By: Associated Press

On the defensive over a trio of controversies, President Barack Obama refocused the debate Thursday with a speech laying out his administration's rationale for the use of unmanned drone strikes against terrorism targets abroad.

WASHINGTON -- President Barack Obama on Thursday defended America's controversial drone attacks as legal, effective and a necessary linchpin in an evolving U.S. counterterrorism policy. But he acknowledged the targeted strikes are no "cure-all" and said he is haunted by the civilians unintentionally killed.

The president also announced a renewed push to close the Guantanamo Bay detention center in Cuba, including lifting a moratorium on prisoner transfers to Yemen. However, shutting the prison will still require help from Republicans reluctant to back Obama's call to move some detainees to U.S. prisons and try them in civilian courts.

Obama framed his address as an attempt to redefine the nature and scope of terror threats facing the U.S., noting the weakening of al-Qaida and the impending end of the U.S. war in Afghanistan.

"Neither I, nor any president, can promise the total defeat of terror," Obama said in remarks at the National Defense University. "What we can do -- what we must do -- is dismantle networks that pose a direct danger, and make it less likely for new groups to gain a foothold, all while maintaining the freedoms and ideals that we defend."

Since taking office, Obama's counterterrorism strategy has increasingly relied on the use of strikes by unmanned spy drones, particularly in Pakistan and Yemen. The highly secretive program has faced criticism from congressional lawmakers who have questioned its scope and legality.

By: Martin Weitzman

No one can say with any assurance what the dollar value of damages would be from the highly uncertain climate changes that might accompany a planet earth that is steadily warming.

Paul Solman: Are headlines trumpeting the fact that carbon dioxide levels in the earth's atmosphere have now passed 400 parts per million for the first time in something like three million years unduly alarmist? Or are they a timely warning?

I asked noted environmental economist Martin Weitzman to address the question.

An expert on the Soviet economy in the '70s and '80s, Weitzman first made news in 1984 with the publication of a book called The Share Economy, an argument for profit sharing instead of fixed wages. Fourteen years later came his paper Recombinant Growth, which revolutionized how some of us understood the enormous potential of technology.

But for many years, Weitzman has also been working on environmental economics and most recently, in a series of widely cited academic papers, on the economics of global warming; the most famous, on the "Economics of Catastrophic Climate Change."

Weitzman's central idea is not unlike the legendary bet proposed by the 16th century Catholic French philosopher Blaise Pascal. One way to interpret Pascal's argument: even if you think the likelihood of God's existence is vanishingly small, the cost if you're wrong -- eternal damnation -- is infinitely high. An infinite cost times even a tiny probability is still ... an infinite cost.

So you make a finite investment by believing in God and acting accordingly in order to avoid an infinite cost. To put it another way, you're obliged, mathematically, to make the investment in belief.

You might keep Pascal's argument in mind while reading Weitzman. Or think of the "Black Swan" argument of Nassim Taleb: certain events, however unlikely you think they may be, could have such enormous consequences, you just can't take the chance of letting them happen.

Martin Weitzman: Recently the concentration of atmospheric carbon dioxide (CO2) reached an unprecedented level of 400 parts per million. What is the significance of this "milestone"? Does it portend catastrophic climate change? The short answer is no. The long answer is a more complicated and more nuanced maybe.

By: Rebecca Jacobson

An American flag stands amid the rubble of the May 20 tornado that tore through Moore, Okla. Photo by Rebecca Jacobson.

I've driven through Oklahoma many times, usually once or twice a year as my family traveled from our home in Omaha, Neb., to visit relatives in Dallas. And every Valentine's Day, I'd cross through Moore on the way to visit my boyfriend, who was a graduate student in the nearby city of Norman.

On Tuesday, I returned to Moore, having been given the rare opportunity to join the organization Save the Children on a two-hour tour of the tornado damage.

The city I'd come to know was unrecognizable.

Debris was everywhere I looked and yet at first glance it all looked like nothing -- an incomprehensible mass of rubble. But slowly, I began to identify things: an overturned clawfoot bathtub, remote controls, toys, street signs, dishes. A mess of twisted metal was formerly the front end of a BMW; the spot where I stood was once someone's house. Metal guard rails wrapped around the few remaining telephone poles and trees like twist ties. The wall of one home had been sheared off, leaving a bedroom exposed. The sheets were still on the bed.

Residents silently picked through the rubble, collecting what belongings they could.

Across Telephone Road was Moore Medical Center. The top floor, which used to house the maternity wing, was gone. Walls of the building had collapsed. Windows had shattered. Dozens of crumpled vehicles were stacked in the medical center's parking lot. Emergency personnel had marked the destroyed vehicles with pink and orange paint to show that each had been searched for victims.

Sgt. Johnny Hernandez of the Dibble Police Department pointed to a black mark where a car had slammed into the hospital during the storm, blocking the exit door. He was here during the tornado of 1999, too. At least the storm left the pavement intact this time, he said.

"I think I've seen enough storms for a while," he added.

By: News Desk

Correspondent Gwen Ifill answered questions during a live chat, hosted by PBS' Washington Week.

Read through the chat below.

By: Michael D. Mosettig

Screen grab of Chinese skyline.

In the small town writ large of Washington, eight city blocks can separate a wide gulf of hopes and fears about future relations between the world's two major economic powers -- the United States and China.

In a large conference room at the Center for Strategic and International Studies, jammed with business executives, think tankers and Asian journalists, a high powered group of Chinese and U.S. business leaders and former officials presented a report calling for deeper cooperation to nurture and expand "the most important (economic relationship) in the world" over the coming decade. The trading volume between the countries has grown to half a trillion dollars.

