Why is Texas experiencing a winter freeze?
TEXANS ARE not used to putting on snow boots and salopettes. Temperatures in much of the state rarely drop below 5C during the winter. This weeks extreme chill, which has brought snow storms and sent thermometers down to -18C in places, has thrown Texas into chaos. Power outages, caused by a combination of high demand, power plants crippled by the weather and a grid that is cut off from the rest of the country, have left millions of people shivering in the dark (see article). President Joe Biden has declared a state of emergency. For the first time, winter-storm warnings are in place in all 254 counties, home to almost 29m people. What explains the deep freeze? Texans current chill was caused by rapid heating in the stratosphere, the second-lowest section of the atmosphere, 8-50km (5-30 miles) above the Arctic. Known as sudden stratospheric warming, it causes the polar vortexa ring of cold air that encircles the polesto weaken, lessening the forces that keep cold air corralled at high latitudes. This increases the movement of cold air southward and warm air northward, allowing low temperatures to sweep into typically warm areas such as the southern United States. (This phenomenon works both ways. Britain, for example, will probably be blasted with unseasonably warm air from Morocco in the coming weeks.) Some scientists are keen to link such cold snaps to climate change, arguing that warming temperatures in the Arctics troposphere (the lower atmospheric level which begins at the surface) are weakening the polar vortex and allowing bitter air to escape from the north more often. Climate change, driven by emissions from fossil fuels, is undeniably causing temperatures in the Arctic to increase at unprecedented rates, and far faster than elsewhere on the planet. But as yet, no clear causal link has been proven between climate change and the behaviour of the polar vortex. In the winter of 2019-20, for example, the vortex was exceptionally strong (because of a cool stratosphere), despite continued signs of global warming at the Arctics surface. Geert Jan van Oldenborgh, of the Royal Netherlands Meteorological Institute, points out that data show that climate change is making cold snaps in mid-latitude regions rarer and less frigid than they once were, regardless of their cause. For now, Texan politicians are scrambling to restore power and make roads safe to travel on. There is plenty more they can do in the future. Wind turbines, power plants and power lines can be cold-proofed, but it is cheaper not to, and utility companies in Texas are not required to do so (unlike those in northern states). The grid would also benefit from more capacity to deal with spikes in demand. This could come from cold snaps, or hotter summers. (Air-conditioning use stretched Texass grid almost to breaking point in the summer of 2019.) And vulnerable residents such as the old, the poor and the homeless, who are suffering particularly severely in the current freeze, need proper shelter and food supplies. Climate change may not explain the weather this time. But better preparation will also help during droughts, wildfires and severe hurricanes, all of which are becoming more common.