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Another warm El Nino year

Dr David Whitehouse, GWPF Science Editor

2020 is gearing up to be another warm year, strongly affected by natural and regional weather events

It’s that time of the year again when some meteorological organisations predict what the average global temperature might be for the full, current year. Not that we have all the data for 2020, obviously, for most global temperature datasets haven’t even processed November’s data yet. Making a prediction with only just over 80% of the data available is a risky procedure and most sensible scientists would be very circumspect about doing so. But these premature annual announcements are done for political purposes and, in a typical year, always as a precursor to a UN climate conference.

2020 has been a warm year, one of the warmest – and warm years make many people throw caution to the wind, making claims based on select facts they like, ignoring the ones they don’t like.

Let’s go back a few years to the early part of this decade when global temperature had been stagnating for more than ten years and not increasing significantly, as many had predicted. But then came 2014-15 when they started rising again, peaking in 2016. Many voices proclaimed that this was evidence that global temperatures were now accelerating ‘out of control’, something their models had been predicting all along. The climate was making up for all the unchanging years of the so-called global warming hiatus, it was claimed.

Never mind that the sudden rise between 2015 and 2016 was occurring much faster than could be due to greenhouse forcing alone.

2010 – 2020: HadCrut4 global surface temperature change (green); Oceanic Niño Index (ONI) (red/blues)

However, it was not a coincidence that 2016 experienced a record El Nino. For some commentators, however, an El Nino is a finite event. According to its definition – a specific temperature increase in a certain region of the Pacific – an El Nino is either on or off. Hence, they said that subsequent warm years after 2016 were warm due to greenhouse forcing, not El Nino. They argued that average global temperature since then was not influenced by any El Nino warming.

But that’s clearly not the case. The build-up in temperatures before recent El Ninos is obviously not independent of its peak and neither is the decline afterwards, else why did that increase not continue after the El Nino’s ‘interruption.’ So, a year can still be showing the warming influence of previous El Nino conditions whilst not having an El Nino event, something many journalists and even the General Secretary of the World Meteorological Organisation (WMO), Prof Taalas, prefer to ignore.

Record warm years have usually coincided with a strong El Niño event, as was the case in 2016. We are now experiencing a La Niña, which has a cooling effect on global temperatures, but has not been sufficient to put a brake on this year’s heat. Despite the current La Niña conditions, this year has already shown near record heat comparable to the previous record of 2016,” said Prof. Taalas. 

Now take a look at global temperatures of 2020 and the past decade in general.

Looking at the monthly and quarterly data shows that quite a number of months earlier this year were affected by El Nino conditions, very different from what Prof. Taalas insinuated.

For reference here are the El Nino/La Nina years. Cold & warm episodes by season; NOAA Climate Prediction Center

Another point to consider is the distortion caused by averaging regional temperature events to draw a global picture. The BBC said that the most notable warmth this year was recorded in the Siberian Arctic, where average temperatures were 5C above average. Indeed, if you look at the graph accompanying the WMO’s press release you will immediately see that most of the warm temperature anomalies this year occurred in the Siberian Arctic – while the rest of the world has seen comparatively little change from previous years.

Global map of temperature anomalies relative to the 1981-2010 long-term average from the ERA5 reanalysis for January to October 2020. Graphic: Copernicus Climate Change Service / ECMWF

This means we will have to wait several more years before being able to assess global temperature trends outside significant natural weather events. But this won’t be easy because we are currently witnessing the start of a La Nina – the opposite of El Nino – and thus the prospect of temperature stagnating or even a drop in temperatures. A strong La Nina, such as the one in 2007, could numerically depress years of global warming.

The conclusion is that whenever climate scientists or journalists talk about a very warm year that is evidently influenced by El Nino warming it is not so much about global warming, but more about significant natural as well as regional weather events that are making a big difference.