Two hours later, a small group of reporters clustered at the National Press Building for a presentation of a report of the Commission on the Theft of American Intellectual Property asserting China is responsible for up to 80 percent of the $300 billion theft of intellectual property from companies in the Untied States and other advanced economies.

By: Associated Press

Watch a live stream in the player above of President Barack Obama's speech at the National Defense University, scheduled to begin at 2 p.m. EDT Thursday.

WASHINGTON (AP) -- President Barack Obama is set to at least partially lift the veil of secrecy surrounding U.S.-directed drone strikes around the world, a key component of counterterrorism strategy, as he outlines the contours of the continuing threat to American security.

On the eve of the president's speech at the National Defense University, the Obama administration revealed for the first time that a fourth American citizen had been killed in secretive drone strikes abroad. The killings of three other Americans in counterterror operations since 2009 were widely known before a letter from Attorney General Eric Holder to Senate Judiciary Committee Chairman Patrick Leahy acknowledged the four deaths.

Obama's speech is expected to reaffirm his national security priorities - from homegrown terrorists to killer drones to the enemy combatants held at the military-run detention center at Guantanamo Bay, Cuba - but make no new sweeping policy announcements.

The White House has offered few clues on how the president will address questions that have dogged his administration for years and, critics say, given foreign allies mixed signals about U.S. intentions in some of the world's most volatile areas.

By: Terence Burlij

Undated image courtesy of the U.S. Air Force shows a MQ-1 Predator unmanned aircraft. Photo: REUTERS/U.S. Air Force/Lt Col Leslie Pratt

On the defensive over a trio of controversies, President Barack Obama will attempt to refocus the debate Thursday with a speech laying out his administration's rationale for the use of unmanned drone strikes against terrorism targets abroad.

The president's address at the National Defense University in Washington comes as the administration has faced mounting pressure at home and abroad to provide greater transparency when it comes to its counterterrorism policies. In his remarks Mr. Obama is expected to outline a legal and policy justification for conducting drone strikes and respond to questions raised by the use of targeted killings, according to a White House official.

The administration took an initial step Wednesday in its revamped approach to the sharing of information related to national security operations when Attorney General Eric Holder sent a letter to members of Congress acknowledging the killing of four U.S. citizens in overseas drone attacks.

By: Colleen Shalby

Anita Lebya found this photo of she and her husband Jim through the Lost Photos of Joplin National Disaster Photo Rescue after a 2011 tornado in Joplin, Mo. Photo courtesy of Anita Lebya.

Not long after a tornado tore through Oklahoma on Monday, Facebook groups began to spring up with posts showing tarnished photos discovered in scattered debris miles away. Unclaimed memories, laid out before strangers in the hopes of catching a recognizing glimpse.

It's not the first time that lost and found sites on social media have been created after a natural disaster. Two years ago, on May 22, 2011, similar Facebook groups emerged when a tornado struck Joplin, Mo., sweeping photos away from owners.

Two of those groups morphed into the Lost Photos of Joplin National Disaster Photo Rescue, run by the First National Baptist Church of Carthage, Mo.

Thad Beeler, director of National Disaster Photo Rescue and minister of music at the First Baptist Church, said that at the time there was no formal process to redistribute the more than 35,000 photographs that had been collected. But shortly after, an organized system to clean and file photos was developed and, perhaps more importantly, a proper way to distribute those photos back to their owners was implemented.

This isn't just a simple photo pass-off; it's a "reunification process" that connects a person to an old life. Each of the organization's 50-plus volunteers is trained in grief counseling and are taught how to help a person cope with what is often an overwhelming moment.

By: Judy Woodruff

I don't remember worrying about tornadoes as a little girl growing up in Oklahoma, but they were a real threat. In May 1950, the National Weather Service recorded an F-4 about an hour and a half south of Tulsa that killed five people and injured more than 30. I do remember hearing grown-ups talk about them, about how the Sooner State had the bad luck to attract them. My clearer memories are of endless summer days of 100-plus degree heat, when all we wanted to do was find shade and an ice cream cone.

By: Paul Solman

The relationship between unemployment and suicide is well established. But is the persistence of long-term unemployment an added factor in the rising suicide rate these days, especially for older workers? Paul Solman responds to a viewer's comment relating to this PBS NewsHour story, originally broadcast on May 3.

Paul Solman: Amidst a cascade of correspondence in reaction to our recent broadcast story on age discrimination and long-term unemployment, we received this email from "Karen" in Tennessee:

Why aren't people talking about age discrimination at a major level? I have been unemployed for more than five years. I have had training to add new skills to two degrees. Training and education mean nothing if no one will hire you. I live in a "right to work" state where corporations can do anything and government is in collusion in perpetrating this endemic discrimination ...

Companies aren't afraid of older workers -- they can and do anything they want. I have done everything a person can do to get a job and survive. I'm a woman alone and nobody cares. That's why the suicides have gone up drastically.

Karen's email, and particularly her last sentence, reminded me of a host of data, both old and new.

The U.S. ranks near the middle of the global suicide listings, according to the World Health Organization and consistently comes in around 10th when it comes to self-reported happiness, behind only the Scandinavian countries, Canada, Switzerland and Holland

But the suicide rate is rising in the United States, up by something like a sixth since the late '90s. (See the bottom half of Figure 1 on page six of the paper we linked to.)