Cause of the Pause?

Posted on September 29, 2013
By Barry Brill

Background

The UN’s Intergovernmental Panel on Climate Change (IPCC) produces periodic reports on the science and policy relevant to dangerous anthropogenic global warming. These guide all UN members and the annual conferences of the parties which endlessly attempt to negotiate global binding treaties to reduce greenhouse gas emissions.

These technical reports run to thousands of pages and are barely comprehensible. A Summary for Policymakers (SPM) is constructed for the world’s media and politicians. The line-by-line wording of this document is negotiated ‘by consensus’ by bureaucrats representing the Environment Ministries of about a hundred member countries.

The SPM for the basic science Working Group (WG1) for the Fifth Assessment Report (5AR) was negotiated in Stockholm last week and released on Friday.

Recognising that even a 20-page SPM exceeds the attention span of most journalists, IPCC spin doctors distil the politically-relevant essence down to a single soundbite – a ‘meme’ which becomes the cultural motif of the entire report.

Here are the last three IPCC memes:

2001 TAR: “Most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”.

2007 4AR: “Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”

2013 5AR (leaked draft): “It is extremely likely that human influence on climate caused more than half of the observed increase in global average surface temperature from 1951 to 2010.”

 The ‘level of likelihood’ is a red herring. It has nothing to do with statistical probabilities and is purely a subjective assessment by a meeting of the lead authors. The step down from “most” to “more than half” is much more significant as the science community has been interpreting “most” as around 95% for the last 12 years.

The elephant in the room is that the metronomic ramping-up of asserted certainty takes no account of the global temperature standstill or “pause” which has dominated the data since the mid-1990s. The IPCC has relied on its CIMP5 array of computer models, without a hint of curiosity as to why they have been so wrong for so long.

Hans von Storch¹, an IPCC leader who has found there is only a 2% chance that the models are correct, offers five possible explanations:

(1) An underestimation of natural climate variability;

(2) The climate sensitivity of models may be too large;

(3) There is a missing component in the CMIP5 simulations (eg solar activity)

(4) The last 15 years may have been an outlier.

(5) Greenhouse gases play a minor or no noteworthy role in ongoing and expected future climate change.

Warmist von Storch dismisses (5) as being contrary to basic physics. His recent paper² finds that the likelihood of (4) is vanishingly small. (3) refers to natural forcings (solar and volcanic effects) which for our purposes can combine with natural variance in (1) as a ‘natural cause’.

So there are only two explanations: Either natural effects are much larger or human effects are much smaller than the IPCC has always estimated in the past.

Neither of these explanations appeal to the highly-politicised IPCC. The draft WG1 report tried to steer around them by hiding the pause in the eighth chapter and reducing the lower bound of climate sensitivity from 2°C to 1.5°C.

Environment bureaucrats were most unhappy with the efforts of the scientists in the first draft of the SPM and requested over 1800 amendments. They split between those who demanded that the pause/standstill be tackled head-on to those (like Germany and Hungary) who wanted it to be totally ignored.

Those countries (like the USA) arguing for disclosure said that skeptics would have a field day with the pause/standstill if the issue is not nailed. But it is not only the skeptics:

• Since January 2012, there have been 19 journal papers on climate sensitivity, all of which found that the IPCC estimate of 3°C is grossly overstated;
• Since the IPCC cut-off date in February 2013, the leading warmist-leaning journal, Nature Climate Change, has published a string of papers which offer conflicting reasons for the pause;
• Three leading IPCC figures have co-authored a paper showing that IPCC models have overstated warming by 100% over the last 20 years and by 400% over the last 15 years;
• Other IPCC lead authors have argued that the 21st century pause is driven by the Pacific Decadal Oscillation (PDO) which lessens El Ninos and flipped to negative in about 2003. (They don’t spell out the obvious corollary that the 1990s warming was also due to the PDO).

Some commentators believe a consensus is forming around a contention that the “missing heat” is hiding in the depths of the ocean. This hypothesis, pushed by New Zealander Kevin Trenberth, is that dangerous anthropogenic global warming has continued over the last 15 years but has switched from the atmosphere to the deep hydrosphere. We all need more science funding to find out why.

