1. How China finessed a rain-free Olympics ceremony

When Beijing hosted its first Olympics back in August 2008, nothing was going to rain on its parade, even though there was a 50% chance of showers at that time of year. If rain threatened, Beijing’s Weather Modification Office, part of the China Meteorological Administration, was ready to deploy two planes and 20 rocket-launcher and artillery sites outside the capital to fire off rounds of silver iodide and dry ice. This would force water particles to agglomerate around the silver iodide and be released as rain before the clouds neared the Bird’s Nest stadium.

It worked. Chinese media reported that on 8 August 2008, engineers launched 1104 rain dispersal rockets between 4pm and 11.39pm and the ceremony took place under clear skies.

2. Rain-making on an epic scale

The Chinese have much bigger ambitions than running rain-free events. In 2018, Forbes magazine reported that China’s state-owned Aerospace Science and Technology Corporation was rolling out thousands of rain-inducing ‘machines’ – actually a network of chambers – across the Tibetan Plateau, the source of the Yangtze, Yellow and Mekong rivers. The chambers burn solid fuel to produce silver iodide particles that promote precipitation.

Researchers expected the system to produce up to 10 billion cubic metres of rainfall each year, equal to about 7% of China's annual water consumption.

In December 2020, China’s government announced that by 2025 it would increase the cloud-seeding region to 5.5 million square kilometres, an area more than 1.5 times the size of India.

3. It’s illegal to use the weather as a weapon

Believe it or not, there’s an international treaty that prohibits using weather as a weapon. The Environmental Modification Convention (ENMOD) prohibits the hostile use of any environmental modification techniques leading to long-lasting or severe effects. The United Nations Convention was opened for signatories in 1977 and came into force in October 1978.

4. Solar radiation management could cool the planet (in theory)

Global temperatures tend to dip after major volcanic eruptions because the ash and sulphur ejected into the atmosphere dims the sun’s rays. In theory, a similar principle could cool global warming. Injecting aerosols such as sulphur dioxides, finely powdered salt or calcium carbonate into the atmosphere could bounce back the Sun’s radiation and reduce temperatures. But it’s not without danger. Computer simulations suggest such actions could cause droughts in Africa and Asia, warns the Geoengineering Monitor. A global reduction in carbon emissions is the safer route.

5. Aircraft contrails affect the temperature

Contrails, that cloudy exhaust behind jets, can affect temperature. If the air is cold enough, the water droplets and soot from jet engines freeze to make a thin ice cloud, called a contrail cirrus cloud. In areas with dense air traffic, those clouds can join together.

US researchers found that, just like natural clouds, contrail cirrus clouds lift night-time temperatures because warmer air gets trapped beneath the cloud. That can reduce the daily temperature range by up to 3°C.

Contrail cirrus clouds last only hours, but researchers from Germany’s Institute of Atmospheric Physics warn they contribute to global warming. Bernd Kärcher told Yale Environment 360 that contrails could add “as much as a tenth of a degree [to global temperatures] by mid-century.”

Flying aircraft where the air is warmer – at lower altitudes and during the day – would avoid contrail cirrus clouds forming.

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