Weather Pushes World Temperature Over Threshold

  • Date: 09/11/15

From the bad news, suitably simplified, before the Paris Climate talks department comes a press release issued by the UK Met Office saying that the global annual average temperature for 2015 is set to exceed one degree C above pre-industrial levels. This means that we are halfway to the much-discussed hypothesis of the two degree C threshold for ‘dangerous’ climate change. But what is actually taking us into what the Met Office calls “uncharted territory” is inevitably a little more complicated.

It is widely accepted that the warmth observed in 2014 – 2015 and probably in 2016 is not due to a sudden increase in anthropogenic global warming but due to short-term natural effects such as the El Nino and the so-called “Pacific blob.” Without these natural effects (also known as weather) those years would be statistically indistinguishable from all the other years of the past fifteen years or so – instead of being a little above them. So it is misleading to say as Stephen Belcher, Director of the Met Office Hadley Centre, does: “We have seen a strong El Nino develop in the Tropical Pacific this year and that will have had some impact on this year’s global temperature.” ‘Some impact’ does not do it justice.

Likewise, “We’ve had similar natural events in the past, yet this is the first time we’re set to reach the 1 °C marker and it’s clear that it is human influence driving our modern climate into uncharted territory.”

Whilst it is true that we live in the warmest decade of the instrumental period, Belcher’s comment about human influence driving our climate into uncharted territory are interesting, even if they don’t tell the whole story.

According to the IPCC: “It is extremely likely [95 per cent confidence] more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together.”

Since about half of the annual average surface warming since 1850 occurred before 1952 this means that only about a quarter or a third of the overall warming has been anthropogenic.

Add to this the latest WHO figures on greenhouse gasses which states that, “between 1990 and 2014 there was a 36% increase in radiative forcing – the warming effect on our climate – because of long-lived greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from industrial, agricultural and domestic activities.”

Since there has been a 43 per cent increase in CO2 levels since the pre-industrial era this means that most of the additional CO2 forcing has occurred since 1990. The temperature rise in this period has been less than such a figure would imply. It is often suggested that this is because most of the heat has gone into the oceans. However, given the uncertainties in estimates of ocean heat content this has not been demonstrated unequivocally.

“Difficult to say”

What of the future? The Met Office says that, “Early indications suggest 2016 will be similarly warm and while it’s more difficult to say exactly what will happen in the years immediately after that, we expect warming to continue in the longer term.”

Expectation, especially when based upon a poor track record, is a poor guide.

To be more specific El Nino years are warmer than others but they are followed by cooler years, as was the case after the El Nino years of 2003, 2006, 2010 and it will probably be the case for 2015. See Figs 1 (Hadcrut4 data) and Fig 2 (GISS data). Typically La Nina years have sea surface temperatures about 1.5 °C lower with some regions being 3-5°c lower than El Nino years.

Hadcrut4 2015 so far

GISS

 

All things considered it’s likely that we will see a global cooling after the El Nino. The “hiatus” in global temperature has not gone away, it is being modulated by El Ninos. For those who see the “hiatus” as an inconvenient impediment to the forthcoming Paris talks, a sleight of hand with statistics and press releases, can be used to make it seem to go away.

Feedback: david.whitehouse@thegwpf.com



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