The “ocean ate my warming” theme has lots of problems. For one thing, it tends to put the kibosh on any international treaty while this wholly new climate theory is explored and its dangers quantified. What is “the social cost of carbon” while the pause drags on?

Outcomes

A committee of over 100 bureaucrats pulling two successive all-nighters in Stockholm produced a report which is barely readable. A masterpiece of obscurantism, all the “ducking and diving, bobbing and weaving” has left the central meme intact – i.e. humans caused “more than half” of the warming (land and oceans) since 1951.

The contretemps over treatment of “the pause” seems to have been won by the deniers. The scientists were directed to remove a key sentence which has been sitting in their draft since June:

“Models do not generally reproduce the observed reduction in surface warming trend over the last 10–15 years.”

The “observed reduction” term is apparently persona non grata, as are words like “pause” or “hiatus” or “standstill”.

This has led Professor Judith Curry to comment… “the IPCC has thrown down the gauntlet – if the pause continues beyond 15 years (well it already has), they are toast”. The Global Warming Policy Foundation says the IPCC “is very likely going to suffer an existential blow to its credibility”.

But the pause was still officially recognised. As The Economist reports:

“The IPCC admits the pause in the rise of surface air temperatures is real. “The rate of warming over the past 15 years,” it says, “[is] 0.05ºC per decade…smaller than the rate calculated since 1951.” In its 2007 report the panel had said the rate of warming was 0.2ºC per decade in 1990-2005 (four times the current rate). It predicted that this would continue for the next two decades”.

The report says the slowdown in observed warming could be due to natural variability and ‘over-sensitive responses’ to greenhouse gases in some climate models.

The most important issue addressed by the SPM was a complete damp squib. The perennial climate debate is about the SCALE or danger of anthropogenic global warming, not its existence. As Gareth Morgan puts it in his book “Poles Apart” the difference between alarmists and sceptics is that the former say climate sensitivity is 3°C while the latter say it is 1°C. “Sensitivity” is the temperature increase caused by a doubling of atmospheric CO2.

Ever since a 1979 committee (see http://en.wikipedia.org/wiki/Climate_sensitivity) guessed sensitivity at 3°C, climate models have been driven by this figure. All four previous IPCC reports have confidently asserted a ‘best estimate’ of equilibrium climate sensitivity at 3°C. But this year they have faltered:

“No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies.”

So much for 95% certainty! Or the canard that there is a 97% consensus amongst climate scientists.

Perhaps the most telling figure in the report is that the range of sensitivities has been lowered. The new lower bound of 1.5°C would mean that warming in the 21st century will be about the same as the 20th century. Nobody is going to be very alarmed about that!

The observed warming trend over 1951-2010 was just under 0.12°C/decade, with natural contributions being in a range of -0.2 to 0.2°C. There was no evidence whatever for the “more than half” (0.06°C) attributed to human activity, the allocation being based solely on “expert judgment”.

And the prediction section has some good news from the models:

Temperature change for the end of the 21st century is likely to exceed 1.5°C relative to 1850-1900 for all RCP scenarios except RCP2.6. It is likely to exceed 2°C for RCP6.0 and RCP8.5, and more likely than not to exceed 2°C for RCP4.5 ³.

Global mean sea level rise for 2081−2100 relative to 1986–2005 will likely be in the ranges of 0.26 to 0.55 m for RCP2.6, 0.32 to 0.63 m for RCP4.5, 0.33 to 0.63 m for RCP6.0, and 0.45 to 0.82 m for RCP8.5 (medium confidence).

Economic models (17 have been published) show that the net effects of warming are expected to be beneficial until the threshhold of 2°C is passed. The SPM suggests that outcome is most unlikely during the 21st century.

Sea level rise is much the same as it has been during the past 14 centuries. The ‘global average sea level’ rises more slowly than toenails grow and no acceleration⁴ is in evidence.

Highlights of the SPM:

• There is no longer any IPCC consensus on the best estimate of climate sensitivity.
• The range of values for climate sensitivity is lowered.
• The 16-year temperature standstill or “pause” is officially recognised (if reluctantly).
• The anthropogenic share of past warming is reduced from “most” to “more than half”.
• Warming for the next hundred years will likely be similar to the last 100 years.
• Temperatures through to 2100 are expected to remain below the 2°C threshold.
• Sea level rise this century is predicted to be non-threatening.