh to -30C and in Oslo to -48C. Sea ice in February would extend as far as Lincolnshire. Our climate would change drastically, with the likelihood of far greater extremes, such as massive winter storms. Rain-fed arable agriculture would become impossible almost everywhere in the UK.

This shift, on any realistic human scale, would be irreversible. Its speed is likely to outrun our ability to adapt. Amoc shutdowns, driven by natural climate variability, have happened before. But not in the era of large-scale human civilisation.

The first paper proposing that Amoc might have an on-state and an off-state was published in 1961. Since then, many studies have confirmed the finding and explored potential triggers and likely implications. Until recently, Amoc collapse caused by human activity fell into the category of a “high impact, low probability” event, devastating if it happens, but unlikely to occur. Research over the past few years prompted a reassessment: it began to look more like a “high impact, high probability” event. Now, in response to last week’s paper, Prof Stefan Rahmstorf – perhaps the world’s leading authority on the subject – says the chances of a shutdown look like “more than 50%”. We could pass the tipping point, he says, “in the middle of this century”.

So why is this not all over the news? Why is it not the top priority for the governments that claim to protect us from harm? Well, in large part because oligarchic power has championed a model of climate impact that bears little relation to reality: that is, they have a hypothesis about how the world works that is completely detached from scientific findings. This model underpins official responses to the climate crisis.

It began with the work of the economist William Nordhaus, who sought to assess the economic effects of global heating. His modelling suggests that a “socially optimal” level of heating is between 3.5C and 4C. Most climate scientists see a temperature rise of this kind as catastrophic. Even 6C of heating, Nordhaus suggests, would cause a loss of just 8.5% of GDP. Climate science suggests it would look more like curtains for civilisation.

As the eminent economists Nicholas Stern, Joseph Stiglitz and Charlotte Taylor have argued, the mild effects Nordhaus forecasts are merely artefacts of the model he has used. For example, his modelling assumes that catastrophic risks do not exist and that climate impacts rise linearly with temperature. There is no climate model that proposes such a trend. Instead, climate science forecasts nonlinear impacts and greatly escalating risk. The likely impacts of high levels of heating include the inundation of major cities, the closure of the human climate niche (the conditions that sustain human life) across large parts of the globe, the collapse of the global food system and cascading regime shifts – that is, abrupt transitions in ecosystems – releasing natural carbon stores, potentially leading to a “hothouse Earth” in which very few survive. Never mind a few points off GDP: there would be no means of measurement and scarcely an economy to measure.

Bizarrely, the modelling also applies discount rates to future people: their lives, it assumes, are worth less than ours. In other words, it has taken a method used to calculate returns to capital and applied it to human beings. As the three economists point out, “it is very difficult to find a justification for this in moral philosophy.” Moreover, climate impacts disproportionately affect the poor – but under the models, their lives are also priced down.

Unsurprisingly, models of this kind, Stern, Stiglitz and Taylor note, have been seized on by “special interests” such as the fossil fuel industry to argue for minimal responses to the climate crisis. And it’s not just the oil companies. Bill Gates, who claims to want to protect the living planet, has given $3.5m (£2.6m) to a junktank run by Bjorn Lomborg, who has built his career on promoting Nordhaus’s model, thus helping to downplay the need for climate action. Nordhaus was awarded the Nobel Memorial prize for economics for his pernicious nonsense – and it is deeply embedded in government decision-making.

A billionaire death cult has its fingers around humanity’s throat. It both causes and downplays our existential crisis. The oligarchs are not just a class enemy but, as they have always been, a societal enemy: a few thousand people can destroy civilisations. It’s the billions v the billionaires, and the stakes could not possibly be higher.

Is the Gulf Stream approaching a tipping point?

 From Oceanography

It's a long article, so I'll just share the conclusions with you here.  But I urge you to read the whole piece, so you can understand just how very serious this is.  The article is by the famous climate scientist Stefan Rahmstorf.  AMOC = Atlantic Meridional Overturning Circulation, of which the Gulf Stream is a part.

The current cold blob is already affecting our weather, though not in the way that might be expected: a cold subpolar North Atlantic correlates with summer heat in Europe (Duchez et al., 2016). The cooling of the sea surface is enough to influence the air pressure distribution in a way that encourages an influx of warm air from the south into Europe. For example, in summer 2015, the subpolar Atlantic was the coldest since records began in the nineteenth century—​while Europe suffered a strong heatwave. Subsequent study has shown that heatwaves are increasing three to four times faster in Europe than in other regions of the Northern Hemisphere, related to changes in the jet stream that may well be influenced by the cold blob (Rousi et al., 2022).

