One of the hot topics, so to speak, in the global warming debate is allocating responsibility for 20th century warming between natural and man-made effects. This is harder than one might imagine â after all, no oneâs thermometer has two readings, one for ânaturalâ and one for âman-made.â This week, from CERN in Geneva, comes an important new study in this debate.
Global warming skeptics argue that only a portion, possibly a small portion, of recent warming is due to man-made CO2 and greenhouse gasses. Climate alarmists have, in turn, argued that all of 20th century warming, and more, was due to anthropogenic effects (if the âand moreâ is confusing, it means that some scientists believe that certain man-made and natural cooling effects actually reduced man-made warming below what it might have been.)
It is only in this context that Michael Mannâs famous hockey stick studies make even a bit of sense. After all, what do pre-industrial world temperature trends have anything to tell us about the effect of man-made Co2 on 20th century temperatures?
But Mannâs work had a very specific purpose â to make the case that the natural variability of temperatures, at least on a millennial scale, is very small. Though considered by many to be deeply flawed, Mannâs work seemed to say that the anecdotal historical record was wrong, that there was not a Medieval warm period or very cold period during the solar minima of the 17th and 18th centuries. In his hockey stick, the only significant trend in temperatures began with the industrial age, and manâs production of CO2.
Much of the debate revolves around the role of the sun, and though holding opposing positions, both skeptics and alarmists have had good points in the debate. Skeptics have argued that it is absurd to downplay the role of the sun, as it is the energy source driving the entire climate system. Michael Mann notwithstanding, there is good evidence that unusually cold periods have been recorded in times of reduced solar activity, and that the warming of the second half of the 20th century has coincided with a series of unusually strong solar cycles.
Global warming advocates have responded, in turn, that while the sun has indeed been more active in the last half of the century, the actual percentage change in solar irradiance is tiny, and hardly seems large enough to explain measured increases in temperatures and ocean heat content.
And thus the debate stood, until a Danish scientist named Henrik Svensmark suggested something outrageous â that cosmic rays might seed cloud formation. The implications, if true, had potentially enormous implications for the debate about natural causes of warming.
When the sun is very active, it can be thought of as pushing away cosmic rays from the Earth, reducing their incidence. When the sun is less active, we see more cosmic rays. This is fairly well understood. But if Svensmark was correct, it would mean that periods of high solar output should coincide with reduced cloud formation (due to reduced cosmic ray incidence), which in turn would have a warming effect on the Earth, since less sunlight would be reflected back into space by clouds.
Here was a theory, then, that would increase the theoretical impact on climate of an active sun, and better explain why solar irradiance changes might be underestimating the effect of solar output changes on climate and temperatures.
Skeptics, of course, immediately jumped on the Svensmark bandwagon, though some of the more careful of us observed that it was silly to criticize the gaps in anthropogenic global warming theory only to go haring off after a theory that was even less understood.
Since he first suggested his hypothesis over a decade and a half ago, Svensmark and other researchers have slowly been putting together research to test it. Svensmark conducted some early cloud chamber laboratory studies that seemed to show a correlation between cloud seeding and cosmic rays. A few ground studies have been conducted trying to correlate clouds with cosmic rays, and a few months ago Roy Spencer showed data from the CERES satellite
that suggested a pretty good correlation between cosmic ray incidence and reflected solar radiation (increased cloud formation would cause increases in such reflected radiation).
For quite a while, the climate community (at least the skeptic side) has been eagerly awaiting the results from a study group named CLOUD at CERN in Geneva. In their sophisticated cloud chamber, they undertook to duplicate the chemistry of the upper atmosphere, and then stimulate the chamber with simulated cosmic rays from a particle accelerator.
About a month ago, before the study results had been made public, the skeptic camp experienced a âdog that didnât barkâ moment when the director of CERN asked that his scientists (incredibly) refrain from drawing any public conclusions from the study, saying âI have asked the colleagues to present the results clearly, but not to interpret them.â Skeptics, lincluding me
, guessed that this meant the data was tending to support the Svensmark hypothesis. After all, the climate community has no problem drawing alarmist conclusions from the thinnest of data. Every climate scientist seems to have his or her own full-time PR agent. If they were explicitly avoiding public comment, and in fact telling scientists to effectively not do their job and draw no conclusions from the data, then the results must be threatening to the mainstream global warming community.
And indeed they appear to be just that.
In a paper to be released today in Nature, the data tells a clear story. Scientists found that when shielding was removed and natural cosmic rays allowed to hit the chamber, cloud seeding increased dramatically, and it increased substantially again when additional artificial cosmic rays were added. Svensmark appears to have gotten it right.
But letâs be careful. We are basically now in the exact same place with Svensmark that we are with CO2 greenhouse warming. We know the relevant effects exist in a lab, and are fairly certain they exist in nature, but we are uncertain how sensitive the actual climate is to these effects. We skeptics criticize alarmists for exaggerating feedbacks and real-world sensitivities to CO2
. We should avoid the same mistake.
But for now, I am going to forget about the climate debate for a moment and just experience the joy that comes from finding out something new and surprising about how the world works. Hereâs to unknown men who come up with crazy, counter-intuitive notions at the faculty lunch table âŠ and turn out to be right.