Response of climate to solar forcing recorded in a 6000-year
Previous studies have shown that the oxygen isotope ratio (δ18O) of plant cellulose can serve as a sensitive proxy indicator of past climate, but its application has mainly been restricted to tree-rings. Here we present a 6000-year high-resolutionδ18O record of peat plant cellulose from northeastern China. Theδ18O variation is interpreted as reflecting changes in regional surface air temperature. The climate events inferred from the isotope data agree well with archaeological and historic evidence. The record shows a striking corre spondence of climate events to nearly all of the apparent solar activity changes characterized by the atmospheric radiocarbon in tree-rings over the past 6000 years.
Spectral analysis of theδ18O record reveals the periodicities of around 86, 93, 101, 110, 127, 132, 140, 155, 207, 245, 311, 590, 820 and 1046 years, which are similar to those detected in the solar excursions. We consider these observations as further evidence for a close relationship between solar activity and climate variations on timescales of decades to centuries. Our results also have implications for distinguishing between natural and anthropogenic contributions to future climate change.
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Role Of Solar Radiation In Climate Change
Decrease in solar radiation discovered
The initial findings, which revealed that solar radiation at the Earth’s surface is not constant over time but rather varies considerably over decades, were published in the late 1980s and early 1990s for specific regions of the Earth. Atsumu Ohmura, emeritus professor at ETH Zurich, for example, discovered at the time that the amount of solar radiation over Europe decreased considerably between the 1950s and the 1980s. It wasn’t until 1998 that the first global study was conducted for larger areas, like the continents Africa, Asia, North America and Europe for instance. The results showed that on average the surface solar radiation decreased by two percent per decade between the 1950s and 1990.
In analyzing more recently compiled data, however, Wild and his team discovered that solar radiation has gradually been increasing again since 1985. In a paper published in “Science” in 2005, they coined the phrase “global brightening” to describe this new trend and to oppose to the term “global dimming” used since 2001 for the previously established decrease in solar radiation.
Only recently, an article in the journal Nature, which Wild was also involved in, brought additional attention to the topic of global dimming/brightening.
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It is particularly unclear as to whether it is the clouds or the aerosols that trigger global dimming/brightening, or even interactions between clouds and aerosols, as aerosols can influence the “brightness” and lifetime of the clouds. The investigation of these relations is complicated by the fact that insufficient – if any – observational data are available on how clouds and aerosol loadings have been changing over the past decades. The recently launched satellite measurement programs should help to close this gap for the future from space, however.
“There is still an enormous amount of research to be done as many questions are still open”, explains Wild. This includes the magnitude of the dimming and brightening effects on a global level and how greatly the effects differ between urban and rural areas, where fewer aerosols are released into the atmosphere. Another unresolved question is what happens over the oceans, as barely any measurement data are available from these areas.
A further challenge for the researchers is to incorporate the effects of global dimming/brightening more effectively in climate models, to understand their impact on climate change better. After all, studies indicate that global dimming masked the actual temperature rise – and therefore climate change – until well into the 1980s. Moreover, the studies published also show that the models used in the Intergovernmental Panel on Climate Change’s (IPCC) fourth Assessment Report do not reproduce global dimming/brightening adequately: neither the dimming nor the subsequent brightening is simulated realistically by the models. According to the scientists, this is probably due to the fact that the processes causing global dimming/brightening were not taken into account adequately and that the historical anthropogenic emissions used as model input are afflicted with considerable uncertainties.
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Solar Radiation and Climate Experiment (SORCE) Fact Sheet : Feature Articles
The launch of the Nimbus-7 satellite in 1978 changed all that. It enabled us for the first time to detect sunlight without interference from the atmosphere. The Earth Radiation Budget (ERB) instrument on the satellite measured levels of solar radiation just before it strikes the Earth’s atmsophere. Through subsequent satellite missions, scientists have gathered a wealth of information on the Sun and the solar energy that drives our world’s climate system.
Today researchers know that roughly 1,368 watts per square meter (W/m2) of solar energy on average illuminates the outermost atmosphere of the Earth. They know that the Earth absorbs about only 70 percent of this total solar irradiance (TSI), and the rest is reflected into space. Perhaps most intriguing, researchers have affirmed that the TSI doesn’t stay constant, but varies slightly with sunspots and solar weather activity. In particular, by analyzing satellite data, scientists have observed a correlation between the Sun’s output of energy and the 11-year sunspot cycle, which physicists have known of since Galileo’s time. These data show that TSI varies just as regularly as the sunspot activity over this 11-year period, rising and falling 1.4 W/m2 through the course of the cycle (0.1 percent of the TSI). There are also longer-term trends in solar weather activity that last anywhere from years to centuries to millennia and may have an impact on global warming.
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In 2003, Earth scientists will move a step closer to a full understanding of the Sun’s energy output with the launch of the Solar Radiation and Climate Experiment (SORCE) satellite. SORCE will be equipped with four instruments that will measure variations in solar radiation much more accurately than anything now in use and observe some of the spectral properties of solar radiation for the first time. Robert Cahalan of NASA Goddard Space Flight Center serves as SORCE Project Scientist, and the four instruments are being built at the University of Colorado under the direction of Gary Rottman, SORCE Principal Investigator, with participation by an international team of scientists. SORCE will be launched in January 2003 from Kennedy Space Center on a Pegasus XL launch vehicle provided by Orbital Sciences Corporation. With data from NASA’s SORCE mission, researchers should be able to follow how the Sun affects our climate now and in the future.
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What I SHOULD HAVE WRITTEN, solar radiation has not increased, but rather, in addition to the 11 year cycles, which I knew about, solar dimming has affected climate, which is known.
It turns out, the sun has dimmed, by 2% per decade, since 1950, and it started brightening, in 1985. Since temperatures are rising steadily, the principal forcing factor for long-term rises AND falls in Earth's average temperature is still CO2, while out-gassing of methane is the leading runaway-rise forcing factor, which will do more damage, during times of brightening, either in the long-term or short-term bright periods.
But solar radiation has still been consistent, even if my former statement was inaccurate. The fact remains, long-term climate change is occurring, relative to increasing GHG concentrations in the atmosphere. Action must be taken, to reverse forcing factors, via reducing variable GHG emissions, while increasing metabolization, of CO2. Temperatures will continue to increase.
The sun isn't the main forcing factor, in modern, long-term climate change, Fatass. Temperature rise has been steady, and it is accelerating, during 2% brightness per decade increase or decrease, of course, more during bright periods, see Trakar's relevant hockey sticks:
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