A British aid charity is warning that by 2060 more than a billion people worldwide will live in cities at risk of catastrophic flooding as a result of climate change. A study by Christian Aid says the US, China and India are among the countries most threatened. It says the Indian cities of Kolkata and Mumbai will be most at risk. The eight most vulnerable cities on the list are all in Asia, followed by Miami in the US. The report urges governments to take action to reduce global warming and invest in disaster reduction programmes. Dr Alison Doig, the report's author, told the BBC World Service that people living in large coastal cities were particularly at risk. "I think it's cities like Kolkata, Dakar, the big mega-cities of the south and the emerging economies where the people are most vulnerable to exposure to sea-level rises and to higher rain events," she said. "Flooding in these cities can cause massive damage, but can also threaten life." Dr Doig warned that Florida was likely to suffer extensive flooding. "The whole of Florida is totally vulnerable," she said. "It is so low-lying, it is virtually swampland reclaimed. So significant climate change... raising water half to a full metre this century, will take out an awful lot of Florida and a significant amount of Miami." The study says that the priority should be to rapidly reduce carbon emissions and limit temperature increase by switching from fossil fuels to low-carbon energy.

The massive bleaching hitting the Great Barrier Reef off the coast of Australia is likely that country's "biggest ever environmental disaster," says Dr. Justin Marshall, who has studied the reef for three decades. Only 7 percent of the reef has escaped bleaching, according to researchers at the ARC Center of Excellence. Marshall, a professor at the University of Queensland, says the destructive phenomenon is happening in an area the size of Scotland. "Before this mass bleaching started, we already were at the point of losing 50% of the coral cover on the Great Barrier Reef. This, I think, will probably take another 50% off what was left," Marshall says. Over the course of the last six months, Marshall and his colleagues with the citizen science project Coral Watch have documented the degradation of reef structures near Lizard Island, one of the worst-hit areas. They photographed the same formations of coral multiple times, showing clearly the pace of the destruction.

Any attempts to engineer the climate are likely to result in "different" climate change, rather than its elimination, new results suggest.

Prof Ken Caldeira, of Stanford University, presented research at a major conference on the climate risks and impacts of geoengineering.

These techniques have been hailed by some as a quick fix for climate change.

But the impacts of geoengineering on oceans, the water cycle and land environments are hotly debated.

They have been discussed at a meeting this week of 12,000 scientists in Vienna.

Researchers are familiar with the global cooling effects of volcanic eruptions, seen both historically and even back into the deep past of the rock record.

With this in mind, some here at the European Geosciences Union General Assembly have been discussing the possible worldwide consequences of pumping sulphate aerosols into the stratosphere to attempt to reflect sunlight back into space and cool the planet.