Several studies show that if the AMOC weakens, sea levels on the American northeast coastline will rise more sharply (e.g., Levermann et al., 2005; Yin et al., 2010). The Coriolis force pushes moving water, in this case, in the Gulf Stream, to the right, away from the American coast. When the Gulf Stream weakens, less water is moved northward, causing water levels to rise inshore of the Gulf Stream, with models projecting a 15–20 cm rise by 2100 from this effect alone, in addition to other causes of rising seas. Coastal erosion, the frequency of nuisance flooding, and extent of storm surge damage will substantially increase.

A collapse of convection in the subpolar gyre would significantly magnify these problems. Figure 14 shows the expected temperature change in this case. It is not so much the absolute change, but the changes in temperature contrast between neighboring regions—here, the cold ocean relative to the adjacent warm land masses—that will greatly change the dynamics of the weather, as temperature gradients drive weather activity in ways we can’t foresee in detail. Even this limited oceanic change will shift tropical rainfall belts, though not by as much as a full AMOC shutdown.

FIGURE 14. Temperature changes in the model-mean before and after a collapse of convection in the subpolar gyre region are plotted here. From Swingedouw et al. (2021).

A full shutdown of the AMOC would have truly devastating consequences for humanity and many marine and land ecosystems. Figure 15 shows the model of Liu et al. (2017) after a doubling of CO2, with an AMOC collapse caused by this CO2 increase. The cold air temperatures then expand to cover Iceland, Britain, and Scandinavia. The temperature contrast between northern and southern Europe increases by a massive 4°C, likely with major impact on weather, such as unprecedented storms.

FIGURE 15. Annual-mean near-surface air temperature change resulting from a CO2 doubling and AMOC breakdown. While Earth is much warmer, the northern Atlantic region has become colder. In winter, the cooling there is much larger still. From Liu et al. (2017). 

Figure 16 shows the precipitation changes in this model. As we have seen in the paleoclimate data for Heinrich events, major precipitation shifts in the tropics would likely cause drought problems in the northern tropics of America as well as Asia. Seasonal changes will be even larger than these annual mean changes. Other simulations predict a significant increase in winter storms in Europe and a “strong reduction of crop yield and pasture” there (Jackson et al., 2015).

FIGURE 16. Annual-mean precipitation change resulting from a CO2 doubling and AMOC breakdown. Most concerning is the southward shift in tropical rainfall belts and a generally drier Europe. From Liu et al. (2017).

The IPCC summarized the impacts: “If an AMOC collapse were to occur, it would very likely cause abrupt shifts in the regional weather patterns and water cycle, such as a southward shift in the tropical rain belt, and could result in weakening of the African and Asian monsoons, strengthening of Southern Hemisphere monsoons, and drying in Europe” (IPCC, 2021, TS p. 73). Some further consequences include major additional sea level rise especially along the American Atlantic coast, reduced ocean carbon dioxide uptake, greatly reduced oxygen supply to the deep ocean, and likely ecosystem collapse in the northern Atlantic.

The risk of a critical AMOC transition is real and very serious, even if we cannot confidently predict when and whether this will happen. We have already left behind the stable Holocene climate in which humanity has thrived (Osman et al., 2021), and the latest IPCC report warns us that beyond 1.5°C of global warming, we move into the realm of “high risk” with respect to climate tipping points (IPCC, 2023).

Also at risk is the Southern Hemisphere equivalent of the northern Atlantic deep-water formation: the Antarctic bottom-​water formation. A recent study by Australian researchers concluded that the increasing meltwater inflow around Antarctica is set to dramatically slow down the Antarctic overturning circulation, with a potential collapse this century (Q. Li et al., 2023). That will slow the rate at which the ocean takes up CO2 (hence, more will accumulate in the atmosphere), and it will reduce the oxygen supply for the deep sea.

A full AMOC collapse would be a massive, planetary-scale disaster. We really want to prevent this from happening.

In other words: we are talking about risk analysis and disaster prevention. This is not about being 100% or even just 50% sure that the AMOC will pass its tipping point this century; the issue is that we’d like to be 100% sure that it won’t. That the IPCC only has “medium confidence” that it will not happen this century is anything but reassuring, and the studies discussed here, which came after the 2021 IPCC report, point to a much larger risk than previously thought.

The Global Tipping Points Report 2023 was published in December 2023, a 500-page effort by 200 researchers from 90 organizations in 26 countries (Lenton et al., 2023). Its summary conclusion reads: “Harmful tipping points in the natural world pose some of the gravest threats faced by humanity. Their triggering will severely damage our planet’s life-support systems and threaten the stability of our societies.”

For the AMOC and other climate tipping points, the only action we can take to minimize the risk is to phase out fossil fuel use and stop deforestation as fast as possible. If we can reach zero emissions, further global warming will stop within years, and the sooner this happens the smaller the risk of passing devastating tipping points. It would also minimize many other losses, damages, and human suffering from “regular” global warming impacts (e.g., heatwaves, floods, droughts, harvest failures, wildfires, sea level rise), which are already happening all around us even without the passing of major climate tipping points.

