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Andrew McRae's comment

Harry, re:#29, you asked:

"1. Does the Maunder Minimum actually coincide with the period of global climate change?"

The period of extremely low solar magnetic activity according to astronomers’ sunspot observations at the time began in 1610. According to the Loehle 2008 reconstruction of world temperature, temperatures being above -0.4 degrees anomaly prior to 1610 and below -0.4 after 1610 for ~100 years are within the 95% confidence interval of that reconstruction.

The power of cosmic ray flux to alter climate on earth is also indisputable as the correlation appears at all time scales, from weather balloons and neutron counters on scales of a decade [Uoskin 2004], in cave stalactites at scales of several millenia [Fig 1, Neff 2001], and in iron meteorites and paleoclimate proxies that span the ice ages over 700 million years [Shaviv 2002].

As correlations between solar magnetic activity and regional temperature have been found on pretty much every timescale tested, it would be utterly bizarre if the Maunder minimum had not caused the LIA.

Okay, a quote from Veizer 2005, regarding natural solar attribution of climate change:

"Moreover, taking into account the empirical evidence, such as the unprecedented solar activity during the late 20th century (Fig. 13) or the coeval decline in global albedo (“earthshine”) (Fig. 15), and considering that the 1915-1999 TSI trend from the Mt. Wilson and Sacramento Peak Observatories can explain 80% of the 11-year smoothed variance in global temperature (Foukal, 2002), the celestial cause as a primary driver again appears to be a more consistent explanation."

Against this background of (hmm what’s the phrase) “overwhelming evidence” it is easier to question the dating reliability of temperature proxies (such as Loehle’s subset) than to question the solar/climate causal connection.

"2. Was the global climate change actually global, or was it restricted to one hemisphere or even to one region?"

Red herring. Look at any modern map of regional temperature warming rates and you will see the world today is not all warming equally at the same rate. The past would not be any different. If all areas were required to warm at the same rate at the same time and reach maximum anomaly synchronously before it would qualify as a global climate change, then the Current Warm Period would not qualify as a global warm period. Smile

Despite being a red herring, as I showed earlier, the dating is nontheless compatible within the 95% bounds.

"3. If feedbacks are required to amplify any small changes in the sun’s TSI into significant global climate change, what were they?"

Small?? The Sun’s TSI changes by 2W/m^2 between a peak and trough in a single cycle, by 0.5W/m^2 between adjacent cycle troughs, by 1+ W/m^2 between distant cycles, and by several W/m^2 in longer term cycles on the order of 172 years or so. Considering a 3.7W/m^2 increment is supposed to be “dangerous”, the sort of TSI drop that is estimated from the Maunder minimum could not credibly be called “small”.

"4. If a small change in the sun did cause the global climate change, what does that say about climate sensitivity to external forcing?"

You say “forcing” like you mean TSI, but you’ve been told many times now that solar magnetic activity significantly affects earth’s climate, most likely by some combination of cloud seeding and UV ozone depletion. Just a 1% change in cloud cover will cause a 13W/m^2 insolation difference, about three times greater than a doubling of CO2. It’s really not small, Harry. This solar effect is visible in the climate proxies referenced above regardless of our ability to determine how much of that net result was “primary” and how much was “feedback”. We know the end result of forcing+feedback for the past, because that sum is whatever was measured.

Wishing you continued luck in your search for the facts about natural climate variability.
It is our attitude toward free thought and free expression that will determine our fate. There must be no limit on the range of temperate discussion, no limits on thought. No subject must be taboo. No censor must preside at our assemblies.

–William O. Douglas, U.S. Supreme Court Justice, 1952

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