Declining solar activity linked to recent warming

The Sun may have caused as much warming as carbon dioxide over three years.

An analysis of satellite data challenges the intuitive idea that decreasing solar activity cools Earth, and vice versa. In fact, solar forcing of Earth’s surface climate seems to work the opposite way around — at least during the current Sun cycle.

Joanna Haigh, an atmospheric physicist at Imperial College London, and her colleagues analysed daily measurements of the spectral composition of sunlight made between 2004 and 2007 by NASA’s Solar Radiation and Climate Experiment (SORCE) satellite. They found that the amount of visible light reaching Earth increased as the Sun’s activity declined — warming the Earth’s surface. Their unexpected findings are published today in Nature.

An influence of solar spectral variations on radiative forcing of climate

Haigh, J. D., Winning, A. R., Toumi, R. & Harder, J. W. Nature 467, 696-699 (2010).

The thermal structure and composition of the atmosphere is determined fundamentally by the incoming solar irradiance. Radiation at ultraviolet wavelengths dissociates atmospheric molecules, initiating chains of chemical reactions—specifically those producing stratospheric ozone—and providing the major source of heating for the middle atmosphere, while radiation at visible and near-infrared wavelengths mainly reaches and warms the lower atmosphere and the Earth’s surface1. Thus the spectral composition of solar radiation is crucial in determining atmospheric structure, as well as surface temperature, and it follows that the response of the atmosphere to variations in solar irradiance depends on the spectrum2. Daily measurements of the solar spectrum between 0.2 µm and 2.4 µm, made by the Spectral Irradiance Monitor (SIM) instrument on the Solar Radiation and Climate Experiment (SORCE) satellite3 since April 2004, have revealed4 that over this declining phase of the solar cycle there was a four to six times larger decline in ultraviolet than would have been predicted on the basis of our previous understanding. This reduction was partially compensated in the total solar output by an increase in radiation at visible wavelengths. Here we show that these spectral changes appear to have led to a significant decline from 2004 to 2007 in stratospheric ozone below an altitude of 45 km, with an increase above this altitude. Our results, simulated with a radiative-photochemical model, are consistent with contemporaneous measurements of ozone from the Aura-MLS satellite, although the short time period makes precise attribution to solar effects difficult. We also show, using the SIM data, that solar radiative forcing of surface climate is out of phase with solar activity. Currently there is insufficient observational evidence to validate the spectral variations observed by SIM, or to fully characterize other solar cycles, but our findings raise the possibility that the effects of solar variability on temperature throughout the atmosphere may be contrary to current expectations.

The Abstract states:

Solar activity during the current sunspot minimum has fallen to levels unknown since the start of the 20th century. The Maunder minimum (about 1650–1700) was a prolonged episode of low solar activity which coincided with more severe winters in the United Kingdom and continental Europe. Motivated by recent relatively cold winters in the UK, we investigate the possible connection with solar activity. We identify regionally anomalous cold winters by detrending the Central England temperature (CET) record using reconstructions of the northern hemisphere mean temperature. We show that cold winter excursions from the hemispheric trend occur more commonly in the UK during low solar activity, consistent with the solar influence on the occurrence of persistent blocking events in the eastern Atlantic. We stress that this is a regional and seasonal effect relating to European winters and not a global effect. Average solar activity has declined rapidly since 1985 and cosmogenic isotopes suggest an 8% chance of a return to Maunder minimum conditions within the next 50 years (Lockwood 2010 Proc. R. Soc. A 466 303–29): the results presented here indicate that, despite hemispheric warming, the UK and Europe could experience more cold winters than during recent decades.

See also the BBC News website: Low solar activity link to cold UK winters

CRN comment: Despite the global warming spin applied to this paper, we can make a number of comments including:

This paper provides another example of the significant effect of solar activity on climate.

Climate has strong regional variations not refelected by the flawed metric of a ‘global average temperature.’

The governments of the UK/Europe and around the world are preparing for warming, not cooling.