As another Climate Tipping Points report published in December 2022 by the Organisation for Economic Co-operation and Development (OECD) concludes: “Yet, the current scientific evidence unequivocally supports unprecedented, urgent and ambitious climate action to tackle the risks of climate system tipping points” (OECD, 2022).

It would be irresponsible, even foolhardy, if policymakers, business leaders, and indeed the voting public continue to ignore those risks.

Rahmstorf has written a piece that someone who is not a climate scientists can easily understand.    It couldn't be clearer.  We have to cut our emissions as fast as possible.  And we are not.

Irreversible change to the Gulf Stream

 From NBC News

The Atlantic Ocean’s current system, an engine of the Northern Hemsiphere’s climate, could be weakening to such an extent that it could soon bring big changes to the world’s weather, a scientific study said on Thursday.

The Atlantic Meridional Overturning Circulation (AMOC) is a large system of ocean currents that transports warm water from the tropics northwards into the North Atlantic.

As the atmosphere warms due to increased greenhouse gas emissions, the surface ocean beneath retains more of heat. A potential collapse of the system could have severe consequences for the world’s weather systems.

Climate models have shown that the AMOC is at its weakest in more than a 1,000 years. However, it has not been known whether the weakening is due to a change in circulation or it is to do with the loss of stability.

The study, published in the journal Nature Climate Change, said the difference is crucial.

“The loss of dynamical stability would imply that the AMOC has approached its critical threshold, beyond which a substantial and in practice likely irreversible transition to the weak mode could occur,” said Niklas Boers at the Potstdam Insitute for Climate Impact Research and author of the study.

By analyzing the sea-surface temperature and salinity patterns of the Atlantic Ocean, the study said the weakening of the last century is likely to be associated with a loss of stability.

“The findings support the assessment that the AMOC decline is not just a fluctuation or a linear response to increasing temperatures but likely means the approaching of a critical threshold beyond which the circulation system could collapse,” Boers said.

If the AMOC collapsed, it would increase cooling of the Northern Hemisphere, sea level rise in the Atlantic, an overall fall in precipitation over Europe and North America and a shift in monsoons in South America and Afrcia, Britain’s Met Office said.

Other climate models have said the AMOC will weaken over the coming century but that a collapse before 2100 is unlikely.

Here's the abstract for the Nature Climate Change article:

The Atlantic Meridional Overturning Circulation (AMOC), a major ocean current system transporting warm surface waters toward the northern Atlantic, has been suggested to exhibit two distinct modes of operation. A collapse from the currently attained strong to the weak mode would have severe impacts on the global climate system and further multi-stable Earth system components. Observations and recently suggested fingerprints of AMOC variability indicate a gradual weakening during the last decades, but estimates of the critical transition point remain uncertain. Here, a robust and general early-warning indicator for forthcoming critical transitions is introduced. Significant early-warning signals are found in eight independent AMOC indices, based on observational sea-surface temperature and salinity data from across the Atlantic Ocean basin. These results reveal spatially consistent empirical evidence that, in the course of the last century, the AMOC may have evolved from relatively stable conditions to a point close to a critical transition.

Here's an article about AMOC  from Carbon Brief, which is also the source of the chart.

Schematic of the AMOC. The red pathways show warmer water nearer the surface, while the purple pathways show colder, more dense water moving at depth. Credit: Met Office

We are clearly in a climate emergency.  We need to move fast to cut emissions.  And we are still dithering.

The 8.2 ka event

A most interesting blog post from RockyRex, about an anomalous episode during the warm up from the last ice age, when, for a period lasting just 150 years, global temperatures plummeted before resuming their up trend.  Scientists now think that this was due to the catastrophic failure of an ice dam which had been keeping a very large body of meltwater behind it.  When this fresh water flooded into the sea, it affected the thermohaline circulation of sea water.  Fresh water is less dense than salt water, so it remained on the surface of the sea, displacing the gulf stream further south and weakening it.  Northern hemisphere temperatures dropped 2 C in a couple of decades, and the sea level rose by between 0.4 and 2.1 metres.

The current rapid melting of Greenland's ice cap appears to be producing a similar "cold blob" in the Atlantic, and the Gulf Stream has slowed.  If this process gains strength--very likely as Greenland's melt accelerates--there will be a temporary (100 years plus?) cooling of the North Atlantic.  No doubt the denialists will say, see, we told you so, the world is cooling.  What seems to be certain though, is that this "cold blob" combined with much warmer seas around it, is responsible for the record floods in Scotland and Northern England over the last few years.

Read more of RockyRex's post here.