Environment

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California Gov. Jerry Brown, right, and former Gov. Arnold Schwarzenegger, left, talk before a climate bill signing on Treasure Island, Tuesday, July 25, 2017, in San Francisco. Gov. Jerry Brown signed legislation Tuesday keeping alive California's signature initiative to fight global warming, which puts a cap and a price on climate-changing emissions. The Democratic governor was joined by his celebrity predecessor, Arnold Schwarzenegger, who signed the 2006 bill that led to the creation of the nation's only cap and trade system to reduce greenhouse gases in all industries. (AP Photo/Eric Risberg)

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Virginia officials plan to use ground-penetrating radar to test the long-term stability of Natural Bridge, the landmark limestone arch that supports part of U.S. Route 11. Authorities are concerned about its continuing ability to support some 2,000 vehicles per day. (Associated Press)

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This image released by Paramount Pictures shows Al Gore in "An Inconvenient Sequel: Truth to Power." (Jensen Walker/Paramount Pictures via AP)

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FILE - In this undated file photo, pronghorns run through a field near Bismarck, N.D. North Dakota's pronghorn population and the popular hunting opportunity it provides both have taken a blow this year, with both wet and dry weather cited as reasons. Pronghorn numbers are down 14 percent from 2016, and the number of licenses being offered for the fall hunt is down 44 percent. The state's wildlife chief acknowledges it's a big setback. (Brian Gehring/The Bismarck Tribune via AP, File)

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In this undated photo provided by David Taylor Sr., former Marine David Taylor poses for an official portrait while in the Marine Corps. David Taylor Sr. told The Associated Press on Tuesday, July 25, 2017, that he was notified by the U.S. State Department that his son was killed earlier this month in Syria while fighting for a Kurdish militia battling the Islamic State group. (U.S. Marine Corps/David Taylor Sr. AP)

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This image released by Paramount Pictures shows Al Gore in "An Inconvenient Sequel: Truth to Power." (Jensen Walker/Paramount Pictures via AP)

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This image released by Paramount Pictures shows Al Gore in "An Inconvenient Sequel: Truth to Power." (Jensen Walker/Paramount Pictures via AP)

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Broken sea ice emerges from under the hull of the Finnish icebreaker MSV Nordica as it sails through the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. Sea ice forms when the top layer of water reaches freezing point, usually around the start of October. As temperatures continue to fall this first-year ice grows downward until it is several feet thick. If the ice survives the following summer melt it becomes second-year ice. Another cycle and it becomes multi-year ice, which is the toughest kind. (AP Photo/David Goldman)

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Broken sea ice emerges from under the hull of the Finnish icebreaker MSV Nordica as it sails through the Franklin Strait while traversing the Arctic's Northwest Passage, Saturday, July 22, 2017. Sea ice forms when the top layer of water reaches freezing point, usually around the start of October. As temperatures continue to fall this first-year ice grows downward until it is several feet thick. If the ice survives the following summer melt it becomes second-year ice. Another cycle and it becomes multi-year ice, which is the toughest kind. (AP Photo/David Goldman)

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Broken sea ice emerges from under the hull of the Finnish icebreaker MSV Nordica as it sails through the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. (AP Photo/David Goldman)

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Water sprays as a block of sea ice is broken from the hull of the Finnish icebreaker MSV Nordica as it sails the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. (AP Photo/David Goldman)

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A block of sea ice floats in the Franklin Strait in the wake of the Finnish icebreaker MSV Nordica as it sails the Arctic's Northwest Passage, Saturday, July 22, 2017. Sea ice forms when the top layer of water reaches freezing point, usually around the start of October. As temperatures continue to fall this first-year ice grows downward until it is several feet thick. If the ice survives the following summer melt it becomes second-year ice. Another cycle and it becomes multi-year ice, which is the toughest kind. (AP Photo/David Goldman)

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Broken sea ice emerges from under the hull of the Finnish icebreaker MSV Nordica as it sails through the Franklin Strait while traversing the Arctic's Northwest Passage, Saturday, July 22, 2017. (AP Photo/David Goldman)

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A block of sea ice floats in the wake of the Finnish icebreaker MSV Nordica as it sails through the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. Sea ice forms when the top layer of water reaches freezing point, usually around the start of October. As temperatures continue to fall this first-year ice grows downward until it is several feet thick. If the ice survives the following summer melt it becomes second-year ice. Another cycle and it becomes multi-year ice, which is the toughest kind. (AP Photo/David Goldman)

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Broken sea ice emerges from under the hull of the Finnish icebreaker MSV Nordica as it sails through the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. As a general rule, the older ice gets the more it turns blue and acquires mounds, so-called hummocks, on top from years of crashing into other floes. (AP Photo/David Goldman)

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The bow of the Finnish icebreaker MSV Nordica pushes down sea ice as it sails through the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. The MSV Nordica is equipped with several heavy-duty engines and a hardened bow and hull that allow it either to drive through thin layers of ice or to crush thicker sheets by rising onto the ice with the help of its rounded hull. The ship's massive weight breaks the ice from above. (AP Photo/David Goldman)

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The bow of the Finnish icebreaker MSV Nordica drives through sea ice as it sails the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. The MSV Nordica is equipped with several heavy-duty engines and a hardened bow and hull that allow it either to drive through thin layers of ice or to crush thicker sheets by rising onto the ice with the help of its rounded hull. The ship's massive weight breaks the ice from above. (AP Photo/David Goldman)

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Broken sea ice emerges from under the hull of the Finnish icebreaker MSV Nordica as it sails through the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. (AP Photo/David Goldman)

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Broken blocks of sea ice emerge from under the hull of the Finnish icebreaker MSV Nordica as it sails through the Victoria Strait while traversing the Arctic's Northwest Passage, Friday, July 21, 2017. Sea ice forms when the top layer of water reaches freezing point, usually around the start of October. As temperatures continue to fall this first-year ice grows downward until it is several feet thick. If the ice survives the following summer melt it becomes second-year ice. Another cycle and it becomes multi-year ice, which is the toughest kind. (AP Photo/David Goldman)

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A block of sea ice floats in the Victoria Strait in the wake of the Finnish icebreaker MSV Nordica as it sails the Arctic's Northwest Passage, Friday, July 21, 2017. Sea ice forms when the top layer of water reaches freezing point, usually around the start of October. As temperatures continue to fall this first-year ice grows downward until it is several feet thick. If the ice survives the following summer melt it becomes second-year ice. Another cycle and it becomes multi-year ice, which is the toughest kind. (AP Photo/David Goldman)