Summary: Skeptic websites are agog with confident statements that solar cycles drive much of the decadal variation in Earth’s climate. Not only is there no clear physical mechanism, but recent analysis suggests that the historical correlation might not exist as well. Both questions lie on the frontier of science. Here are some recent papers, a selection from the vast and rapidly growing body of research on the frontiers of knowledge about this vital subject. As past comments to thei series show, true believers on both sides of the climate wars react to real science like vampires to holy water. This is the sixth in a series of posts; at the end are links to the other chapters.
This post looks at only the contrary research, that suggesting small solar effects. This debate lies on the cutting edge of solar and climate sciences. And it is a debate. Unlike the child-like views of most websites discussing climate issues, where there are only skins and shirts, right and wrong views, the FM website helps you understand both sides in these debates. Red emphasis added.
- Solar forcings of global temperatures: not big
- Solar forcing of global temperature: a small fraction of the total
- Solar trends effect on global warming: negligible
- Effect of a new grand minimum of solar activity on the future climate on Earth: small
- On the other hand, there is another side to the debate
- Effect of cosmic rays on global temperatures
- Solar effects on global temperature: not supported by the data
- We cannot know the effects of solar variation since experts cannot agree on the solar record
- Variations in Solar Irradiance — and Climate
- Other chapters in this series
- For more information: other posts about the solar cycle
(1) Solar forcings of global temperatures: not big
“How Natural and Anthropogenic Influences Alter Global and Regional Surface Temperatures: 1889 to 2006″, Judith L. Lean and David H. Rind, Geophysical Research Letters, 16 September 2008 — Free copy here. Conclusion:
None of the natural processes can account for the overall warming trend in global surface temperatures. In the 100 years from 1905 to 2005, the temperature trends produce by all 3 natural influences are at least an order of magnitude smaller than the observed surface temperature trend reported by IPCC . According to this analysis, solar forcing contributed negligible long-term warming in the past 25 years and 10% of the warming in the past 100 years, not 69% as claimed by Scafetta and West  (who assumed larger solar irradiance changes and enhanced climate response on longer time scales).
(2) Solar forcing of global temperature: a small fraction of the total
“Solar activity and the mean global temperature”, A D Erlykin, Environmental Research Letters, 20 January 2009 — Abstract:
The variation with time from 1956 to 2002 of the globally averaged rate of ionization produced by cosmic rays in the atmosphere is deduced and shown to have a cyclic component of period roughly twice the 11 year solar cycle period. Long term variations in the global average surface temperature as a function of time since 1956 are found to have a similar cyclic component. The cyclic variations are also observed in the solar irradiance and in the mean daily sun spot number. The cyclic variation in the cosmic ray rate is observed to be delayed by 2–4 years relative to the temperature, the solar irradiance and daily sun spot variations suggesting that the origin of the correlation is more likely to be direct solar activity than cosmic rays. Assuming that the correlation is caused by such solar activity, we deduce that the maximum recent increase in the mean surface temperature of the Earth which can be ascribed to this activity is less than or equal to 14% of the observed global warming.
(3) Solar trends effect on global warming: negligible
We use a suite of global climate model simulations for the 20th century to assess the contribution of solar forcing to the past trends in the global mean temperature. In particular, we examine how robust different published methodologies are at detecting and attributing solar-related climate change in the presence of intrinsic climate variability and multiple forcings. We demonstrate that naive application of linear analytical methods such as regression gives nonrobust results. We also demonstrate that the methodologies used by Scafetta and West (2005, 2006a, 2006b, 2007, 2008) are not robust to these same factors and that their error bars are significantly larger than reported. Our analysis shows that the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980.
