International rules are needed to govern intentional large-scale interventions in the Earth's natural systems to cool the planet, given unknown risks and consequences, experts said. They discussed the issue while participating in the fifth annual conference of the Taihu World Cultural Forum in Beijing, which concluded on Friday.

The sizzling temperatures in the northern hemisphere over the summer have been a reminder of climate change, and the weather extremes may be only the beginning of what scientists have been warning of for years, they said.

"Some scientists are now warning of a 'hothouse Earth' scenario, in which breaching the Paris temperature goals may set in motion other climate events that could effectively render large parts of the planet uninhabitable," said Janos Pasztor, executive director of the Carnegie Climate Geoengineering Governance Initiative, at a parallel event at the forum.

As the scale of the climate crisis becomes clearer, more senior policymakers are starting to ask whether humans can use large-scale interventions in the Earth's natural systems - such as large-scale carbon removal or solar geoengineering - to reduce the effects of climate change, Pasztor said.

Carbon removal involves removing carbon dioxide and other greenhouse gases for long-term isolation from the atmosphere. Solar geoengineering involves introducing highly reflective particles into the atmosphere to reflect more radiant energy back into space.

Pasztor, also former United Nations assistant secretary-general on climate change, said employing any such method on a large scale would have major consequences for the entire planet.

"Some of those consequences could be good, some could be bad, but whatever they are, the whole world will feel their effects, and will have a stake in their development.

"Yet at present there are no comprehensive international rules to govern them. This is a serious challenge we need to address," he said.

Stratospheric aerosol injection is the most talked about technology for solar geoengineering. Deliberate injection of aerosols into the upper atmosphere is an issue with impacts across the globe, he said.

"Depending on how the work is done, however, there can be impacts on different parts of the world," he said, adding more negative impacts may occur than positive ones in some regions, and a global agreement on the risk and benefit is needed.

He also said such interventions are not alternatives to carbon emissions reduction, adding, "The emissions reduction is the number one priority."

Geoengineering has been talked about and researched since the 1980s. The world now needs a governance system for it, said Qi Ye, director of the Brookings-Tsinghua Center for Public Policy.

"In essence, geoengineering resorts to interventions to address natural problems. In the history of humanity, we can find many examples of how trying to solve a natural problem resulted in many more troubles," he said.

Geoengineering needs to be done on a large scale to make it work, Qi said. Such a large-scale intervention, however, is without precedent.

Pan Jiahua, director of Institute for Urban and Environmental Studies of the Chinese Academy of Social Sciences, said solar geoengineering is more cost-efficient than carbon emissions reduction or carbon removal.

The method, which is theoretically possible, holds many uncertainties and humans should be cautious about using it, he said. Yet if the stability of the Earth's natural systems is in danger because of increasing temperatures, the world may face a choice between using the method and collapse, he said.