Falling launch costs could put a giant sunshade to cool the Earth within reach, though some call it fantasy

A report from the Planetary Sunshade Institute, a Los Angeles non-profit, estimates that a sunshade in space could cool the planet by about 1 degree Celsius and that building one might become viable in 20 to 40 years. The enabling condition is cheaper heavy-lift rockets able to haul millions of tonnes of material beyond Earth orbit. Nature’s coverage on October 28, 2026 put the idea in front of a wider audience, along with its critics.

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Chantal Cappelletti, a space-systems engineer at the University of Nottingham who belongs to the report’s consortium, told Nature that many people dismiss the concept as “just fantasy,” while falling launch costs make it look more achievable than it once did. Daniele Visioni, a Cornell University climate scientist who used to wave space-based schemes away as science fiction, now says they deserve more attention. He still does not consider the approach feasible before 2100.

Who paid for the sunshade study

The analysis, as Nature reported, was funded with a £400,000 grant, about $530,000, from the UK’s Advanced Research and Invention Agency, known as ARIA, inside a £56.8 million solar-geoengineering programme. The report summarizes work by engineers and climate scientists, some of them at space agencies such as NASA, and is described as the most detailed analysis yet of such methods. A summary of the article on News Beep adds that Morgan Goodwin, the institute’s executive director, ties the interest to an accelerating climate crisis.

ARIA’s own awards, announced in May 2025 and reported by The Chemical Engineer, were spread over 21 research teams. One team including NASA and University of Nottingham engineers received £400,000 to model six conceptual designs for space reflectors. The same programme funded Arctic sea-ice thickening, cloud brightening and aerosol balloon tests, so the sunshade work is a small slice of the programme.

The funder’s own commentary shows how cautious the framing is. Pete Irvine of the University of Chicago said the programme should not be seen as a rush to develop and deploy these technologies, while Mike Hulme of the University of Cambridge argued that they remain speculative until deployed at scale, so small studies cannot show they are safe, effective or reversible. ARIA chair Matt Clifford described the work as carefully controlled research that embodies the agency’s mission.

A roadmap that ends in 2080

The engineering case rests on a paper published in April 2026 by Catello Leonardo Matonti, Marina Coco, Cappelletti, Bruce Chesley, Christer Fuglesang and Giuseppe Governale, posted to the geoengineering research group as a multi-phase technology roadmap. It proposes a Planetary Sunshade System at the Sun-Earth L1 point, with precursor missions over roughly two decades, initial operations by 2040 and full deployment by 2080. The roadmap covers solar-sail design, in-space assembly, swarm logistics and launch infrastructure, and says political and regulatory questions, from international cooperation to public acceptance, need attention too.

The timetable explains why launch cost is the hinge. A shade large enough to matter needs mass in the millions of tonnes, and at today’s prices that is far out of reach. The roadmap’s bet is that reusable heavy-lift rockets will bring the price down far enough, over decades, to change the arithmetic.

SpaceX, whose rockets are the usual reference for that bet, is not involved in the report and did not respond to Nature’s query. Chief executive Elon Musk suggested in August on social media that “sentient satellites” could shade Earth, but it remains unclear whether he was serious.

The price tag skeptics point to

The skeptics have numbers. A critique from Geoengineering Monitor, a project of Biofuelwatch, ETC Group and the Heinrich Boell Foundation, says that launching a kilogram to low Earth orbit costs roughly $1,500 to $2,000, and that even at an optimistic $50 per kilogram a solar sail trimming sunlight by 1 percent would cost an estimated $5 trillion to $10 trillion. It notes that reducing incoming sunlight by about 2 percent would offset the warming from a doubling of carbon dioxide, so the shade would have to be very large.

That critique also lists risks beyond cost. Building a large structure could take millions of launches and burn enormous quantities of propellant. Structures near Earth risk collisions, and the effects on surface temperature, rainfall and crop yields are uncertain even at L1. A damaged shade could trigger termination shock, a sudden loss of cooling and abrupt rewarming, and none of the approaches reduces greenhouse-gas concentrations. Critics told Nature the focus on geoengineering also risks distracting from emissions cuts.

The disagreement is partly about timing. Cappelletti and the roadmap authors speak in decades, with deployment by 2080, while Visioni’s doubt reaches to the end of the century. Nature’s article, as summarized, states no launch-cost figure, no sunshade size and no total construction cost. The one number nobody has supplied is the one that decides the argument: a price per kilogram, and the date it is reached.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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