Airbnb has pledged to provide free housing for 20,000 Afghan refugees, starting immediately. CEO Brian Chesky tweeted Tuesday: "The displacement and resettlement of Afghan refugees in the U.S. and elsewhere is one of the biggest humanitarian crises of our time. We feel a responsibility to step up." Chesky did not say how long refugees would be housed, or how long the company would fund their stays. U.S. officials say roughly 48,000 people have been evacuated from Afghanistan in recent days after the country's capital, Kabul, fell to the Taliban.