Climate Dialogue about the sun

Over at Climate Dialogue we are starting a new discussion about the influence of the sun on the climate. People familiar with climate discussions know that the sun has been and still is a popular argument against the large role for greenhouse gases. This has to do with solar proxies correlating well with climate proxies (in the distant past). 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. And in fact, the science seems to be developing in the other direction, i.e. showing an even smaller solar influence than scientists thought let’s say a decade ago. 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?

So the timing of this dialogue is apt. 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?

There will be a lot of area to cover. Please head over to the dialogue and feel free to leave a public comment. Keep in mind that the goal of Climate Dialogues is to find out on what participants agree, on what they disagree and why they disagree.

 

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Is the AMO the explanation for the 1940-1970 temperature standstill?

During the past week we have had interesting discussions on this blog about a new paper that tries to filter the AMO signal out of the global temperature series. Several commenters thought that the paper contained serious flaws. Among them was Guido van der Werf, who is a scientist working at the Free University in Amsterdam. His research mainly focuses on forest fires and the effects they have on the carbon cycle. Guido is a friend and I greatly appreciate his efforts to replicate the results of the Zhou/Tung paper. He presents his finding in this guest post.

Guest post by Guido van der Werf

In a recent post Marcel Crok highlighted a new paper by Jiansong Zhou and Ka-Kit Tung in the Journal of the Atmospheric Sciences which halved recent anthropogenic warming and indicated no acceleration of anthropogenic warming over the past 100 years. If true, this is obviously a very important finding. The paper followed on two other papers by Lean and Rind (2008) and Foster and Rahmstorf (2011) aiming to disentangle anthropogenic and natural influences seen in the instrumental temperature record. Three different datasets of temperature are shown below.

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New paper cuts recent anthropogenic warming trend in half

An interesting new paper (behind paywall) has been accepted for publication in the Journal of the Atmospheric Sciences. The paper by Jiansong Zhou and Ka-Kit Tung of the University of Washington, Seattle is titled “Deducing Multi-decadal Anthropogenic Global Warming Trends Using Multiple Regression Analysis”. This paper will add fuel to the recent discussions about the nature of the global warming trend and whether it recently has stabilized or not. The authors by the way conclude it has not. Their main conclusions however is:

When the AMO is included, in addition to the other explanatory variables such as ENSO, volcano and solar influences commonly included in the multiple linear regression analysis, the recent 50-year and 32-year anthropogenic warming trends are reduced by a factor of at least two. There is no statistical evidence of a recent slow-down of global warming, nor is there evidence of accelerated warming since the mid-20th century.

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