(4) Effect of a new grand minimum of solar activity on the future climate on Earth: small
“On the effect of a new grand minimum of solar activity on the future climate on Earth“, Georg Feulner and Stefan Rahmstorf, Geophysical Research Letters, 10 March 2010 — Free copy here. Abstract:
The current exceptionally long minimum of solar activity has led to the suggestion that the Sun might experience a new grand minimum in the next decades, a prolonged period of low activity similar to the Maunder minimum in the late 17th century. The Maunder minimum is connected to the Little Ice Age, a time of markedly lower temperatures, in particular in the Northern hemisphere. Here we use a coupled climate model to explore the effect of a 21st-century grand minimum on future global temperatures, finding a moderate temperature offset of no more than −0.3°C in the year 2100 relative to a scenario with solar activity similar to recent decades. This temperature decrease is much smaller than the warming expected from anthropogenic greenhouse gas emissions by the end of the century.
(5) On the other hand, there is another side to the debate
(a) “An influence of solar spectral variations on radiative forcing of climate“, Joanna D. Haigh, Nature, 7 October 2010 — Free copy here. Conclusion:
The SIM data provide an entirely different picture from the one currently accepted for the variation of solar irradiance. It is pertinent to ask whether this spectral variability is typical of solar activity cycles and, if so, why it has not been observed previously. It is possible that the Sun has been behaving in an anomalous fashion recently; certainly the current solar minimum is lower and longer than any of those observed over recent decades and perhaps the solar spectrum has different characteristics when the Sun is in a state of very low activity. Gaps in understanding will only be resolved by the acquisition of long-term, well-calibrated, high-vertical-resolution measurements of stratospheric composition and temperature acquired coincidently with essential solar spectral data that have also been properly degradation-corrected and calibrated.
The SORCE observations are, however, consistent with a solar activity-dependent change in the temperature gradient of the solar photosphere, suggesting that the offsetting irradiance trends with wavelength seen in SIM should appear in each solar cycle. If this is the case, then it is necessary to reconsider the current understanding of the mechanisms whereby solar cycle variability influences climate: the impact on the stratosphere is much larger than previously thought and the radiative forcing of surface climate is out of phase with solar activity. At present there is no evidence to ascertain whether this behaviour has occurred before, but if this were the case during previous multi-decadal periods of low solar activity it would be necessary to revisit assessments of the solar influence on climate and to revise the methods whereby these are represented in global models.
Update: (b) “The long sunspot cycle 23 predicts a significant temperature decrease in cycle 24“, Jan-Erik Solheim et al, submitted to the Journal of Atmospheric and Solar-Terrestrial Physics, 10 February 2012 — Abstract:
Relations between the length of a sunspot cycle and the average temperature in the same and the next cycle are calculated for a number of meteorological stations in Norway and in the North Atlantic region. No significant trend is found between the length of a cycle and the average temperature in the same cycle, but a significant negative trend is found between the length of a cycle and the temperature in the next cycle. This provides a tool to predict an average temperature decrease of at least 1.0 ◦C from solar cycle 23 to 24 for the stations and areas analyzed.
We find for the Norwegian local stations investigated that 25–56% of the temperature increase the last 150 years may be attributed to the Sun. For 3 North Atlantic stations we get 63–72% solar contribution. This points to the Atlantic currents as reinforcing a solar signal.
(6) Effect of cosmic rays on global temperatures: small
“The contribution of cosmic rays to global warming“, T. Sloan and A. W. Wolfendal, Journal of Atmospheric and Solar-Terrestrial Physics, October 2011 — Abstract:
A search has been made for a contribution of the changing cosmic ray intensity to the global warming observed in the last century. The cosmic ray intensity shows a strong 11 year cycle due to solar modulation and the overall rate has decreased since 1900. These changes in cosmic ray intensity are compared to those of the mean global surface temperature to attempt to quantify any link between the two. It is shown that, if such a link exists, the changing cosmic ray intensity contributes less than 8% to the increase in the mean global surface temperature observed since 1900.