The Little Ice Age linked to the solar ‘Maunder Minimum’ had a global effect with regional diffrences – we can even see evidence of the LIA in Australia, which isn’t terribly close to Europe (e.g. Pollack, H. N., Huang, S. and Smerdon, J. E. 2006. Five centuries of climate change in Australia: the view from underground. J. Quaternary Sci., Vol. 21 pp. 701–706. ISSN 0267–8179)

Scientists from NASA’s Langley Research Center and Hampton University in Hampton, Va., and the National Center for Atmospheric Research in Boulder, Colo., will present these results at the fall meeting of the American Geophysical Union in San Francisco from Dec. 14 to 18.

Read more here.

physicsworld.com: ‘The Sun could be heading into period of extended calm’

The Abstract states:

The solar contribution to global mean air surface temperature change is analyzed by using an empirical bi-scale climate model characterized by both fast and slow characteristic time responses to solar forcing. Since 1980 the solar contribution to climate change is uncertain because of the severe uncertainty of the total solar irradiance satellite composites. The sun may have caused from a slight cooling, if PMOD TSI composite is used, to a significant warming (up to 65% of the total observed warming) if ACRIM, or other TSI composites are used. The model is calibrated only on the empirical 11-year solar cycle signature on the instrumental global surface temperature since 1980. The model reconstructs the major temperature patterns covering 400 years of solar induced temperature changes, as shown in recent paleoclimate global temperature records.

The Conclusion states:

Herein I have analyzed the solar contribution to global mean air surface temperature change. A comprehensive interpretation of multiple scientific findings indicates that the contribution of solar variability to climate change is significant and that the temperature trend since 1980 can be large and upward. However, to correctly quantify the solar contribution to the recent global warming it is necessary to determine the correct TSI behavior since 1980. Unfortunately, this cannot be done with certainty yet. The PMOD TSI composite, which has been used by the IPCC and most climate modelers, has been found to be based on arbitrary and questionable assumptions (Scafetta and Willson, 2009). Thus, it cannot be excluded that TSI increased from 1980 to 2000 as claimed by the ACRIM scientific team.

The IPCC (2007) claim that the solar contribution to climate change since 1950 is negligible may be based on wrong solar data in addition to the fact that the EBMs and GCMs there used are missing or poorly modeling several climate mechanisms that would significantly amplify the solar effect on climate. When taken into account the entire range of possible TSI satellite composite since 1980, the solar contribution to climate change ranges from a slight cooling to a significant warming, which can be as large as 65% of the total observed global warming.

The above wide range strongly contrasts with some recent estimates such as those found by Lockwood, 2008 M. Lockwood, Recent changes in solar output and the global mean surface temperature. III. Analysis of the contributions to global mean air surface temperature rise, Proc. R. Soc. A 464 (2008), pp. 1–17 10.1098/rspa.2007.0348.Lockwood (2008), who calculated that the solar contribution to global warming is negligible since 1980: the sun could have caused from a -3.6% using PMOD to a +3.1% using ACRIM. In fact, Lockwood’s model is approximately reproduced by the ESS1 curve that refers to the solar signature on climate as produced only by those processes characterized with a short time response to a forcing. Indeed, the characteristic time constants that Lockwood found with his complicated nonlinear multiregression analysis are all smaller than one year (see his table 1) and the climate sensitivity to TSI that he found is essentially equal to my k1S! Likely, Lockwood’s model was unable to detect the climate sensitivity to solar changes induced by those climate mechanisms that have a decadal characteristic time response to solar forcing: mechanisms that must be present in nature for physical reasons. As proven above, these mechanisms are fundamental to properly model the decadal and secular trends of the temperature because they yield high climate sensitivities to solar changes.

