NASA’s Goddard Institute for Space Studies (GISS) has published their data for global average temperature anomaly in June of this year. With June included, the latest data look like this:
It’s not really a surprise; global temperature continues to fluctuate, but those fluctuations are superimposed on a steady trend which, at present, is rising. If we compute yearly averages, we get this:
The final figure is 2018 year-to-date, which includes only the first half of the year. Still, 2018 is on track to be pretty hot, the 4th-hottest on record. Note that, using the year-to-date figure for 2018, the five hottest years on record are the last five years.
Much of the fluctuation is from causes unknown, but some of it is due to factors we do know about. Solar variations can increase or decrease the total energy arriving at Earth from space, although solar variations are only slight. Very large volcanic eruptions can throw junk into the upper atmosphere, and their sulfur compounds tend to end up as sulfate aerosols which scatter sunlight back to space and cool down the planet. One of the strongest and most pervasive fluctuation factors is the el Niño southern oscillation (ENSO); in its warm el Niño phase it heats up the atmosphere while in its opposite la Niña phase it cools us off.
Some climate deniers (are you there, “Global Warming Policy Foundation”?) still cling to the idea that the recent super-hot temperatures are just the result of the recent strong el Niño. Well, the el Niño is over — but temperatures remain above the previous decade’s average.
Still one wonders, how did ENSO affect recent temperatures? For that matter, how did those other known influences affect recent temperatures? To get some clues, I applied the method of Foster & Rahmstorf to estimate the impact of ENSO, volcanic eruptions, and solar variations on global temperature. Here’s the estimated impact of ENSO since 1975:
The strongest warming events due to ENSO were in 1983, 1998, and 2016. The strongest el Niño events were a bit before then, but there’s a lag between and el Niño event and its impact on global surface temperature. The effect of ENSO right now isn’t continued warming, it’s actually slight cooling.
The 1983 el Niño, strong as it was, was not followed by extra-high temperatures as were the 1998 and 2016 events. That’s because one of the other factors cancelled its warming influence, namely the cooling induced by the explosion of the el Chicon volcano. The estimated effect of all three fluctuating factors combined turns out to be this:
When we subtract the estimated impact of these fluctuation factors from observed temperature, we get an improved, “adjusted” temperature series — an estimate of how hot Earth would be without those factors that come and go but don’t last. It looks like this:
This makes the continued warming of the globe even more obvious … not that it wasn’t obvious already. We can, again, compute yearly averages:
This not only shows how global warming continues, it shows that when exogenous factors are removed, 2018 is on track to be the 2nd-hottest year, not 4th-hottest.
The adjusted series is helpful because it gives a better picture of what’s happening apart from known fluctuation factors. That gives a more precise estimate of the trend, and therefore of what we can expect in the near future.
As for what we can expect in the not-so-near future, that is best forecast based on physics, which is best computed with global climate models. They forecast a dire future … which is why climate deniers go to such lengths and sink to such depths of stupidity and dishonesty to insult them.
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