Controlling the Weather
Discover how we make rain and the ambitious plans being hatched to tackle climate change.
Superhero Storm in the X-Men comics can conjure rain, end droughts and create hurricanes with the power of her mind. Now, scientists and meteorological technology are opening more and more opportunities for us mere mortals to manipulate weather and Earth’s climate. In 2009, Chinese meteorologists from the Beijing Weather Modiﬁcation Ofﬁce claimed to be responsible for the city’s earliest snowfall since 1987. Around 16 million tons of snow reportedly fell over drought-afflicted northern China after workers ﬁ red rockets carrying pellets of silver iodide into heavy clouds.
The rockets were cloud seeding, a process invented in the late-Forties. Supporters claim it can reduce hail damage, increase rainfall and disperse fog among other things. There are cloud-seeding projects in at least 20 countries worldwide, from Israel to Australia; in 2003, in the US alone, ten states were conducting at least 66 cloud-seeding programmers. In China, around 32,000-35,000 people are employed in the weather modiﬁcation industry.
The big question in cloud seeding is: how effective is it? A 2003 US National Academies report concluded there was no concrete scientiﬁ c proof it worked. According to Professor Michael Garstang from the University of Virginia, who chaired the report, the situation hasn’t changed much since; there remains “a lack of deﬁnitive evidence,” he says. Even cloud-seeding supporters admit it doesn’t currently lead to a huge rise in rain and snowfall. “It doesn’t increase precipitation by 50 per cent in most cases,” says Bruce Boe from Weather Modiﬁcation Inc, a private weather control company based in North Dakota, USA. US enthusiasm for weather modiﬁcation research waned in the late-20th century, with funding falling to less than ﬁve per cent of its Seventies peak. But there are signs of fresh interest in the ﬁeld. The US National Science Foundation (NSF) is funding a cloud-seeding project in the Wyoming mountains, operated by Weather Modiﬁ cation Inc. New technology, such as advanced computer models and radar instruments that can see inside clouds is driving the resurgence of interest, says Boe: “We’re bringing a lot of new tools to bear on the question. These tools weren’t available before and they’re starting to bear fruit.”
The Wyoming project, launched in 2005, uses aircraft-mounted radar and ground-based instruments. It tests the effectiveness of seeding winter orographic clouds – which are cold clouds formed when air rises over mountains – with silver iodide. ”In the mountains of the American West, these types of storms are the main target for cloud seeding. Often the clouds are not efficient at generating snow, so cloud seeding is used to enhance snow production,” says Dan Breed from the US National Center for Atmospheric Research (NCAR), who is evaluating the project. Another aim of the experiment is to increase snowfall by perhaps ten per cent a year, building up the winter snowpack so it’s available for use. The extra water running off the mountains each spring would be worth an estimated £1.5-3 million ($2.4-$4.9 million). Cloud seeding affects the weather in a local region, but there are other technologies being devised to alter climate on a much bigger scale.
Space mirrors and giant ﬂoating hosepipes might sound far-fetched, but they’re two proposals for geoengineering. Geoengineering is deliberate global modiﬁcation of Earth’s climate to counter man-made climate change. Geoengineering may sound impossible, but serious scientists are investigating how it might cool down the planet. In the last few years, billionaire Bill Gates reportedly donated £2.8 million ($4.5 million) to geoengineering research, and the UN IPCC report, a summary of what most scientists agree we know about climate change, mentioned geoengineering for the ﬁrst time this year.
Geoengineering is essentially ‘Plan B’ in case we reduce greenhouse gas emissions ‘too little, too late’ to avoid dangerous climate change, argues a 2009 report by the UK’s Royal Society. A temperature rise of just two degrees Celsius (3.6 degrees Fahrenheit) could melt the Greenland ice sheet and cause a long-term sea level rise of seven metres (23 feet). That’s enough water to submerge both London and Los Angeles.
To avoid this wide-scale warming, we’d need to cut global carbon dioxide emissions by 50 per cent of 1990 levels by 2050, according to the Royal Society. Yet emissions are still rising – by 1.4 per cent during 2012. Even if we cut carbon emissions today, temperatures will continue rising for decades. The climate system is like an oil tanker – ie slow to turn around. Dr Hugh Hunt is an engineer from Cambridge University working on SPICE (Stratospheric Particle Injection for Climate Engineering) – a UK government-funded geoengineering research project: “We don’t know what the scale of unabated climate change will be,” he says. “You’ve got to think in advance what emergency measures you might need, and then hope you won’t need them.”
There are two types of geoengineering.
Solar radiation management (SRM) cools the Earth by reﬂecting the Sun’s heat back into space, while carbon dioxide removal (CDR) scrubs CO2 – the primary greenhouse gas causing man-made climate change – from the atmosphere. Examples of SRM include space mirrors, injecting sulphate aerosols into the atmosphere through giant hosepipes and painting urbanroofs white. One idea uses cloud seeding to make clouds more reﬂective. Fleets of unmanned barges could sail the oceans, spraying clouds with saltwater. Salt particles should create more water droplets in the clouds, whitening them. Proposals for CDR include fertilising tiny marine plants with iron, growing new forests or fast-growing crops and burying charcoal, all of which lock up CO2 and remove it from the air. Most geoengineering proposals remain concepts at this stage.
“We can do very little right now because the technology hasn’t been developed to intervene on a planetary scale,” notes Dr Andy Parker, a researcher into solar geoengineering from Harvard University.
