Saturday, 5 November 2016

A la-Nina developing as the world heats

There’s a La Nina Developing — So Why is the World Still Heating Up?


4 November, 2016
ong term, there’s no doubt what’s in control of the world’s temperature trend. The vast belching of greenhouse gasses by fossil fuel industry and related non-renewable based machinery has caused atmospheric carbon levels to hit 405 ppm CO2 and 490 ppm CO2e this year. All this added carbon has caused the world to warm by a record 1.22 C since 1880s levels during 2016 (approx). But superimposed over this long term warming trend is the natural variability based ebb and flow of atmospheric and surface ocean heat that is the ENSO cycle.
ENSO — A Wave Pattern Overlying the Long Term Warming Trend

Think of it as a smaller wave pattern that overlaps the current global upswing in temperatures. As El Nino builds and comes into the fore, natural forcings caused by periodic ocean surface warming in the Equatorial Pacific push global temperatures higher. This tends to add to the human forced global warming trend. So, often, El Nino years are also record warm years.
global-temperatures-enso
(El Nino to La Nina temperature variations create a wavy pattern in the overall global warming trend. Note — the record warm year of 2016 is not included in this graph. Image source: NOAA.)

Conversely, La Nina, which generates a periodic cooling in the Equatorial Pacific tends to pull a bit against the long term warming trend. So periods of La Nina tend to show average global atmospheric temperatures in the annual measure drop off by about 0.2 to 0.4 C from the peak periods of atmospheric heating during El Nino. Of course, since the ENSO variability typically follows a range of +0.2 C to -0.2 C but does not affect long term temperature trends, it only takes about a decade for La Nina years to be about as warm as recent El Nino years.
Slight Warming During Fall of 2016 Despite La Nina

During fall of 2015 and the winter and spring of 2016 a powerful El Nino helped to push global surface temperatures into new record high ranges. This happened because greenhouse gasses the world over had been loading heat into the Earth System for some time and the strong El Nino served as a kind of trip wire that opened the flood gates for a surge of atmospheric heat. Which is why 2016 will be about 1.22 C hotter than 1880s temperatures (1 C hotter than NASA 20th Century baseline temps) and why the years from 2011 to 2016 will average above 1 C hotter than 1880s values overall (0.8 C hotter than 20th Century baselines).
But now, with the 2016 El Nino in the rear view mirror and with a La Nina forming in the Pacific, we would expect global temperatures to cool down somewhat. For the most part, this has happened. Back in January and February, monthly average temperatures were as much as 1.5 C above 1880s averages. Since summer, the averages have dipped to around 1 to 1.1 C above 1880s values.
 
gfs_anomaly_timeseries_global
(Global temperatures bottomed out at around 1 C above 1880s or 0.4 C above the 1981 to 2010 average in this GFS based graph by Karsten Haustein during June then began to slowly climb through fall even as a weak La Nina developed.)

With La Nina continuing to form, we would expect these monthly values to continue to fall for a bit as La Nina strengthened. But that doesn’t appear to be happening. Instead, global atmospheric temperatures bottomed out at around 1 to 1.1 C above 1880s levels in June, July, August and September and now they appear to be rebounding.
Polar Amplification Signal Shows Up as a Blip in the Global Measure

In other words, we see a rise in the global temperature trend when we should see a steady counter-trend decline forced by natural variability.
Why is this happening?
The climate evidence points to a rather obvious set of suspects. For this fall saw extreme warming both in the northern and southern polar regions of the world. Today, temperature anomalies in both the Arctic and the Antarctic were 5.84 and 4.19 C above average respectively. A rough average between the two poles of +5 C for these high latitude regions. As we’ve mentioned many times before, such severe warming is an obvious signal of climate change based polar amplification where temperatures at the poles warm faster relative to the rest of the Earth during the first phase of greenhouse gas forced warming.
extreme-polar-amplification-november-4
(Extreme warming of the polar regions continued on November 4 of 2016. This warming is pushing against the La Nina trend which would tend to cool the world temporarily. Image source: Climate Reanalyzer.)

By themselves, these abnormally high temperatures at the poles would be odd enough. But when taking into account that La Nina should still be cooling the globe off, it starts to look like this severe polar warming has jostled the La Nina cooling signal a bit — turning it back toward warming by late fall. And if that is what’s really happening, then it would imply that the natural variability signal that is produced by ENSO is starting to be over-ridden by polar amplification based influences. In other words, there appears to be another signal that’s starting to intrude as a polar amplification based temperature spike.
It’s something that has popped up from time to time as a blip in the observational data over the past few years. But fall of 2016 provides one of the stronger signals so far. And it’s a signal related to a set of feedbacks that have the potential to affect the overall pace of planetary warming. Something to definitely keep an eye on.
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Hat tip to June


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