The threat to human health from climate change is so great that it could undermine the last 50 years of gains in development and global health, experts have warned. Extreme weather events such as floods and heat waves bring rising risks of infectious diseases, poor nutrition and stress, the specialists said. They said that polluted cities in which people work long hours and have no time or space for walking, cycling or relaxing are bad for the heart, and for respiratory and mental health.Almost 200 countries have set a 2C global average temperature rise from pre-industrial times as a ceiling to be achieved to limit the extent of climate change.But scientists say that the current trajectory could lead to a 4C rise in average temperatures, bringing risks of droughts, floods, storms and rising sea levels."That has very serious and potentially catastrophic effects for human health and human survival," said Anthony Costello, director of University College London's Institute for Global Health, who was a co-author of the report."We see climate change as a major health issue and that's often neglected in policy debates."The report was published by The Lancet...