Short-term geoengineering to brighten clouds over the eastern Pacific Ocean could limit the damage caused by El Niño and save the global economy trillions of dollars, although there could be winners and losers from the disruption of natural cycles.

The El Niño climate phase occurs when easterly winds weaken, allowing warm water built up in the western Pacific to slosh back across the central and eastern parts of the ocean. That heats the atmosphere and raises global temperatures, with losses to economic growth estimated in the trillions of dollars.

What could become a very strong or “super” El Niño is now developing in the eastern Pacific. But climate modelling has suggested that, in the future, a geoengineering method called marine cloud brightening might be able to cut this warming short.

The technique involves spraying tiny droplets of seawater into the air below low-lying stratocumulus clouds, where moisture condenses onto them. The clouds become whiter thanks to the increase in the number of droplets, reflecting more sunlight back to space.

Shading part of the eastern Pacific called the Niño 3.4 region via cloud brightening could interrupt the feedback loops that cause an El Niño to develop. Cooler sea surface temperatures would strengthen the trade winds to again blow warm water back into the western Pacific. More cool water would then well up from the depths of the eastern Pacific, further cooling surface temperatures, and so on.

“You can basically stop the dominoes from falling early when you do marine cloud brightening,” says at the University of California, San Diego, who worked on the study. “We’re kicking the cycle in the other direction.”

Free newsletter

Sign up to The Earth Edition

Sign up to newsletter

Wan and her colleagues got the idea from the “black summer” of catastrophic bush fires in Australia in 2019-2020, which were followed by La Niña, the opposite phase of El Niño that lowers global temperatures. Research has that drifting smoke particles brightened clouds and cooled the eastern Pacific, intensifying and prolonging the “triple dip” La Niña that began in 2020 and persisted through three winters, rather than just one or two.

The study modelled what cloud brightening could have done to the super El Niño events of 1997-1998 and 2015-2016. It found that nine months of spraying seawater would have nearly halved warming of the Niño 3.4 region, from 2°C or more to a little over 1°C. It would have ended the El Niño by January, shaving several months off the events.

The hypothetical cloud-brightening mission would have been massive, involving an estimated 2400 ships and delivering an amount of seawater spray that isn’t possible with current nozzle technology. But it would have turned a super El Niño into a moderate one.

Wan says she was surprised how well it seemed to work, given that it could only be started in June, once El Niño had clearly begun developing.

at the University of Exeter, UK, warns that these results might not translate to the real world, where warming seas typically start dissipating low-level clouds, leading to further warming and dissipation through a feedback loop.

“In a model with a stronger cloud feedback, you would have to do more aerosol injection,” he says. “The experiments seem to be at the limit of what can be done.”

Wan admits this approach could have unexpected consequences, since the model only projected the impact over two-year periods. In both simulations, La Niña started earlier after El Niño subsided, and in the 2015-2016 case, this subsequent cooler phase became stronger. That could be bad news for regions like the Horn of Africa, where strong La Niñas have, in the past, disrupted rainfall and .

But she says the idea is worth further research. Unlike geoengineering aimed at reducing global temperatures for the long term, short-term geoengineering like this could avoid the risk of “termination shock”, where any disruption to the spraying of low-level seawater or stratospheric aerosols could allow years of pent-up warming to come roaring back.

“This study is opening up doors for a completely new target for geoengineering research, which is climate variability and things like El Niño,” says Wan. “It’s potentially very powerful, because you’re not locked into these long-term risks.”

The otherworldly weirdness and beauty of fungi and slime moulds are captured in these photographs, taken by Jay Lichter for his new book , a guide to the “micro marvels” of New Zealand.

The ruby bonnet fungus (Cruentomycena viscidocruenta), pictured above, gets its scientific name from the Latin words for “bloody” and “slimy” because of the sticky substance coating its stalk, which can form large droplets. “The reflections you get in these globules from a diffused flash make for an awesome shot every time, so I never get sick of shooting them,” writes Lichter.

Below is the Cribraria slime mould, which is a protist, like certain algae and amoebas.

Below is the carnival candy slime mould (Arcyria denudata), named for the pink tufts it forms during its fruiting phase. It is only 4 to 6 millimetres tall.

Lichter discovered the relatively uncommon fungus Mycena lividorubra (below) under a log in New Zealand’s Waitākere Ranges.

