In October 2016, the world meteorological organization released a communique, which was the first time in 2015 that the global average concentration of carbon dioxide reached 400 parts per million.Last month, the record was renewed.The earth's atmospheric carbon dioxide concentration reached 410.28 parts per million on April 18, 2017, according to the us observatory in Hawaii.

That worries scientists working on climate change."Through emissions to slow global warming is essential, but may not be enough to reduce the risk for carbon emissions of climate. Climate change adaptation measures are equally important, but cannot solve all problems."On May 13, the university of Southampton, a professor at the school of ocean and earth science John Shepherd, global change and earth system science at Beijing normal university institute sponsored by the solar radiation management science and management conference calls.

Human beings have so far emitted 19m tonnes of carbon into the atmosphere.If you want to put the global average temperatures from pre-industrial levels are controlled within 2 ℃, henceforth carbon emissions must limit under 1 trillion tonnes of carbon;If you want to control the temperature within 1.5 ℃, the global carbon budget will be more nervous.

In John Shepherd's view, global warming will continue for decades, even if carbon emissions are reduced to zero today.But it will be a long time before humans are completely removed from fossil fuels.

To do this, scientists are trying to use solar radiation management (SRM) geoengineering to reduce the risk of global warming, in response to climate change and to take in a planned way, large-scale technical measures of changing the earth's environment.The main advice researchers are considering is to spray tiny reflective particles into the stratosphere.Or spray seawater into the lower atmosphere, the area created by the sea cloud, to increase the reflectivity of ocean clouds.

"The SRM is a theoretical proposal aimed at reducing the risk of global warming by blocking a small amount of sunlight to cool the planet."Beijing normal university, institute of global change and earth system science, chief scientist John Moore told reporters, the proceedings of the People's Republic of China "SRM is not a replacement for reducing greenhouse gas emissions, but if it into practice, will be quickly to slow, stop, or even the only known way to reverse the global warming."

John Shepherd said, however, the basis of current research model remains limited, uncertainty is high, the full impact of SRM is still poorly understood, such as the ozone layer, acid rain, PM2.5, the effects of global precipitation, etc.In addition, the physical impact is only a part of it, and it is more difficult to prove than natural science in terms of social and political science.

"It's a double risk tradeoff."John Moore says that not to be required to do SRM, but to consider an option to deal with climate risk.

Most of the research and discussion of the SRM in the past has been conducted in the developed world, with only a handful of Chinese scholars interested in international dynamics."China launched the first earth project in 2015, the 973 project."Chen ying, a researcher at the institute of urban development and environment of the Chinese academy of social sciences, said.

She said that the existing climate model simulation tools can be used to analyze the potential effect of SRM and other geoengineering, but research is relatively weak, especially in social science research, has not yet formed a complete knowledge system, lack of understanding of earth engineering support responsible decision making.

For this, Chen ying suggested, slow adaptation actions don't relax at the same time, the careful deployment of SRM geoengineering technologies such as development strategy, be included in the response to climate change strategy, strengthen the geoengineering research as the basis of scientific decision-making, and the complementary of natural science and social science which fusion, actively participate in international governance of earth project.