This photo from 2007 shows a man and woman looking at the city skyline from a coastal defense breakwater in Alexandria, Egypt. Sea levels rising because of global warming, along with increased storminess as the climate changes, will expose tens of millions of people in the world's port cities to coastal flooding, says a report by the Organization for Economic Cooperation and Development. Ben Curtis/AP/File
Flood waters cover restaurant tables near the lion column in Saint Mark's square in Venice, Italy on December 1, 2008. Large parts of Venice were flooded as heavy rains and strong winds lashed the lagoon city, with sea levels at their highest level in 22 years. Ferry and water taxi services in the city were suspended and Venice's mayor urged people to stay indoors. Tourists and residents struggled to get across the city over raised walkways.
In this photo taken Sept. 29, residents travel in passenger canoes through Makoko, a slum neighborhood built on stilts over Lagos Lagoon in Lagos, Nigeria. Rising seas put the neighborhood at risk. Sunday Alamba/AP
This Sept. 30 photo shows shanties in Dharavi, one of the world's largest slums, in Mumbai, India. The slum is just above sea level putting it at risk of flooding if sea levels continue to rise. Rajanish Kakade/AP
In this Sept. 9 photo, water lock station employees observe the water lock in Suzhou Creek in Shanghai, China. Shanghai sits roughly 10 feet above sea level and is among dozens of great world cities, including London, Miami, New York, New Orleans, Mumbai, Cairo, Amsterdam, and Tokyo, threatened by sea levels that now are rising twice as fast as projected just a few years ago, expanding from warmth and meltwater. Eugene Hoshiko/AP/File
The promenade around Battery Park City in lower Manhattan is only a few feet above sea level. During a major storm the area would flood. Melanie Stetson Freeman/The Christian Science Monitor/File
As the climate warms and sea levels rise, Dutch visionaries in the Netherlands foresee hundreds of thousands of people living in 'floating' cities. A hint of what the future could bring lies in Amsterdam, where conventional-looking homes are built on Styrofoam platforms that rise with the tide or flood waters. Susan Taylor Martin/Newscom/File
A model of Manhattan shows the effect of rising sea levels. The model you see here doesn't predict the future, but it does illustrate one possible outcome of polar ice sheet meltdown. It shows the southern end of Manhattan Island, a borough currently home to more than 1.5 million people, under 10 or 16 feet of water. Newscom/File
This photo shows the Canadian Arctic community of Tuktoyaktuk in the Northwest Territories, Canada. Seas rising from global warming and land sinking as permafrost thaws are threatening the Canadian Arctic community. A beach barrier of small boulders has slowed the erosion of the peninsula (upper left). Geologists believe the protective Tuktoyaktuk Island (upper right) will erode away in 30-40 years, exposing the hamlet more to Arctic Ocean waves. Government of Northwest Territories/AP/File
This Sept. 29 photo shows people taking a stroll at Nariman Point, an area reclaimed from the sea which is now the lower tip of the city, in Mumbai, India. The area is at risk of being re-submerged if sea levels increase. Rajanish Kakade/AP/File
In this photo taken on April 18, the Sumida River is seen in Tokyo, Japan. Sea levels rising because of global warming, along with increased storminess as the climate changes, will expose tens of millions of people in the world's port cities to coastal flooding, says a report by the Organization for Economic Cooperation and Development. Shizuo Kambayashi/AP/File
This 2007 photo shows swans in front of the closed Maeslant Barrier gates in the Nieuwe Waterweg near Hoek van Holland, the Netherlands. Approximately 27 percent of the country, home to 60 percent of its residents, is below sea level. Bas Czerwinski/AP/File
A stone wall is created in Wales in order to delay the impact of rising sea levels. Newscom/File
A monitoring station in Hawaii has measured carbon dioxide levels of 400 parts per million, a concentration not seen on Earth since the Pleistocene Era.
Worldwide levels of the chief greenhouse gas that causes global warming have hit a milestone, reaching an amount never before encountered by humans, federal scientists said Friday.
/Photo-Galleries/In-Pictures/From-Field-to-Fork-The-foreign-and-domestic-food-chain
/Photo-Galleries/Photos-of-the-Day/2013/Photos-of-the-day-07-17
/Photo-Galleries/In-Pictures/Around-the-world-with-John-Kerry
/Photo-Galleries/In-Pictures/Where-Our-Clothes-Come-From
/Photo-Galleries/In-Pictures/Wildfires-2013
/Photo-Galleries/In-Pictures/Facebook-fans-caption-Monitor-photos
/Photo-Galleries/Photos-of-the-Day/2013/Photos-of-the-day-07-16
/Photo-Galleries/In-Pictures/The-kings-and-queens-of-modern-monarchies
/Photo-Galleries/Photos-of-the-Day/2013/Photos-of-the-day-07-15
/Photo-Galleries/In-Pictures/Confronting-doping-in-sports
/Photo-Galleries/In-Pictures/Which-side-of-the-fence-are-you-on-The-US-immigration-debate
/Photo-Galleries/Photos-of-the-Day/2013/Photos-of-the-Day-07-14