Analogously, my findings contrast with Lean and Rind (2008), who estimated that the sun has caused less than 10% of the observed warming since 1900. The model used by Lean and Rind, like Lockwood’s model, is not appropriate to evaluate the multidecadal solar effect on climate. In fact, Lean and Rind do not use any EBM to generate the waveforms they use in their regression analysis. These authors assume that the temperature is just the linear superposition of the forcing functions with some fixed time-lags. They also ignore ACRIM TSI satellite composite. While Lean and Rind’s method may be sufficiently appropriate for determining the 11-year solar cycle signature on the temperature records there used, the same method is not appropriate on multidecadal scales because climate science predicts that time-lag and the climate sensitivity to a forcing is frequency dependent. Consequently, as Lockwood’s model, Lean and Rind’s model too misses the larger sensitivity that the climate system is expected to present to solar changes at the decadal and secular scales.

I have shown that the processes with a long time response to climate forcing are fundamental to correctly understanding the decadal and secular solar effect on climate (see ESS2 curve). With simple calculations it is possible to determine that if the climate parameters (such as the albedo and the emissivity, etc.) change slowly with the temperature, the climate sensitivity to solar changes is largely amplified as shown in Eq. (10).

This finding suggests that the climate system is hypersensitive to the climate function h(T) and even small errors in modeling h(T) (for example, in modeling how the albedo, the cloud cover, water vapor feedback, the emissivity, etc. respond to changes of the temperature on a decadal scale) would yield the climate models to fail, even by a large factor, to appropriately determine the solar effect on climate on decadal and secular scale. For similar reasons, the models also present a very large uncertainty in evaluating the climate sensitivity to changes in CO2 atmospheric concentration (Knutti and Hegerl, 2008). This large sensitivity of the climate equations to physical uncertainty makes the adoption of traditional EBMs and GCMs quite problematic.

About the result depicted in Fig. 6, the ESS curve has been evaluated by calibrating the proposed empirical bi-scale model only by using the information deduced: (1) by the instrumental temperature and the solar records since 1980 about the 11-year solar signature on climate; (2) by the findings by Scafetta (2008) and Schwartz (2008) about the long and short characteristic time responses of the climate as deduced with autoregressive models. The paleoclimate temperature reconstructions were not used to calibrate the model, as done in Scafetta and West (2007). Thus, the finding shown in Fig. 6 referring to the preindustrial era has also a predictive meaning, and implies that climate had a significant preindustrial variability which is incompatible with a hockey stick temperature graph.

RC’s Benestad and Schmidt (let’s call them ‘BS’ for shortness!) have recently published a paper in JGR. (Benestad, R. E., and G. A. Schmidt (2009), Solar trends and global warming, J. Geophys. Res., 114, D14101, doi:10.1029/2008JD011639).

Peer review is often only cursory, and Scafetta has responded via Roger Pielke Sr’s Climate Science weblog, in advance of his comment on the BS paper being published via the peer review process, which will take several months. Now, you just know that when an RC scientist uses the word ‘robust’ that it just ain’t so. Indeed, BS used the word ‘robust’ and its derivatives no less than 18 times. BS have been invited to respond to Scafetta’s comments by Roger Pielke Sr.

Meanwhile, the truth is that the Sun-Climate link is poorly understood. Even the IPCC rate the level of scientific understanding (LOSU) of Solar Irradiance as ‘Low’ and the LOSU for other Solar factors is even lower. However, there are those who don’t want the solar influence to be understood in any way that detracts from AG alarmism and ‘magical’ climate policy solutions. Tough!

The Abstract states:

We have studied solar variations during the Holocene (i.e. last ~11,700 yr) by combining a new model of the Earth’s dipole moment with 14C data from the IntCal04 record and 10Be data from the GRIP ice core. Joint spectral analysis of the two nuclide records suggests that the periodic behavior of the Sun was particularly pronounced between 6000-4500 yr BP and 3000-2000 yr BP, with dominating periodicities of ~88, ~150, ~220, and ~400 years, while this rhythmic behavior faded during other time intervals. The fact that the two reconstructions, based on radionuclides with distinct geochemical properties, agree with respect to both the frequency and timing of the periodic behavior, strongly suggests that they reflect the actual behavior of the Sun. Subtle but systematic differences between the amplitude spectra may point to an interplay between the climate system and the ~220- and ~400-year solar cycles during intervals when these were particularly prominent.

