Record CO2 Levels Reported As Global Warming Pause Reaches 19 Years

The long term remorseless rise in atmospheric CO2. This has been rising consistently throughout the whole period of the global warming pause rasing questions about the nature of the link between CO2 and climate change. Courtesy: NOAA and the Scripps Institution of Oceanography

The long term remorseless rise in atmospheric CO2. This has been rising consistently throughout the whole period of the global warming pause raising questions about the nature of the link between CO2 and climate change. Courtesy: NOAA and the Scripps Institution of Oceanography.

Today the World Meteorological Organization (WMO) confirmed that in 2013 the atmospheric concentration of carbon dioxide (CO2)  and other so called greenhouse warming gases rose at the fastest rate since 1984.

Greenhouse gas concentrations in the atmosphere, including CO2, methane and nitrous oxide, reached record levels in 2013. WMO Secretary General Michel Jarraud warned that we are “running out of time” to curb the rise in atmospheric CO2. This came as UK Energy And Climate Change Secretary Ed Davey called for an “ambitious agreement” among the world’s governments next year to cut global CO2 emissions.

There is no doubt that the levels of CO2 and other greenhouse gases in the atmosphere have been growing. Indeed, there is now nearly one and a half times more CO2 in the atmosphere than there was at the start of the industrial revolution. There is also no doubt that these gases help keep the planet warm – and that putting more of them into the atmosphere will make our planet warmer. The warming effect of greenhouse gases has increased by a third since 1990 and most of this additional warming effect is due to CO2, according to the WMO.

The trouble is that for most of the time since 1990 global temperatures have remained flat, albeit at a high level. This raises awkward questions about the nature of the link between global warming and rising atmospheric CO2 concentrations. And just as the remorseless increase in CO2 is a rock solid scientific fact, recorded by measurement instruments around the world, so there can be little doubt about the hiatus in the rise of global surface temperatures – the pause.

Pause problem

This pause in global warming can be seen in all the main temperature data sets maintained by the likes of US space agency NASA and the UK Meteorological Office. True, there has been some debate about when the pause started and it depends on which of the various temperature records is considered. An analysis published last week shows that there has been no statistically significant warming in global surface temperatures recorded by the Met Office since 1995; and in the case of satellite data collected by US firm Remote Sensing Systems, the pause appears to have lasted for 26 years.

A statistical analysis of global temperature data indicates that the so called pause or hiatus in global warming dates back to 1995 – 19 years ago. The existence of the pause in global warming was acknowledged by the Intergovernmental Panel on Climate Change last year but there has been significant debate about the actual duration of this hiatus with some commentators alleging that the length is exaggerated by cherry-picking the start date as 1998 – a particularly warm year. Ross McKitrick from the Department of Economics at the University of Guelph in Canada believes his statistical analysis used in the paper published in the Open Journal of Statistics avoids the potential biases and is immune to the charge of cherry-picking. In the conclusion to the paper McKitrick, an acknowledged climate sceptic, writes: “In the surface data we compute a hiatus length of 19 years”. This graphic from the paper shows the trend in temperatures in the UK Met Office HadCRUT 4 data set and illustrates that a flat trend can be dated back to 1995. Trend magnitudes  are black dots and the 95% robust confidence intervals are solid lines. Image courtesy of OJS and Ross McKitrick.

A statistical analysis of global temperature data indicates that the so called pause or hiatus in global warming dates back to 1995 – 19 years ago. The existence of the pause in global warming was acknowledged by the Intergovernmental Panel on Climate Change last year but there has been significant debate about the actual duration of this hiatus with some commentators alleging that the length is exaggerated by cherry-picking the start date as 1998 – a particularly warm year. Ross McKitrick from the Department of Economics at the University of Guelph in Canada believes his statistical analysis used in the paper published in the Open Journal of Statistics avoids the potential biases and is immune to the charge of cherry-picking. In the conclusion to the paper McKitrick, an acknowledged climate sceptic, writes: “In the surface data we compute a hiatus length of 19 years”. This graphic from the paper shows the trend in temperatures in the UK Met Office HadCRUT 4 data set and illustrates that a flat trend can be dated back to 1995. Trend magnitudes are black dots and the 95% robust confidence intervals are solid lines. Image courtesy of OJS and Ross McKitrick.

