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."

New data on carbon shows that China's emissions per head of population have surpassed the EU for the first time. The researchers say that India is also forecast to beat Europe's CO2 output in 2019. Scientists say that global totals are increasing fast and will likely exceed the limit for dangerous climate change within 30 years. The world has already used up two thirds of the warming gases researchers calculate will breach 2 degrees C. The Global Carbon Project involves researchers from several different institutes around the world and it provides objective details on the scale of annual emissions. The latest data shows that a record 36 billion tonnes of carbon from all human sources were emitted in 2013. Top ten emitters 2013 - % of global total China - 29 USA - 15 EU - 10 India - 7.1 Russian Federation - 5.3 Japan - 3.7 Germany - 2.2 Republic of Korea - 1.8 Iran - 1.8 Saudi Arabia - 1.5 The biggest emitters were China, which produced 29% of the total, followed by the US at 15%, the EU at 10% and India at 7.1% But in an interesting development, China's emissions per head of population exceeding those of the European Union for the first time. While the per capita average for the world as a whole is 5 tonnes of carbon dioxide, China is now producing 7.2 tonnes per person, to the EU's 6.8 tonnes. The US is still far ahead on 16.5 tonnes per person. "We now see China's per capita emissions surpassing the EU," said Dr Robbie Andrew, from the Centre for International Climate and Environmental Research in Norway, who was involved in the research.

The WMO says that fossil fuel activities such as oil refining are driving atmospheric levels of CO2 to record highs. The levels of gases in the atmosphere that drive global warming increased to a record high in 2012. According to the World Meteorological Organization (WMO), atmospheric CO2 grew more rapidly last year than its average rise over the past decade. Concentrations of methane and nitrous oxide also broke previous records. Thanks to carbon dioxide and these other gases, the WMO says the warming effect on our climate has increased by almost a third since 1990. The WMO's annual greenhouse gas bulletin measures concentrations in the atmosphere, not emissions on the ground. Carbon dioxide is the most important of the gases that they track, but only about half of the CO2 that's emitted by human activities remains in the atmosphere, with the rest being absorbed by the plants, trees, the land and the oceans. Since the start of the industrial era in 1750, global average levels of CO2 in the atmosphere have increased by 141%. According to the WMO there were 393.1 parts per million (ppm) of carbon dioxide in the atmosphere in 2012, an increase of 2.2ppm over 2011. This was above the yearly average of 2.02ppm over the past decade. "The observations highlight yet again how heat-trapping gases from human activities have upset the natural balance of our atmosphere and are a major contribution to climate change," said WMO Secretary-General Michel Jarraud.