Police in riot gear raided Columbia University in New York City last night, arresting dozens of pro-Palestinian protesters encamped in a university building. Columbia President Minouche Shafik said she had "no choice" but to call in the New York Police Department to remove the protesters, exactly 56 years to the day after the same police department "violently cleared" a 1968 student occupation of the university, said The New York Times. The demonstration and arrests "aren't new ground" at the university, said The Associated Press. They're the latest in "a Columbia tradition" dating back more than five decades. 

1968 Vietnam War and civil rights protest 
On April 23, 1968, Columbia students began protesting at the U.S.'s role in the Vietnam War and "university policies they considered racist," said The Washington Post. They demanded an end to the university's affiliation with a think tank involved in Pentagon weapons research. They also wanted to halt plans for a segregated gym in a nearby park that was thought to have separate entrances for Columbia students and Harlem residents. 

On April 30, at the behest of Columbia's president, about 1,000 New York City police officers "poured onto the campus" to clear out the demonstrators. Students were "punched with brass knuckles, kicked, dragged down concrete steps, thrown to the ground and then stomped upon by the police," student publication Barnard Magazine reported at the time. But by another metric, the protests were successful. Columbia disaffiliated from the weapons think tank, the Institute for Defense Analyses, and scrapped the plans for the gym. 

1985 anti-apartheid protests 
In April 1985, 100 to 200 students blockaded Hamilton Hall for three weeks, demanding that the university divest from corporations profiting from apartheid in South Africa, said Al Jazeera. The protests ended on April 25 with a march into Harlem and eventually led to the "first successful divestiture campaign" at Columbia, with the university agreeing to divest itself of the remainder of its investments with South African connections. In 1986, the government also "bowed to pressure," said Vox, and enacted a divestment policy.

For nearly a decade, Costa Rica has generated 99% of its electricity from renewable sources of energy. For comparison, the U.S. manages slightly more than 20%, said The Verge. Most of the Central American nation's electricity, about 73%, is generated by hydropower thanks to its heavy rainfall, tropical location and natural topography. It also boasts a high concentration of rivers and dams, as well as a small population and no major industry. 

A 1949 law that established the state-run electricity utility Instituto Costarricense de Electricidad (ICE) said Costa Rica should develop its natural resources for its electricity supply, and at the time, hydropower was the only source available. Having one state energy company rather than smaller private electric utilities also helps simplify the planning process. 

But even Costa Rica's consistent 99% is not a "perfect system," said The Verge. When the El Niño weather pattern brought higher temperatures and lower rainfall last year, it gave an inkling of the future impact of climate change. The hydropower reservoirs suffered a 16% reduction, while demand for electricity rose as people used more air-conditioning. 

"In the rainy season, our reservoirs normally recover," said Kenneth Lobo Méndez, the director of planning and sustainability in electricity management. They were "extremely low" last year, so this year's dry season could be "a little bit complicated." 

In the south of the country, rainfall is forecast to increase due to climate change, but "we can't get that rainfall into our system," said Marco Jiménez Chavez, a generation expansion engineer for ICE. Hydroelectric plants in that region are "not ready to harness that amount of waterfall."