This is a tricky problem. For the duration of the pause is now approaching the length of the period of rapid warming that triggered fears over global warming in the first place. In simple terms, global temperatures were fairly flat through out the 1950s and 1960s until around 1975, then they rose rapidly for around two decades until the mid 1990s when they leveled off and the pause began.

It is trickier still in that scientists can not agree on the cause of the pause. Possible explanations include a build up of heat in the deep oceans, a weakening of solar activity and aerosols of volcanic ash in the atmosphere reflecting the sun’s rays back into space. However, the impact of solar activity and volcanoes does not appear sufficient to explain the problem and the accumulation of deep ocean heat appears to be somewhat elusive – the measured increase in ocean heat content being less than that required to explain the pause.

Furthermore, the computer climate models used by the Intergovernmental Panel on Climate Change (IPCC), have not predicted the pause and so they over-estimated the amount of warming that had been expected over the last decade. This fact has been seized on by climate sceptics as evidence that climate models do not work and therefore that the IPCC’s projections for future warming – the key reason cited by scientists and politicians for curbing global CO2 emissions – are inherently unreliable.

New research

Two interesting papers have appeared in the last month, published in the prestigious journal Nature Climate Change, which shed some light on the subject. One shows that climate models can replicate a pause similar to what we have seen if they assume that the surface waters of the Pacific Ocean are in the cooling phase of one of their long-term 15-20 year warming and cooling cycles; the implication being that global warming will kick-in again when the cycle flips back to warming. The other paper suggests that natural variations in the climate linked to the these same long-term cycles in the Pacific Ocean have indeed added to the warming seen in the 1980s and, equally, depressed global surface air temperatures in the last decade or so.

This paper suggests that half (47 per cent) of the warming seen in the 1980s was due to these natural cycles. If the natural cycles are about the same scale as the underlying global warming trend then they would tend to double the impact of man-made global warming in what is called their positive phases and more or less off-set it in their negative phases – producing a pattern of rapid warming followed by stalls. The clear implication of this – which is not spelled out in the paper – is that the link between CO2 and global warming is weaker than the IPCC has been suggesting; perhaps only half as strong as has been programmed into the IPCC’s computer models.

Now none of this means that climate change is not real, that global warming is not happening, that CO2 is not a warming gas or that CO2 levels are not increasing. But it does have important implications for policy makes. For it would make a huge difference to the projections for future temperature rises – and to our chances of avoiding a potentially catastrophic 2oC rise if the rate of warming were only about half of what had been forecast. It could tilt the policy balance between adaptation and mitigation in favour of adaptation.

All this appears in the run up to a major international conference in Paris next year that, if British minister Ed Davey gets his way, could saddle the world – and especially the industrialised economies of the West – with hugely costly and potentially unnecessary carbon reduction targets.

Whatever Davey and fellow politicians may believe, and state in their speeches, the science is far from “settled” – as the latest research shows.

Perhaps our politicians should actually read some of these scientific papers before they go to Paris.

Sources

WMO

WMO annual Greenhouse Gas Bulletin here.

WMO press release with jarraud quote here.

Ed Davey

UK Energy and Climate Change Secretary Ed Davey’s speech here.

Pause statistics paper

HAC-Robust Measurement of the Duration of a Trendless Subsample in a Global Climate Time Series by Ross R. McKitrick published in Open Journal of Statistics Volume 4, Number 7, August 2014 (Special Issue on Robust Statistics) DOI: 10.4236/ojs.2014.47050  here.

There’s a news story about this paper here.

Climate model paper

Climate model simulations of the observed early-2000s hiatus of global warmingby Gerald A. Meehl, Haiyan Teng and Julie M. Arblaster published in Nature Climate Change. DOI: 10.1038/NCLIMATE2357 here.

There’s a news story about this paper here.

Natural variations paper

Contribution of natural decadal variability to global warming acceleration and hiatus by Masahiro Watanabe, Hideo Shiogama, Hiroaki Tatebe, Michiya Hayashi, Masayoshi Ishii & Masahide Kimoto published in Nature Climate Change (2014) doi:10.1038/nclimate2355 here.

There’s a news story about this paper here.

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