And finally, below is another Mycena mushroom – though this one has been targeted by mould, “almost like a bridal veil”, Lichter writes. “But that’s not all! The mould in this photo is producing droplets of guttation (excess moisture) along its threads, making for an absolutely wild shot,” he adds.

Lichter hopes to inspire readers to discover the secret life of fungi themselves. Moss and rotten wood in the forest are your best bet, but Lichter has also found stunning specimens in car parks and vacant lots. “Even the most unassuming locations are exploding with fungal life,” he writes.

Jay Lichter
Allen & Unwin Aotearoa NZ

Tens of millions of dollars have been invested in growing seaweed to absorb carbon dioxide and slow climate change. But due to unwanted side effects, this technique could fail to significantly decrease the CO2 in the atmosphere, and it might even increase it.

Carbon dioxide removal (CDR) will be needed to meet the Paris Agreement goal of limiting global warming to 2°C, to the UN, and many have hoped seaweed could be a cheap way to do that. The US start-up Running Tide raised $70 million to grow seaweed on pucks of wood that would eventually become sodden and sink to the deep sea, sequestering the carbon, but it ran out of financing and last year.

Dutch company Kelp Blue has raised at least $2 million to expand the seaweed that it is currently growing to produce sustainable agricultural fertiliser in Namibia. Because small particles of this seaweed may break off and drift into the depths, it it could eventually “sequester and offset” up to 500 million tonnes of CO2 per year.

But a global seaweed-cultivation programme could in many places rob nutrients from phytoplankton, which also sequester carbon when they die and sink to the depths, two studies have found.

“It could backfire locally,” says at the University of Bern, Switzerland, who worked on one of the studies. “In some places, you’d actually reduce how much carbon the ocean takes up. The potential is extremely limited, with large ecological consequences.”

Except for sargassum, macroalgae species live near the coast, where nutrients are plentiful. During photosynthesis, they consume carbon dissolved in seawater, allowing the ocean to absorb more CO2 from the atmosphere.

Free newsletter

Sign up to The Earth Edition

Sign up to newsletter

Marine organisms and microbes eventually most of that seaweed, emitting an estimated nine-tenths of its carbon. To sequester more carbon, seaweed would have to be grown or transported further offshore, where it could be baled or otherwise sunk to the deep sea.

But nutrients are scarce in the open ocean, and most research before now hasn’t examined how the lack of iron could limit seaweed growth. Berger and her colleagues modelled the cultivation of 20 billion tonnes of seaweed per year across waters up to 200 nautical miles from coastlines.

They found the seaweed would quickly start depleting nitrogen, phosphorus and iron in the water, and after 25 years, its growth would have declined 95 per cent. Moreover, this would diminish global phytoplankton growth by as much as 8 per cent.

In some scenarios, seaweed cultivation could still remove billions of tonnes of CO2. But depending on what species of seaweed are grown and how much nutrients they consume, it could also increase the amount of carbon in the atmosphere by half a tonne for every tonne of seaweed carbon grown.

Patches off Senegal and southern Australia, about 0.05 per cent of the ocean, are the only places seaweed could flourish without significantly decreasing phytoplankton, the model suggests.

“If you have only a few very specific locations, you can’t grow enough seaweed to have a gigatonne of removal,” says Berger.

In another study, at the UK National Oceanography Centre and his colleagues modelled what would happen if seaweed-cultivation areas were fertilised with iron, finding that up to 40 billion tonnes of CO2 could be removed each year. But that would also halve the plankton in the ocean, with dire consequences for the fish that eat them.

“You’re robbing the surface ocean of nutrients… and transferring those to depth,” says Yool. “Essentially, you’re curtailing or slowly strangling the natural ecosystem.”

Furthermore, such seaweed cultivation and sinking would require setting up cages or other frameworks across 14 per cent of the ocean surface, largely in the nutrient-rich but stormy seas of the Southern Ocean and northern Pacific and Atlantic.

And if all this ocean wasn’t fertilised with iron, the seaweed carbon removal wouldn’t fully compensate for the plankton loss, increasing CO2 in the atmosphere by up to 700 million tonnes per year.

“You can’t just grow macroalgae and assume that you’re going to be undertaking CDR if you’re not accounting for offsetting phytoplankton growth,” says at the UK National Oceanography Centre, another member of the team.