by Judith Curry
Climate Dialogue has a very interesting discussion What will happen during a new Maunder Minimum? This is my favorite Climate Dialogue so far.
Climate Dialogue is a remarkable blogospheric experiment. From the About page:
[Climate Dialogue is] an international blog where invited scientists discuss controversial topics in climate science. There are several blogs that facilitate discussions between climate experts but since the climate debate is highly polarized and politicized, blog discussions between experts with opposing views are rare.
ClimateDialogue.org is the result of a request by the Dutch parliament to facilitate the scientific discussions between climate experts representing the full range of views on the subject. It is funded by the Dutch Ministry of Infrastructure and the Environment.
The aim of ClimateDialogue.org is to establish what the discussants agree on, where disagreements remain and what the possible or likely reasons behind these disagreements are. The project by no means aims to solve controversies nor give an objective, scientific final judgment on the topics under discussion.
In case you missed it, I participated in the inaugural discussion on Arctic sea ice.
Marcel Crok provides an introduction to the current dialogue at WUWT, excerpts:
People familiar with climate discussions know that the sun has been and still is a popular argument to explain at least part of the warming since 1750. Also the Little Ice Age coincided with the Maunder Minimum, a period with few visible sunspots. So if the sun played a role in the past, why shouldn’t it in the present?
But figuring out how the sun has varied in e.g. the past millennium isn’t easy. AR5 said that in terms of radiative forcing since 1750 the influence of the sun is almost negligible.
Meanwhile solar activity has dropped to levels last seen a century ago. Some scientists suggest the sun might go into a new Maunder Minimum in the coming decades. What influence will that have on our climate?
We have a record number of participants, namely five. Two of them – Nicola Scafetta (USA) and Jan-Erik Solheim (NOR) – believe in a large role of the sun. Mike Lockwood (GBR) – in line with AR5 – thinks the sun is only a minor player. The two other participants – Ilya Usoskin (FIN) and José Vaquero (ESP) – seem somewhere in between.
In our Introduction we asked the participants the following questions:
1) What is according to you the “best” solar reconstruction since 1600 (or even 1000) in terms of Total Solar Irradiance?
2) Was there a Grand Solar Maximum in the 20th century?
3) What is your preferred temperature reconstruction for the same period? How much colder was the Little Ice Age than the current warm period?
4) What is the evidence for a correlation between global temperature and solar activity?
5) How much of the warming since pre-industrial would you attribute to the sun?
6) Is the Total Solar Irradiance (TSI) of the sun all that matters for the Earth’s climate? If not, what amplification processes are important and what is the evidence these play a role?
7) what is the sun likely going to do in the next few decades and what influence will it have on the climate? Is there consensus on the predictability of solar variability?
The Climate Dialogue moderators have prepared a VERY GOOD Introduction that provides context and summarizes they key issues surrounding the main questions and issues under debate.
Mike Lockwood pretty much articulates a position that is consistent with the AR5 – the sun plays only a very minor role. He prefers the PMOD version of the TSI measurements. He acknowledges that there is some evidence for solar influence on regional/seasonal climates.
Nicola Scafetta argues that the Sun has a significant influence on the climate. Scafetta’s essay does a very good job outlining his overall approach and reasoning framework for his research – something that seems missing in his individual papers. His concluding paragraph:
After having noted that not even CO2 and other greenhouse gases, either of natural or of anthropogenic origin, could be the cause, let alone the primary cause, of global climate changes, Quinn (2010) wrote: “Evidence indicates that global warming is closely related to a wide range of solar-terrestrial phenomenon, from the sun’s magnetic storms and fluctuating solar wind all the way to the Earth’s core motions. Changes in the Solar and Earth magnetic fields, changes in the Earth’s orientation and rotation rate, as well as the gravitational effects associated with the relative barycenter motions of the Earth, Sun, Moon, and other planets, all play key roles. Clear one-to-one correspondence exists among these parameters and the Global Temperature Anomaly on three separate time scales.”
Jan-Erik Solheim is the most skeptical of the essays – most of the 20th century warming is due to the Sun. Solheim (and Scafetta) prefer the ACRIM data to the PMOD, and Solheim supports the Hoyt and Schatten reconstruction. He presents the arguments for a Grand Solar Maximum in the 20th century. His conclusion: Evaluating these parameters, I arrive at the conclusion that the global temperature may during the next solar deep minimum fall to a level slightly higher than around 1900 which means -0.6 ±0.2 °C relative to the last decade.
Ilya Usoskin emphasizes uncertainty. His concluding statement is: Concerning the influence on climate, I think we are unable at the moment to make a realistic assessment to what will be the consequence, since many processes are still poorly understood and modelled.
Jose Vaquero states that he is fairly skeptical about a new Maunder Minimum. My personal opinion is that we don’t have a clear definition of Grand Episodes (Maxima and Minima), including the Maunder Minimum. I am in fact pretty skeptical about the possibility of a new great episode. I think we do not know enough about how the solar dynamo works and, therefore, it is not possible to offer predictions. In fact, the studies that suggest a Grand sunspot minimum are based on observational aspects and not on the physics of the Sun.
For additional context, see my previous solar posts:
- IPCC: solar variations don’t matter
- Effects of solar variability on climate
- 21st century solar cooling
- Solar discussion thread
- Solar snooze discussion thread
It seems that there is a lot more uncertainty about Sun-climate connections than acknowledged by the IPCC (and incorporated into attribution and climate sensitivity analyses.) A critical issue in sorting this out is the debate about PMOD versus ACRIM observations/analyses. This is apparently not settled, and I’m not sure how this will be settled going forward.
I really like having 5 experts contribute essays – the previous Dialogues have only had 3 experts. CD has been having difficulty in getting experts to participate, particularly on the ‘consensus’ side. Most scientists aren’t accustomed to participating in the blogosphere. In the solar discussion, unfortunately there have been very few comments, especially from the experts. Maybe the discussion will pick up.
And of course I encourage dialogue on this topic here!