Much of the Alps just aren’t what they usually are this time of year: Sparse snowfall and unseasonably warm weather in much of Europe is allowing green grass to blanket mountaintops across the region where snow might normally be, causing headaches for ski slope operators and aficionados of Alpine white this time of year.Patches of grass, rock and dirt were visible Monday in place of what would normally be a blanket of white this time of year in some of Europe’s skiing meccas — places like Innsbruck in Austria, Villars-sur-Ollon and Crans-Montana in Switzerland, and Germany’s Lenggries and far beyond. It has revived concerns about temperature upheaval linked to climate change.On a swath stretching from France to Poland, but with the Alps at the center, many parts of Europe were enjoying short-sleeve weather. A weather map showed Poland racking up daily highs in the double digits Celsius — or more than 50 Fahrenheit — in recent days.It’s a sharp contrast to the frigid weather and blizzards in parts of the United States late last year.