Cosmic rays and Earth's climate
Also available are some pretty nice animations:
These animations illustrate the physical process which the theory about the cosmic connection to Earth's climate proposes: 1) A giant star explodes in a supernova explosion and emits cosmic rays, 2) cosmic rays enter Earth's atmosphere, 3) rays release free electrons which act a catalysts for the building blocks for cloud condensation nuclei, 4) on which water vapour condenses into clouds.
Uncompressed AVI-animation (97 MB) or Compressed AVI-animation (41 MB) Note: we found the animation files very slow to download so, if you can't get them we have local copies here for the uncompressed and here for the compressed version. Naturally we prefer you get them direct from the source.
Now, some will fail to read the linked or provided documents or simply fail to understand the significance of this work so let's expand on this somewhat.
Firstly, this new work is a severe blow to proponents of the enhanced greenhouse hypothesis and advocates of Anthropogenic Global Warming who have worked so hard to deny solar influence on global climate. Recall that we had this in September of this year:
<chuckle> Now they're turning down the sun: "Study acquits sun of climate change, blames humans" - "OSLO - The sun's energy output has barely varied over the past 1,000 years, raising chances that global warming has human rather than celestial causes, a study showed on Wednesday. Researchers from Germany, Switzerland and the United States found that the sun's brightness varied by only 0.07 percent over 11-year sunspot cycles, far too little to account for the rise in temperatures since the Industrial Revolution." (Reuters) | Changes in solar brightness too weak to explain global warming (NCAR/UCAR)
Such claims of solar variation insufficiency survive because indications of feedback mechanisms were supported only by historical records and statistical associations but were not empirically demonstrated (never mind that situation applies particularly to the enhanced greenhouse hypothesis, the simple fact is that hypothesis is currently politically correct and hence requires no evidentiary support). This situation has now changed because Svensmark and the team at the Danish National Space Center have experimentally demonstrated the very mechanism they proposed a decade ago.
How big a deal is this indirect cloud effect? Huge, actually. In just 5 years it was responsible for a 2% decrease in low clouds (the kind that reflect incoming solar radiation by day) which, in turn, equates to an increase in surface warming of 1.2 Wm-2 from incident radiation -- equivalent to some 85% of the IPCC's estimate for the effect of all carbon dioxide increase since the Industrial Revolution.
Significantly, the "Svensmark Effect" only operates in the lower troposphere because there is always more than sufficient ionization of the upper atmosphere to ensure no shortage of cloud nuclei. This is important since high, thin clouds do not reflect incoming sunlight and are a net warming influence while the reverse is true of low, bright clouds. The effect then directly influences cooling cloud cover.
Note that this is only part of the story since, as far as we are aware, no one has yet investigated a counterintuitive parallel effect -- condensation and precipitation will likely reduce the total lower atmospheric concentration of that ubiquitous greenhouse gas, water vapor, so increasing clear sky radiative cooling. It's true that clouds account for roughly one-fifth of the greenhouse effect but gaseous water vapor accounts for more than one-half of the total effect. Reduced condensation then would leave an increased proportion of gaseous water vapor with corresponding increase in clear sky greenhouse effect.
Of course, Svensmark et al are not alone in associating solar activity and cloudiness, see for example, Influence of Solar Activity on State of Wheat Market in Medieval England (Pustilnik, 2003), a seemingly radical hypothesis dating from British astronomer William Herschel, who suggested a link between sunspots and wheat prices in 1801.
So, now we know that the more active sun warms the planet directly with increased incident radiation and indirectly both by reducing low cloud and likely by elevating the proportion of gaseous water -- the most important greenhouse gas.
This is precisely the kind of feedback hypothesized for enhanced greenhouse except this now has a demonstrated physical mechanism and is of such importance we should walk through its function just to be clear.
Increased solar activity acts directly on the Earth with a small increase in radiation, a small heating effect and an associated increase in evaporation. This same increase in activity suppresses cosmic ray penetration of Earth's atmosphere, thus reducing available low cloud condensation nuclei. This sequence of events increases clear sky and incoming radiation while increasing the already dominant clear sky greenhouse effect from gaseous water vapor.
The reverse effect of a more quiescent sun reduces direct solar warming and, by permitting the penetration of cosmic rays, facilitates low cloud formation, which increases reflection of already reduced solar radiation, reduces clear sky, reduces evaporation and simultaneously reduces the availability of the most important greenhouse gas, water vapor, through condensation and precipitation.
Thus solar activity has associated positive feedback when more active and negative feedback when less active, dramatically magnifying Earth's thermal response to changes in solar activity and explaining how fractions of Wm-2 change in direct solar radiation translate to many Wm-2 effect between positive and negative phases of relative solar activity.
Good cloud data is in short supply and covers only the recent decades but we can derive cosmic ray intensity and deduce there has been a general reduction in cloud cover during the 20th Century. While we are hesitant to extrapolate from very short data series (always a dubious procedure) it is entirely plausible that reduction in low cloud over the period could conservatively be estimated to have increased heating at Earth's surface by 5-10 Wm-2, an amount more than sufficient to account for all the estimated warming over the period.
Additionally, the mechanism described by Svensmark et al explains observed drought response to the recently more active sun and the reduction in cloudiness, probably coupled with snowfield discoloration from dust, soot and other particulates goes a long way toward explaining a disproportionate Arctic response, one apparently lacking in the Antarctic where such pigments are in relatively short supply, leaving snowfield albedo relatively unchanged.
This puts anthropogenic emissions in an interesting light. Since solar effects, both direct and indirect, are more than sufficient to account for net estimated temperature change over the period of significant fossil fuel usage, have humans been warming or cooling the planet? We know there are effects from land use change and we know we have added to atmospheric backscatter of solar radiation from particulates (sulfate aerosols, dust from agriculture...) but we are no longer certain of the net sign of anthropogenic temperature change.
The one thing we are reasonably sure of is that twiddling about with emissions of carbon dioxide will have no discernable effect on global mean temperature.
If you think the above is really quite significant in the "greenhouse debate" then you are right, which is probably why the mainstream media seem to have completely ignored it. The hazards of excessive investment in the enhanced greenhouse hypothesis, we suppose.
Looks like there's nothing new under the sun after all.
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