In the results and Discussion the authors state:

The dominant periodicities observed in this study are ~88, ~150, ~220, ~400 years, which generally agrees with previous studies of 14C records [Stuiver and Braziunas, 1989; 1993; Damon and Sonnett, 1991]. The combined power spectrum also suggests that periodicities longer than ~1000 years exist, in particular around 3000 and 7500 yr BP (Fig. 2c), but, because the FFT (solar magnetic field: spectral analysis) approach used here is designed to localize the solar cycles in time, we cannot also discriminate reliably between solar cycles of ~1500 and ~2200 years (somewhat analogous to Heisenberg’s uncertainty principle). The most likely cause for the periodicities <500 years is the varying Sun because geomagnetic field intensity variations would have been unrealistically large to cause similar high-frequency, large-amplitude changes in radionuclide production [Snowball and Muscheler, 2007]. Most interestingly, both reconstructions indicate that the amplitudes of the solar periodicities varied significantly in time. The solar cycles were particularly prominent during the time intervals 6000-4500 yr BP and 3000-2000 yr BP, whereas this periodic behavior faded during other time intervals. The Gleissberg cycle, however, which was most prominent between 4000 and 6000 yr BP, was surprisingly vague from ~3500 yr BP onwards. Hence, although it remains complicated to reconstruct the long-term Holocene solar variability (Fig. 1), our analysis of spectral power through time robustly demonstrates that the behavior of the Sun did vary on these timescales.

and:

Nevertheless, in the light of the paleoevidence for a solar influence on climate, it seems possible that the ~220- and ~400-year solar cycles influenced the climate system in particular between 6000 and 4500 yr BP and between 3000 and 2000 yr BP, but it remains difficult to resolve whether it was the 14C signal, the 10Be signal, or both, that reflect the climate response. Interestingly, both these intervals coincide with periods of significant reorganization of the ocean and atmosphere circulation in the North Atlantic region [Kaplan and Wollfe, 2006; Seidenkrantz et al., 2007].

The Abstract states:

Close passages of coronal mass ejections from the sun are signaled at the Earth’s surface by Forbush decreases in cosmic ray counts. We find that low clouds contain less liquid water following Forbush decreases (FDs), and for the most influential events the liquid water in the oceanic atmosphere can diminish by as much as 7%. Cloud water content as gauged by the Special Sensor Microwave/Imager (SSM/I) reaches a minimum around 7 days after the Forbush minimum in cosmic rays, and so does the fraction of low clouds seen by the Moderate Resolution Imaging Spectroradiometer (MODIS) and in the International Satellite Cloud Climate Project (ISCCP). Parallel observations by the aerosol robotic network AERONET reveal falls in the relative abundance of fine aerosol particles which, in normal circumstances, could have evolved into cloud condensation nuclei (CCN). Thus a link between the sun, cosmic rays, aerosols, and liquid-water clouds appears to exist on a global scale.

The paper concludes:

Our results show global-scale evidence of conspicuous influences of solar variability on cloudiness and aerosols. Irrespective of the detailed mechanism, the loss of ions from the air during FDs reduces the cloud liquid water content over the oceans. So marked is the response to relatively small variations in the total ionization, we suspect that a large fraction of Earth’s clouds could be controlled by ionization. Future work should estimate how large a volume of the Earth’s atmosphere is involved in the ion process that leads to the changes seen in CCN and its importance for the Earth’s radiation budget. From solar activity to cosmic ray ionization to aerosols and liquid-water clouds, a causal chain appears to operate on a global scale.

Svensmark, H., T. Bondo, and J. Svensmark (2009),

Cosmic ray decreases affect atmospheric aerosols and clouds,

Geophys. Res. Lett., doi:10.1029/2009GL038429, in press.

