The New Normal

The answers I frequently get to the question “What is climate?” are commonly along the lines of “the average weather” or “climate is what we expect and weather is what we get.” Firstly, those are statistical statements, and secondly, an average is obviously dependent upon the time of the average. If it is a very “long-term” average to avoid interannual variability, then by definition there is no climate change. This conundrum was recognized back in the 1970s when it was proposed that we speak about “climate states.” This perhaps relates to what is now commonly known as a “base period.” The classic base period is a 30-year period (as defined by the World Meteorological Organization) that traditionally gets updated. Hence we went from the 1961–1990 normal to the 1971-2000 normal, and now 1981–2010 is the “New Normal.”