RACKPOT GLOBAL WARMING CLAIM OF THE WEEK: GLOBAL WARMING MEANS AIRPLANES WON'T TAKE OFF

The simplest answer: for an average-sized commercial jetliner with typical fuel and payload, the "takeoff speed" is around 130-160 knots, or about 150 to 200 miles per hour. The landing speed is more or less the same, usually a few knots slower. 

Introduction
Although density altitude is not a common subject for “hangar flying” discussions, pilots need to understand this
topic. Density altitude has a significant (and inescapable) influence on aircraft and engine performance, so every
pilot needs to thoroughly understand its effects. Hot, high, and humid weather conditions can cause a routine

takeoff or landing to become an accident in less time than it takes to tell about it.

Airplanes of the future will have to carry lighter loads more often thanks to global warming, according to two scientists at Columbia University, New York. They reached their conclusion by creating models which predicted that by 2060 there will be more warm days but no commensurate technological advances in the aviation industry.

The two scientists, Coffel and Horton, looked at a phenomenon known amongst pilots as ‘density altitude’, which affects a plane’s ability to take off. Essentially, on hotter days the air is less dense, making it harder to get a plane airborne. It is a particular problem at airports with short runways, as the planes will take longer to lift off.

Commercial aviation overcomes the problem by issuing weight restrictions at the airport on particularly hot days. Coffel and Horton sought to predict how many more weight restricted days there will be by 2050-2070, and decided, through use of models, that the "number of weight restriction days between May and September will increase by 50-200 percent at four major airports in the United States by 2050-2070," and that "these performance reductions may have a negative economic effect on the airline industry."

Their solution is for the aviation industry to start "planning for changes in extreme heat events" to "help the aviation industry to reduce its vulnerability to this aspect of climate change."

But as Anthony Watts of the blog Watt's Up With That points out: "Of course they are assuming that [their] models produce an accurate output, and that airplanes of the 2050-2070 era have the same airfoil efficiency and take-off power of today." Neither of which are by any means certain.