China and Russia have modified an important layer of the atmosphere above Europe to test a controversial technology for possible military application, according to Chinese scientists involved in the project.

A total of five experiments were carried out in June. One, on June 7, caused physical disturbance over an area as large as 126,000 sq km (49,000 square miles), or about half the size of Britain.

The modified zone, looming more than 500km (310 miles) high over Vasilsursk, a small Russian town in eastern Europe, experienced an electric spike with 10 times more negatively charged subatomic particles than surrounding regions.

The particles, or electrons, were pumped into the sky by Sura, an atmospheric heating facility in Vasilsursk built by the former Soviet Union’s military during the cold war.

In the China-Russian experiment, researchers found that even with a small power output of 30MW, the radio beam could create a large abnormal zone. But they also found that the effects dropped sharply after sunrise, as the man-made perturbation easily became lost in the noise created by sunlight.

China and Russia band together on controversial heating experiments to modify the atmosphere

“We are not playing God. We are not the only country teaming up with the Russians. Other countries have done similar things,” said another researcher who was involved in the project and asked not to be named because of the sensitivity of the issue.

The Sura facility has also conducted joint research with France and the United States, according to papers published in academic journals.

The National Centre for Space Studies, a French government agency under the supervision of the ministries of defence and research, has deployed the micro satellite Demeter to monitor Sura’s radio emissions.

The Defence Meteorological Satellite Programme run by the US Department of Defence also contributed fly-by data in several heating experiments conducted at the Russian site before 2012.

The countries were willing to collaborate in part because many scientific and technical problems remain to be solved, the Chinese researcher said.

Professor Gong Shuhong, a military communication technology researcher at Xidian University, formerly the Radio School of the Central Military Committee, said he had been closely following the Russia-China heating experiment.

“The energy emitted was too low to trigger a global environmental event,” he said. “Human influence is still very small compared to the power of Mother Nature. But the impact to a small region is possible.”

China and Russia band together on controversial heating experiments to modify the atmosphere

In theory, a butterfly flapping its wings might be amplified in a sophisticated weather system and cause a storm in a distant location several weeks later.

“Such studies must strictly follow ethical guidelines,” Gong said. “Whatever they do, it must not cause harm to the people living on this planet.”