How much brain damage is too much? NFL players head for the exits.

The smartest player in the NFL just quit.

Not because he was unable to play, and certainly not because of his age–he's only 26. No, Baltimore Ravens' player John Urschel decided to quit because the risk of permanent, irreversible brain damage is just not worth it.

Urschel is a very smart guy. He's currently pursuing a Ph.D. in mathematics at MIT, one of the best and most demanding science universities in the world. Until this summer, he was (impressively) balancing his studies with being a full-time NFL player.

But when Dr. Ann McKee and colleagues published a new study showing that 110 out of 111 former NFL players had suffered serious brain damage, Urschel could no longer pretend he wasn't putting his future at grave risk. McKee's study, the largest study yet of chronic traumatic encephalopathy (CTE), showed alarmingly high rates of CTE in college and high school players as well (91% of former college players).

Let's get one point out of the way: everyone involved with the study, including Dr. McKee, knows that it was biased. The scientists examined brains of deceased players that had been donated to the study because family members–or the players themselves, before they died–suspected something was wrong. So perhaps the true risk of brain damage is lower than 99%. Maybe it's only 50%, or 20%. Do young men playing football want to take that risk?

John Urschel isn't the first player to quit because of the growing realization that football may cause irreversible brain damage. In 2015, San Francisco 49ers player Chris Borland retired at the age of 24, and in 2016 Kansas City Chiefs player Hussain Abdullah retired at 30, both over concerns about concussions and brain damage.

The NFL has been denying or downplaying the risk for years. A few years ago, after the suicide of former player Junior Seau, they announced a $30 million partnership with the NIH to study the risks of football on the brain. As results started coming in, showing that the risk was far more serious than most people knew, the NFL backed out of the deal with $16 million still unspent.

Meanwhile, the chorus of warnings has been growing steadily louder from the medical community. Last year, a former team doctor and a former football player and coach wrote in JAMA that

"unless there is a way to reduce the number of TBIs [traumatic brain injuries] caused by the sport, football will remain a threat to the brains and health futures of the players, including impaired cognitive function and reasoning, memory loss, emotional depression, and other sequelae that profoundly erode quality of life."

Earlier this year, a study out of the CDC reported that "3 high school or college football players die each year from traumatic brain and spinal cord injuries that occur on the field," most them as a result of being tackled during games.

Over the years, football players have grown ever larger (the average NFL lineman today weighs over 300 pounds) and the intensity of the violence on the field has grown with them. It's not just in the NFL, either: last year, three high school teams in the state of Washington forfeited their games against a local team out of a legitimate fear that players would be badly injured by the opposing team's 300-plus pound linemen. Their fears were justified: the human head simply wasn't built to withstand the repeated blows that players endure.

All players might do themselves a favor by listening to John Urschel. He explained his decision–and his abiding love for the game of football–in a lengthy interview on the Freakonomics podcast a couple of weeks ago. That interview should be required listening for young players, and even more so for parents who might be dreaming that their sons have a future career in football.

Houston, we have a problem. It's called global warming, whether you admit it or not.

Hurricane Harvey poured more rain on Texas and Louisiana last week than this country has ever seen from a single storm. The city of Houston is now suffering from historic flooding, with many calling this a "1000-year flood." Congress is likely to pass a huge bailout bill in the coming days, starting with a $14.5 billion "down payment," suggesting much more is to come.

The storm's eventual costs could rise even higher than the costs of 2005's Hurricane Katrina, which cost $160 billion according to NOAA.

Let's not dance around the issue: Hurricane Harvey was a direct consequence of global warming, which in turn is a direct consequence of human activities.

It's ironic that Texas (and Houston in particular) has an economy that is dominated by on oil and fossil fuels. Burning these fuels is what got us in this mess.

It's also ironic that Texas Senator Ted Cruz, who is now at the front of the line asking for a federal government rescue package, is a scientifically illiterate climate change denier. As I wrote shortly after he announced his candidacy for President in 2015, Cruz not only denied that global warming was happening, but he then went on to compare himself to Galileo, as if he were taking a brave and bold scientific position. Right.

A few facts: the Gulf of Mexico is 4 degrees warmer than normal this year, and it has been getting worse. Back in March of this year, the Washington Post's Jason Samenow reported that the Gulf was "freakishly warm, which could mean explosive springtime storms." Warm water feeds hurricanes, and Harvey feasted on it, sucking up energy and using it to dump ridiculous amounts of water onto south Texas.

Noted climate scientist Michael Mann, writing in The Guardian, took the slightly more nuanced position that "climate change made Hurricane Harvey more deadly." True enough: if you want to be strictly accurate, we can't prove that warming temperatures are the sole cause of Harvey. Maybe with cooler temperatures, we'd have had a hurricane anyway–but it would have been a far smaller one, and the damage would have been far less severe.

Mann also pointed out that global warming has already caused sea levels to rise over half a foot, which made the flooding in Houston significantly worse than it would have been otherwise.

Now it's time to rebuild, which raises a dilemma. The U.S. can't just abandon Houston, one of our country's largest cities, even if most of its residents deny the reality of global warming (and perhaps they don't). But given that global warming is well under way, with rising sea levels and warming oceans, more catastrophic flooding events like Harvey are highly likely. Should we pay to rebuild the city exactly as it was, basically ignoring the problems of floodwater management as Houston has done until now? Or should we use the government bailout funds to reduce the risk from future flooding?

Actually, it might do even more good to impose a simple requirement, before Texas gets any of our bailout funds. Let's require U.S. senators Ted Cruz and John Cornyn, and Texas governor Greg Abbot, to state publicly that global warming is real, that humans are making it worse, and that they will work in the future to mitigate the risks posed by continued climate change. Wouldn't that be something? A simple statement, nothing more, to unlock billions of dollars in aid.

If we just rebuild everything like before, then Houston will continue to have a problem.

(*Note about the title of this article. The original quote was "Houston, we've had a problem," famously utterly by Apollo 13 astronaut Jim Lovell. In the movie Apollo 13, actor Tom Hanks (playing Lovell) instead said, "Houston, we have a problem.")