Guest essay by Eric Worrall

In the wake of the science committee testimony, Climate Scientist Keven Trenberth has insisted that Climate Science does follow the scientific method. But Trenberth himself may have strayed outside accepted scientific methodology.

Yes, we can do ‘sound’ climate science even though it’s projecting the future

Nobody can observe events in the future so to study climate change, scientists build detailed models and use powerful supercomputers to simulate conditions, such as the global water vapor levels seen here, and to understand how rising greenhouse gas levels will change Earth’s systems. NCAR/UCAR, CC BY-NC-ND

April 6, 2017 4.01am AEST

Authors

Kevin Trenberth
Distinguished Senior Scientist, National Center for Atmospheric Research

Reto Knutti
Professor, Eidgenössische Technische Hochschule (ETH) Zürich

Increasingly in the current U.S. administration and Congress, questions have been raised about the use of proper scientific methods and accusations have been made about using flawed approaches.

This is especially the case with regard to climate science, as evidenced by the hearing of the House Committee on Science, Space and Technology, chaired by Lamar Smith, on March 29, 2017.

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Chairman Smith accused climate scientists of straying “outside the principles of the scientific method.” Smith repeated his oft-stated assertion that scientific method hinges on “reproducibility,” which he defined as “a repeated validation of the results.” He also asserted that the demands of scientific verification altogether preclude long-range prediction, saying, “Alarmist predictions amount to nothing more than wild guesses. The ability to predict far into the future is impossible. Anyone stating what the climate will be in 500 years or even at the end of the century is not credible.”

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Why climate scientists use models

The wonderful thing about science is that it is not simply a matter of opinion but that it is based upon evidence and physical principles, often pulled together in some form of “model.”

In the case of climate science, there is a great deal of data because of the millions of daily observations made mostly for the purposes of weather forecasting. Climate scientists assemble all of the observations, including those made from satellites. They often make adjustments to accommodate known deficiencies and discontinuities, such as those arising from shifts in locations of observing stations or changes in instrumentation, and then analyze the data in various ways.

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Projections, not predictions

With climate models as tools, we can carry out “what-if” experiments. What if the carbon dioxide in the atmosphere had not increased due to human activities? What if we keep burning fossil fuels and putting more CO2 into the atmosphere? If the climate changes as projected, then what would the impacts be on agriculture and society? If those things happened, then what strategies might there be for coping with the changes?

These are all very legitimate questions for scientists to ask and address. The first set involves the physical climate system. The others involve biological and ecological scientists, and social scientists, and they may involve economists, as happens in a full Intergovernmental Panel on Climate Change (IPCC) assessment. All of this work is published and subject to peer review – that is, evaluation by other scientists in the field.

The question here is whether our models are similar enough in relevant ways to the real world that we can learn from the models and draw conclusions about the real world. The job of scientists is to find out where this is the case and where it isn’t, and to quantify the uncertainties. For that reason, statements about future climate in IPCC always have a likelihood attached, and numbers have uncertainty ranges.

The models are not perfect and involve approximations. But because of their complexity and sophistication, they are so much better than any “back-of-the envelope” guesses, and the shortcomings and limitations are known.

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Read more: http://ift.tt/2pbhtqd

Trenberth has a lot of faith in his models – so much so, a few years ago he demanded that the “null hypothesis” be reversed. If accepted, this would have meant a reversal of the burden of proof regarding the assumption of human influence on global climate.

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“Humans are changing our climate. There is no doubt whatsoever,” said Trenberth. “Questions remain as to the extent of our collective contribution, but it is clear that the effects are not small and have emerged from the noise of natural variability. So why does the science community continue to do attribution studies and assume that humans have no influence as a null hypothesis?”

To show precedent for his position Trenberth cites the 2007 report by the Intergovernmental Panel on Climate Change which states that global warming is “unequivocal”, and is “very likely” due to human activities.

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Read more: http://ift.tt/2p9YD3x

Trenberth’s demands for a reversal of the burden of proof with regard to climate were rejected by the scientific community. Even climate advocate Myles Allen, head of University of Oxford’s Atmospheric, Oceanic and Planetary Physics Department, thought Trenberth’s demands for a reversal of the burden of proof were wrong.

