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A crew works in March on collector containers, where air is collected, at the Climeworks carbon-capture plant in Hellisheidi, Iceland.FRANCESCA JONES/The New York Times News Service

Gwynne Dyer is a historian, journalist and the author of Intervention Earth: Life-Saving Ideas from the World’s Climate Engineers.

Three years ago, I set out on a journey to tap into the knowledge of scientists and explore how we can counter the effects of climate change. I interviewed almost 100 climate scientists together with assorted engineers and entrepreneurs, and I learned about many new technologies in the early stages of development that will, when implemented at scale, help to mitigate climate change. The global climate emergency is real and urgent, but there is some good news.

Twenty years after wind farms and photovoltaic solar arrays began to proliferate, a cornucopia of new technologies for producing and storing non-fossil-fuel energy is spilling out onto the table. For example, the same fracking techniques used by the oil companies are now giving access to the hot rock that is available almost everywhere two or three kilometres below the surface. That means we can get limitless superheated steam to run turbines simply by pumping water through a closed system with hot rock at depth and turbines on the surface. The first megawatt-scale geothermal plant opened in Nevada late last year.

New ways are emerging to stop carbon-dioxide emissions from steel and cement-making, which together account for 15 per cent of greenhouse-gas emissions. Electric vehicles are proliferating, and technologies for the long-term storage of electricity, essential in a renewables-based system, are finally getting the attention they deserve.

The bad news comes in two parts. One is that emerging techniques like these normally take 10 to 15 years to scale up, which is not much use in holding the warming down now. The other is that more than four-fifths of the world’s energy – 82 per cent – still comes from fossil fuels. People talk a lot about cutting emissions, but it isn’t actually happening. “We’re not getting rid of fossil fuels,” U.S. President Joe Biden said in 2020. “We’re getting rid of the subsidies for fossil fuels, but we’re not getting rid of fossil fuels for a long time.”

There is a remote possibility that the human race will spontaneously transform itself and halve its emissions by 2030, but prudence demands that we also plan for the future in which that miracle doesn’t happen. Especially because the science is getting quite scary.

As scientists began to understand more about the Earth system, they realized that global warming rarely happens smoothly. It tends to happen in sudden, often irreversible lurches, when it reaches a “tipping point” – and the scientists can’t be sure where those tipping points are. They all agree, however, that the tipping points multiply once the average global temperature exceeds 1.5 C hotter than the pre-industrial temperature.

Back in 2015, the Intergovernmental Panel on Climate Change made staying below 1.5 C at least into the 2030s its “aspirational goal,” but we have just had our first full year at that temperature. We are already in the danger zone and we will probably remain there, exposed to surprise upward surges in temperature at any time, so it would be very useful to have some techniques available for holding the temperature down.

Such techniques exist in theory. They are collectively known as “geoengineering,” a set of proposed technologies for manipulating the environment that could partly offset some effects of global warming. But many people, including even some scientists, oppose testing them. “It’s dangerous nonsense,” Hans Schellnhuber, a renowned German climate scientist, told me when I was writing my first book on climate in 2008. “It would actually be a complete failure of the human enterprise, because it is supping with the devil, in my view. First of all, I’m very doubtful that the governments of the world would agree. The Chinese would have to agree, and the Russians, and we are not able to agree on even the most sensible things. So how to agree on a crazy thing? The other thing is, we do not really know what the side effects would be. The very existence of this narrative is a dangerous one.”

While it is unusual for scientists to oppose research, Dr. Schellnhuber’s views on investigating geoengineering techniques weren’t uncommon at the time. In the rush of naive enthusiasm after the first international treaty on climate change was signed in 1994, almost everybody assumed that the problem could and would be solved by cutting emissions alone.

To suggest that other measures might also be needed came to be seen as defeatist, almost treasonous. Some prominent climate scientists were militantly opposed to research on geoengineering even as an emergency measure, and most others just kept their heads down.

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It’s true that mitigation (cutting emissions) really is the only way to stop the warming permanently, as every advocate of geoengineering research acknowledges. However, if the average global temperature goes too high (say, 2 C higher than pre-industrial levels, the current agreed-upon “never-exceed” target), then things start to fall apart.

The death toll rises, food production plummets, governments collapse, wars and mass migrations become the norm. The great fear is that, in the ensuing chaos, mitigation is simply abandoned.

But so far, the emissions cuts the world agreed to enact haven’t happened: The politics is much harder to do than the scientists imagined. Pro-geoengineering scientists talk about “peak-shaving”: holding the temperature down long enough for real reductions in emissions to kick in, and staving off collapse in the meantime. However, the taboo on geoengineering lingers to this day, and it has left us with no ready defence against rapid or even runaway warming.

We have to recognize that we are now in the driving seat, we are the dominant force on planet Earth,” Johan Rockström, the director of Germany’s Potsdam Centre for Climate Impact Research, told me in 2022. (Like many climate scientists, he recognized the need for geoengineering but couldn’t quite bring himself to say the word.)The global human enterprise exceeds any volcanic eruption, any earthquake, even solar radiative changes. We are simply so big and so dominant that we now need to drive the vehicle. Currently we are just sitting there and not really recognizing that we are the ones with the levers now. We are starting to understand how these levers work, but we are not using them, and it’s time to use them.”

The techniques for holding the temperature down are known in theory, and are neither dangerous nor very expensive. The two most promising ones are stratospheric aerosol injection and marine cloud brightening.

Stratospheric aerosol injection would put sulphur dioxide in the stratosphere, just as big volcanoes do when they explode. The Earth is cooled, no living things are harmed, and at worst the ozone hole over the Antarctic heals a bit more slowly.

Marine cloud brightening sprays trillions of tiny droplets of seawater over the ocean surface from unmanned, satellite-directed vessels. Convection carries some of the droplets up into low-lying clouds and thickens them so they reflect more sunshine. Lots of cooling, no harm done.

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The first small open-air experiments with marine cloud brightening got under way under the auspices of Southern Cross University in Australia in 2020, and a team from the University of Washington began doing similar tests this spring in California despite an outcry from the usual suspects, but the de facto ban on even the tiniest open-air tests of stratospheric aerosol injection remains absolute.

The Swedish government authorized an extremely small-scale test of how sulphur dioxide gas might be dispersed in the atmosphere (using a different, quite harmless gas) in 2021, but withdrew its permission when the anti-geoengineering lobby mobilized.

It would take years to get either technique up and running at scale, so we’d be in real trouble if we hit an early tipping point and the average global temperature jumped. We may be in just that kind of trouble, because the past year was likely the hottest in the past 100,000 years. The average global temperature is now fully 0.2 C hotter than the same time last year. The 50-year trend in global warming was 0.18 C per decade, as confirmed by a study in Nature in 2022; this is more than 10 times as fast.

Climate scientists’ predictions are normally very accurate, and nobody knows why they are so far out this time. It’s possible that we have hit an early tipping point: “If the anomaly does not stabilize by August, then the world will be in uncharted territory,” says Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies.

But at least more and more climate scientists are getting over their skittishness about geoengineering. I recently followed up with Dr. Schellnhuber, who is now director-general of the International Institute for Applied Systems Analysis in Austria. He replied: “I think in the end, if you really put me on the spot, and I would have to decide whether yes or no, and we have exhausted all other possibilities, and this would be a fair chance to avoid a hothouse Earth … then I would probably say grudgingly, ‘Yes. Let’s do it.’ ”

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