(accepted 17 June 2009)

The Abstract states:

Daily temperature and pressure series from 55 European meteorological stations covering the 20th century are analyzed. The overall temperature mean displays a sharp minimum near 1940 and a step-like jump near 1987. We evaluate the evolution of disturbances of these series using mean squared inter-annual variations and “lifetimes”. The decadal to secular evolutions of solar activity and temperature disturbances display similar signatures over the 20th century. Because of heterogeneity of the climate system response to solar forcing, regional and seasonal approaches are key to successful identification of these signatures. Most of the solar response is governed by the winter months, as best seen near the Atlantic Ocean. Intensities of disturbances vary by factors in excess of 2, underlining a role for the Sun as a significant forcing factor of European atmospheric variations. We speculate about the possible origin of these solar signatures. The last figure of the paper exemplifies its main results.

The paper concludes:

In concluding, we find increasingly strong evidence of a clear solar signature in a number of climatic indicators in Europe, strengthening the earlier conclusions of a study that included stations from the United States (Le Mouël et al., 2008). With the recent downturn of both solar activity and global temperatures, the debated correlations we suggested in Le Mouël et al. (2005), which appeared to stop in the 1980s, actually might extend to the present. The role of the Sun in global and regional climate change should be re-assessed and reasonable physical mechanisms are in sight.

Fairbridge, R. W. and Shirley, J. H. (1987): Prolonged minima and the 179-year cycle of the solar inertial motion. Solar Physics 110, 191-220.

Abstract:

The authors employ the JPL long ephemeris DE-102 to study the inertial motion of the Sun for the period A.D.760 – 2100. Defining solar orbits with reference to the Sun’s successive close approaches to the solar system barycenter, occurring at mean intervals of 19.86 yr, they find simple relationships linking the inertial orientation of the solar orbit and the amplitude of the precessional rotation of the orbit with the occurrence of the principal prolonged solar activity minima of the current millenium (the Wolf, Spörer, and Maunder minima). The progression of the inertial orientation parameter is controlled by the 900-yr “great inequality” of the motion of Jupiter and Saturn, while the precessional rotation parameter is linked with the 179-yr cycle of the solar inertial motion previously identified by Jose (1965). A new prolonged minimum of solar activity may be imminent.

Landscheidt T. (2003): New Little Ice Age Instead of Global Warming? Energy & Environment, Volume 14, Numbers 2-3, 1 May 2003 , pp. 327-350(24)

Abstract:

Analysis of the sun’s varying activity in the last two millennia indicates that contrary to the IPCC’s speculation about man-made global warming as high as 5.8°C within the next hundred years, a long period of cool climate with its coldest phase around 2030 is to be expected. It is shown that minima in the secular Gleissberg cycle of solar activity, coinciding with periods of cool climate on Earth, are consistently linked to an 83-year cycle in the change of the rotary force driving the sun’s oscillatory motion about the centre of mass of the solar system. As the future course of this cycle and its amplitudes can be computed, it can be seen that the Gleissberg minimum around 2030 and another one around 2200 will be of the Maunder minimum type accompanied by severe cooling on Earth. This forecast should prove ‘skilful’ as other long-range forecasts of climate phenomena, based on cycles in the sun’s orbital motion, have turned out correct, as for instance the prediction of the last three El Niños years before the respective event.

Outlook:

“We need not wait until 2030 to see whether the forecast of the next deep Gleissberg minimum is correct. A declining trend in solar activity and global temperature should become manifest long before the deepest point in the development. The current 11-year sunspot cycle 23 with its considerably weaker activity seems to be a first indication of the new trend, especially as it was predicted on the basis of solar motion cycles two decades ago. As to temperature, only El Nino periods should interrupt the downward trend, but even El Ninos should become less frequent and strong. The outcome of this further long-range climate forecast solely based on solar activity may be considered to be a touchstone of the IPCC’s hypothesis of man-made global warming.”