National: On Thursday, two observatories in Hawaii confirmed that atmospheric carbon dioxide had exceeded 400 parts per million. When carbon dioxide levels were last this high, three million years ago, the world was 3 degrees hotter, the sea was at least 10 metres higher than today and camels roamed the high Arctic.
In itself, this is an arbitrary, but notable landmark in the steady rise of greenhouse gases. Before the Industrial Revolution, carbon dioxide was only 280 parts per million - since then global...