Former NASA scientist James Hansen, who was one of the first to raise concerns about climate change in the 1980s, has warned that sea levels could rise as much as 10 feet before the end of the century unless greenhouse gas emissions are drastically reduced. The rise would make cities such as London, New York and Shanghai uninhabitable. This comes as new data shows that this past June was the hottest on record, breaking the previous record, which was set last year.