Searching for Real Global Temperature Trend amidst storm of climate records, part 1 – Likelihood: “99.9999%” there IS a trend

It’s 2016 now and 2016 is becoming a whole different story than 2015, that in turn was a whole different story than 2014. But still, also heat-record-breaking 2014 remains an interesting case – as that year broke the then-proclaimed temperature plateau (which of course was never there) – and because 2014 was not an El Niño year (although it was developing in deeper waters), but an ENSO neutral year.

As it currently rains climate records – we become increasingly interested to find out where the actual temperature trend lies, and especially if perhaps it might be higher than we previously thought, and current records are no mere ‘peaks on the graph’, but in fact climatic catch-up manoevres, placing global climatic warming in an even higher gear – and if so, further deteriorating climatic projections for the rest of this century.

No. It’s not that we like bad news. We like facts – and everything that comes close. A little order in the chaos. And that in our view means you need to read established scientific journals while you skip breakfast. Today it’s Nature – and an interesting new study by Michael Mann, Stefan Rahmstorf and other climatologists, that was published on 24 January:

Observed and modelled global temperature rise - records right on trend
When you insert ‘anthropogenic greenhouse gas forcing’ into the latest edition of the ‘Coupled Model Intercomparison Project’ (CMIP5) – that runs some 30 global coupled ocean-atmosphere general circulation models (in other words, the best that science has to offer) – you get the black line in the above graph – a line that comes very close to drawing a trendline for both observed northern hemisphere land & ocean warming (left graph, red line) and observed global land & ocean warming (right graph, red line). Temperatures shown as deviation from 1880-2014 climatic average – image from mentioned Nature study.

This study, called ‘The Likelihood of Recent Record Warmth’ looked back at the first of the new series of surpassing ‘hottest years on record’ – the year 2014. It concluded this record-setting event was ‘likely’ to occur, as a cause of the anthropogenic rise in greenhouse gas concentrations, better known as ‘man-made climate change’.

In the absense of this global climate forcer – represented in the graph below – the heat records would not be part of a trend (there is of course always a trend – but it would be flat).

graph natural climate variability + model runs with and without anthropogenic warming
Graph shows trend of natural climate variability (blue line), ensemble model runs creating ‘random yet plausible’ climate noise (Monte Carlo method – grey line) and again the CIMP5 computation for the anthropogenic climate warming trend – the one that follows observed temperature rise.

The measured global average temperature for 2014 would have been bizarrely unlikely to have occurred in that case – a chance of 1 in a million – the Nature authors write.

The difference between ‘ENSO neutral’ – and the Real Temperature Trend

We think that is a good first step in our quest to find the trend. At the end of 2014 the top three hottest years were (3) 2005, (2) 2010 and (1) 2014. These records are ‘likely’ under modelled climate change – and therefore offer an indication of where the upward trend lies.

But what about more recent climatological events? Currently world average temperatures are clearly picking up. The year 2015 broke the record of 2014 by a large margin – and 2016 is forecast to become hotter still.

Part of this is El Niño, but as we discussed two days ago – the latest records are (to a large extent) not caused by El Niño – but perhaps by climate feedbacks. We want to be better able to explain these temperature records and especially try to better understand where the actual global temperature trend lies. This is not an easy subject, so it will probably be a new series of articles.

Next up: aerosol cooling. You can draw a trend between La Niña and El Niño events and have a nice-looking graph. But it wouldn’t tell you the full story if you ignore another possible trend-masking factor.

© Rolf Schuttenhelm |

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