Temperatures, as defined by “climate”, are based on temperatures over longer periods of time — typically 20-to-30-year averages — rather than single-year data points. But even when based on longer-term averages, the world has still warmed by around 1.3°C.3
But you’ll also notice, in the chart, that temperatures haven’t increased linearly. There are spikes and dips along the long-run trend.
Many of these short-term fluctuations are caused by “ENSO” — the El Niño-Southern Oscillation — a natural climate cycle caused by changes in wind patterns and sea surface temperatures in the Pacific Ocean.
While it’s caused by patterns in the Pacific Ocean and most strongly affects countries in the tropics, it also impacts global temperatures and climate.
There are two key phases of this cycle: the La Niña phase, which tends to cause cooler global temperatures, and the El Niño phase, which brings hotter conditions. The world cycles between El Niño and La Niña phases every two to seven years.4 There are also “neutral” periods between these phases where the world is not in either extreme.
The zig-zag trend of global temperatures becomes understandable when you are taking the phases of the ENSO cycles into account. In the chart below, we see the data on global temperatures5, but the line is now colored by the ENSO phase at that time.6
The El Niño (warm phase) is shown in orange and red, and the La Niña (cold phase) is shown in blue.
You can see that temperatures often reach a short-term peak during warm El Niño years before falling back slightly as the world moves into La Niña years, shown in blue.
What’s striking is that global temperatures during recent La Niña years were warmer than El Niño years just a few decades before. “Cold years” today are hotter than “hot years” not too long ago.7
Robin Edgar
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