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“The proponents of reversing the null hypothesis should be careful of what they wish for,” concluded Curry. “One consequence may be that the scientific focus, and therefore funding, would also reverse to attempting to disprove dangerous anthropogenic climate change, which has been a position of many sceptics.”

“I doubt Trenberth’s suggestion will find much support in the scientific community,” said Professor Myles Allen from Oxford University, “but Curry’s counter proposal to abandon hypothesis tests is worse. We still have plenty of interesting hypotheses to test: did human influence on climate increase the risk of this event at all? Did it increase it by more than a factor of two?”

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All three papers are free online:

Trenberth. K, “Attribution of climate variations and trends to human influences and natural variability”: http://ift.tt/2p9T9WC

Curry. J, “Nullifying the climate null hypothesis”: http://ift.tt/2p7IOxd

Allen. M, “In defense of the traditional null hypothesis: remarks on the Trenberth and Curry opinion articles”: http://ift.tt/2pa7UJ4

Read more: Same link as above

The problem with climate science is there is no way to test the core prediction, that the Earth will heat substantially in response to anthropogenic CO2 emissions, other than to wait and see.

Important secondary predictions which should be observable by now, such as the missing tropospheric hotspot, or a projected acceleration in sea level rise, have not manifested.

Even more embarrassing, mainstream models cannot even tell us what climate sensitivity to CO2 actually is.

Is equilibrium climate sensitivity 1.5C temperature increase per doubling of CO2? Or is it 4.5C / doubling of CO2? The IPCC Fifth Assessment Summary for Policy Makers cannot give you that answer.

… The equilibrium climate sensitivity quanti es the response of the climate system to constant radiative forcing on multi- century time scales. It is de ned as the change in global mean surface temperature at equilibrium that is caused by a doubling of the atmospheric CO2 concentration. Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence)¹⁶. The lower temperature limit of the assessed likely range is thus less than the 2°C in the AR4, but the upper limit is the same. This assessment re ects improved understanding, the extended temperature record in the atmosphere and ocean, and new estimates of radiative forcing. {TS TFE.6, Figure 1; Box 12.2} …

Read more: IPCC Fifth Assessment WG1 Summary for Policy Makers (page 14)

Why is this range of possible climate sensitivities embarrassing? Consider the Charney Report, from 1979;

… We believe, therefore, that the equilibrium surface global warming due to doubled CO2 will be in the range 1.5C to 4.5 C, with the most probable value near 3°C …

Read more: http://ift.tt/2cFO2sW (page 16)

As theories are refined, key physical quantities should be resolved with greater accuracy. For example, the first measurements of the speed of light, conducted in 1676, were 26% wrong – a remarkable estimate for that period of history, but still wide of the mark. More research – better quality measurements and calculations resolved the original uncertainty about the speed of light, which is now known to a high degree of accuracy.

This failure of climate science to follow the normal scientific progression to more accurate estimates should be a serious concern. This lack of convergence on a central climate sensitivity estimate, after decades of research effort, strongly suggests something is missing from the climate models.

Whatever the missing or mishandled factor is, it has a big influence on global climate. The evidence for this is the embarrassingly broad range of estimates for climate sensitivity to a doubling of CO2, and the failure of those estimates to converge.

If climate models were capable of producing accurate predictions, if they showed any sign of converging on a reasonable climate sensitivity estimate, if predicted secondary phenomena such as the tropospheric hotspot and sea level rise acceleration were readily observable, there would be a lot less resistance to Trenberth’s apparent demand that climate model projections be accepted as somehow equivalent to empirical observations.

It should be obvious to anyone there are way too many loose ends to even come close to such acceptance.

According to the Oxford English Dictionary, the scientific method is A method of procedure that has characterized natural science since the 17th century, consisting in systematic observation, measurement, and experiment, and the formulation, testing, and modification of hypotheses.

Any suggestion that model projections should be accepted as a substitute for systematic observation and experiment, any suggestion that model output from models which have failed several key tests can be relied upon, any suggestion that defective model output constitutes proof of human influence on global climate, in my opinion utterly violates any reasonable understanding of what the scientific method should be.