(7) Solar effects on global temperature: not supported by the data
“Are secular correlations between sunspots, geomagnetic activity, and global temperature significant?“, Jeffrey J. Love et al, Geophysical Research Letters, 11 November 2011 — Free copy here. Abstract:
Recent studies have led to speculation that solar-terrestrial interaction, measured by sunspot number and geomagnetic activity, has played an important role in global temperature change over the past century or so. We treat this possibility as an hypothesis for testing. We examine the statistical significance of cross-correlations between sunspot number, geomagnetic activity, and global surface temperature for the years 1868–2008, solar cycles 11–23.
The data contain substantial autocorrelation and nonstationarity, properties that are incompatible with standard measures of cross-correlational significance, but which can be largely removed by averaging over solar cycles and first-difference detrending. Treated data show an expected statistically significant correlation between sunspot number and geomagnetic activity, Pearson p < 10−4, but correlations between global temperature and sunspot number (geomagnetic activity) are not significant, p = 0.9954, (p = 0.8171).
In other words, straightforward analysis does not support widely-cited suggestions that these data record a prominent role for solar-terrestrial interaction in global climate change. With respect to the sunspot-number, geomagnetic-activity, and global-temperature data, three alternative hypotheses remain difficult to reject:
- the role of solar-terrestrial interaction in recent climate change is contained wholly in long-term trends and not in any shorter-term secular variation, or,
- an anthropogenic signal is hiding correlation between solar-terrestrial variables and global temperature, or,
- the null hypothesis, recent climate change has not been influenced by solar-terrestrial interaction.
(8) We cannot know the effects of solar variation since experts cannot agree on the solar record
“The Long-term Variation of Solar Activity“, Leif Svalgaard, Nagoya Workshop on the Relationship between Solar Activity and Climate Changes, 16 January 2012 — Conclusions:
- Solar Activity is now back to what it was a century ago
- No Modern Grand Maximum
- Cosmic Ray Modulation discordant
- Experts cannot agree on the Long-term variation of solar activity
- Solar influence on Climate on shaky ground if we don’t even know solar input
(9) Variations in Solar Irradiance — and Climate
“Variations in Solar Irradiance and Climate“, Judith Lean”, Nagoya Workshop on the Relationship between Solar Activity and Climate Changes, 16 January 2012 — Conclusions:
Slide 9: There are Many Causes of Climate, Atmosphere and Ozone Change
Natural Forcings: solar variability and volcanic eruptions
Internal Oscillations: El Nino Southern Oscillation, North Atlantic Oscillation, Quasi biennial Oscillation
- atmospheric GH gases – CO2, CH4, CFCs, O3, N2O
- tropospheric aerosols – direct and indirect effects of soot, sulfate, carbon, biomass burning, soil dust
- land cover changes
Slide 41: Conclusion: A new Maunder Minimum will NOT cause another Little Ice Age
(10) Chapters in this series
- What we know about our past climate, and its causes
- Good news! Global temperatures have stabilized, at least for now.
- Is it possible to debate climate change with true believers? See the replies to Thursday’s post. Comments welcomed!
- What can climate scientists tell about the drivers of future warming?
- What can climate scientists tell us about the drivers of future warming? – part two of two
- The slow solar cycle is getting a lot of attention. What are its effect on us?
- What we’re learning about climate, and recommendations
(11) For More Information: other posts about the solar cycle
- NASA: Sun undergoing a “deep solar minimum”, 13 April 2009
- The Unusually Quiet Sun finally gets some attention, 23 April 2009
- A brief look at the Sun’s influence on Earth’s climate, 4 May 2009
- Big news from NASA about the causes of climate change!, 6 June 2009 — About solar effects
- Peer reviewed science: breakthoughs about the sun’s impact on Earth’s climate, 4 September 2009
- Another climate wild card: solar cycle 24, perhaps causing food riots during the next decade, 1 February 2011
- Update about the weather – on the Sun. Perhaps coming soon to Earth., 9 February 2011