Washington: Climate experts have warned that the world might have already reached the tipping point of climate change, where immediate actions needed to be done to reduce the effects of global warming. According to a report in Discovery News, the scientist who first put forward this theory is Nasa climate scientist James Hansen. Though Hansen had earlier warned about the dangers of climate change in 1988, his latest theory determines that "we have used up all slack in the schedule for actions needed to defuse the global warming time bomb.'