airAir pollution in parts of China is now so extreme it could lead to conditions similar to a “nuclear winter,” scientists say. The smog that covers the country has become so thick it is impeding photosynthesis, potentially disrupting China’s food supply. China’s pollution problem is reaching crisis point, with acrid smog covering six southern provinces for the past week. Over the last few days a total of 19 cities have recorded levels of pollution drastically exceeding the World Health Organization’s (WHO) safety levels. Beijing’s concentration of micro-particles small enough to enter into people’s lungs and trigger serious health issues reached 505 micrograms per cubic meter Tuesday. The WHO’s safe level is 25 micrograms per meter. More