Andrew Grant:

In a billion years the sun will unleash 10 percent more energy than it does now, inducing an irrefutable case of global warming here on Earth. The oceans will boil away and the atmosphere will dry out as water vapor leaks into space, and temperatures will soar past 700 degrees Fahrenheit, all of which will transform our planet into a Venusian hell-scape choked with thick clouds of sulfur and carbon dioxide. Bacteria might temporarily persist in tiny pockets of liquid water deep beneath the surface, but humanity's run in these parts would be over.

If the human population can successfully colonize planets orbiting Proxima Centauri or another red dwarf, we can enjoy trillions of years of calamity-free living. Says University of California, Santa Cruz, astronomer Greg Laughlin, "The future lies with red dwarfs."

That is, until the red dwarfs die.

Michael Specter:

One cubic mile of oil would fill a pool that was a mile long, a mile wide, and a mile deep. Today, it takes three cubic miles' worth of fossil fuels to power the world for a year. That's a trillion gallons of gas. To replace just one of those cubic miles with a source of energy that will not add carbon dioxide to the atmosphere--nuclear power, for instance--would require the construction of a new atomic plant every week for fifty years; to switch to wind power would mean erecting thousands of windmills each month. It is hard to conceive of a way to replace that much energy with less dramatic alternatives. It is also impossible to talk seriously about climate change without talking about economic development. Climate experts have argued that we ought to stop emitting greenhouse gases within fifty years, but by then the demand for energy could easily be three times what it is today: nine cubic miles of oil.

Brad Plumer on the work of Marc G. Millis, a former NASA expert on breakthrough propulsion:

We probably won't be ready to travel to other stars for at least another two to five centuries. Even if we do invent faster, niftier spaceships, there may not be enough energy available to reach other stars anytime soon.

No matter when we launch the first interstellar probe, it'll take a long time to reach its destination. Which means it's quite plausible that we'll later invent a newer, faster interstellar probe that gets to the star even sooner, with more modern equipment. Which raises the question of why we even bothered to launch that first probe.

Abdul Nasir:

I've worked with the Afghan Army. They get tired making TV commercials!