From Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming— green roofs are one of the 100 most substantive solutions to climate change.

From an aerial view, most cities are a patchwork of gray, brown and black rooftops. But look down over some parts of Stuttgart, Germany, or Linz, Austria, and many rooftops are easily mistaken for small parks or grassy squares. They are affirmation of the modern movement for Green or “living” roofs, which has taken off in the past 50 years. They also evoke a much longer history, back to the heyday of the Viking Age, when such roofs first became popular in Scandinavia. Rewind modern-day Norway to the ninth or 10th century, and you would find a landscape dotted with sod-roofed homes, now called torvtak.