Still, there are a few examples of outdoor ﬁeld tests. The SPICE project included a plan, later abandoned, to pump water one kilometre (0.6 miles) vertically through a pipe attached to a helium balloon. Its aim was to test the feasibility of squirting sulphate aerosols into the sky through a giant hosepipe. “We don’t know if it’s technically possible,” continues Dr Hunt. “No one has built a 20-kilometre (12-mile) pipe that goes vertically upwards.” The questions are: can we build and launch a balloon big enough, and secondly, can we build a pipe strong enough?
Other geoengineering proposals rely on pre-existing technology. Fertilising oceans with iron, for example, has already happened on a small scale although not necessarily legally. It needs lots of tanker ships, chemical plants and iron. “There’s nothing technically difﬁ cult about that,” says Professor Andy Ridgwell from Bristol University. It would take hundreds of years to see results from iron fertilisation and other CDR technologies though. They rely on slow natural processes, such as fertilizing tiny marine plants that transport carbon into the deep ocean when they die. “You can’t suddenly pull loads of CO2 out of the atmosphere with any of them,” explains Professor Ridgwell. “They lend themselves to gradual mitigation.” Growing vast new forests or fast-growing crops competes with existing land uses, explains Dr Tim Lenton from Exeter University.
The idea is to repeatedly harvest fast-growing crops like eucalyptus, which capture the CO2 they use to grow. But we want to use the best soils to grow food. “The plausibility problem is that you’re in potential competition with other land uses in a world where dietary demands are rocketing.” Reﬂecting sunlight back into space with aerosols is the fastest geoengineering method.
It mimics the rapid cooling effect of a large volcanic eruption. “Once you start blocking out some sunlight, temperatures drop quite quickly,” explains Andy Parker. For example, in the two years after the eruption of Mount Pinatubo in the Philippines in 1991, global temperatures cooled by about 0.5 degrees Celsius (0.9 degrees Fahrenheit) on average. So realistically how fast could we cool the planet? Dr Hunt concludes: “Let’s suppose the Greenland ice sheet completely melts and we get a one-metre [3.2-foot] sea-level rise. It could be done in ﬁve years – if we’ve got time to think about it, 20-30 years from now.”
Weather-changing tech in action
Discover the machines and techniques capable of adapting Earth’s climate
A giant sunshade made of tiny mirrors could be put into orbit to cool the Earth. Taking decades and trillions of dollars to deploy, its effect on our weather is unknown and it would not stop the oceans acidifying.
Painting roofs white and brightening roads/pavements should help bounce the Sun’s heat back into space and cool the Earth, but some scientists believe white roofs could reduce cloud formation and increase warming.
This would involve spreading crushed olivine – a silicate mineral – over agricultural land, which chemically reacts with CO2 to produce alkaline limestone; this could then be used in the ocean to reduce acidity. A simple idea, but would require huge mining and chemical plants.
These towering machines would scrub carbon dioxide from the air, turning it into liquid that can be stored in porous rocks beneath the oceans. Millions of artiﬁcial trees would be needed and the CO2 needs storing for millions of years.
Certain crops, shrubs and grass reﬂect more sunlight back into space than others. This would be cheap to implement, but needs a huge land area and has unknown effects on food prices, plant growth, disease and drought resistance.
Biochar is charcoal produced by ‘cooking’ plants or manure with little or no oxygen. It is decay-resistant and can store carbon in soil for thousands of years. Useful on a small scale, but growing biochar crops conﬂicts with the demand for food and biofuel production.
Regrowing trees in previously forested areas to increase the carbon dioxide they absorb is cheap and safe, but conﬂicts with the ever-rising demand for agricultural land for food and energy production.
Hosepipes attached to giant helium balloons would spray particles high into Earth’s atmosphere to mimic the cooling effect of volcanic eruptions. For example, aerosols released by the 1991 Mount Pinatubo eruption cooled global temperatures by an average 0.5°C (0.9°F). The proposed balloons would be the largest and tallest man-made structures in history.
Cloud seeding is a technique for manmade rainmaking already used around the world to varying degrees of success. Rainfall naturally occurs when water droplets attach to sand, dust or salt particles. Cloud seeding squirts extra particles into clouds to spawn new raindrops. Salt is used in warm tropical clouds, while silver iodide is added to cold clouds to create extra ice crystals. Some scientists believe cloud seeding can brighten clouds to counteract climate warming too. The extra particles make the clouds denser, whiter and more reﬂective, deﬂecting more sunlight back into space.
Marine plant life is at the core of the ocean food chain. The plants are a source of food for other marine life, and happen to take up and bind carbon dioxide as well. They rely on the availability of nutrients to grow – most commonly nitrogen or iron. Fertilizing the oceans with iron sulphate is believed to increase their growth and reproduction, which would in turn increase the amount of carbon dioxide they take up, reducing the effect of carbon emissions. Some scientists also believe that the increased marine plant life may increase the number of ﬁsh in the sea, in turn improving our food supply.
The Risk of Geo-engineering
Geo-engineering is controversial because it involves large-scale changes to Earth’s climate. Critics discuss possible negative side effects, like that ocean fertilisation might cause toxic algal blooms, or that geoengineering gives industry and government excuses not to cut carbon emissions. Geoengineering also raises issues of ethics. Cooling the climate with sulphate aerosols “is potentially cheap enough for single countries to do”, says Professor Andy Ridgwell, Bristol University, but could impact other countries’ climates as well. Others fear ‘rogue’ geoengineers. For example, an American businessman dumped 100 tons of iron sulphate into the Pacific in July 2012 in an unauthorised ocean fertilisation scheme.