Solar Radiation, Co2, and Global Climate

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One reason that it is important to understand the role of solar radiation in climate change is because the effect of CO2 mitigation will not be continuous. Removing a few tons of CO2 from the atmosphere will remove its greenhouse gas warming effect, but it will also slightly reduce the ability of the atmosphere to block radiation. For this reason, while people might be expecting a certain continual decrease of global temperatures due to expenditure on CO2 mitigation, the actual climatic effect is logarithmic, with additional temperature decreases requiring more and more CO2 reduction.

Variations in solar brightness are not, however, enough to explain global warming on their own. As previously stated, the fluctuations in solar radiation are extremely low, and the amount of that radiation that reaches the earth’s surface has remained relatively constant throughout the earth’s history. The cycles of solar radiation and the cycle of global temperatures do not appear to be in sync, and most atmospheric researchers believe that the effects of the sun’s fluctuations is minimal when compared to other possible causes of climate change. According to a spokesperson of the National Center of Atmospheric Research, “Our results imply that, over the past century, climate change due to human influences must far outweigh the effects of changes in the Sun's brightness.” (Foukal, 2006)

During periods of global dimming, such as the period that is upcoming (if the current theory about global sunspot cycles is correct) scientists found that light is more scattered by increased aerosols and cloud cover, leading plants to increase CO2 at a more efficient rate than when the air is clean and clear. According to an article in the journal Nature, “this is because scattered light penetrates deeper into the vegetation canopy than direct sunlight which means the plants can use the light more effectively for photosynthesis. Consequently there was 10 percent more carbon stored in the terrestrial biosphere between 1960 and 1999.” (ETH Zuric, 2009)

While we can measure global dimming and brightening, and most scientists are reasonably certain that it exists, there is no obvious consensus on its cause. It is possible that the clouds play a role in triggering global dimming, and this in turn would imply that aerosols in the atmosphere play a foundational role in solar radiation moderation and thus climate control. (ETH Zuric, 2009) There is a gap in the amount of data available for some of these changes, as it was only recently that satellites began providing comprehensive data coverage of the entire globe.

Does the sun actually change the amount of radiation that it outputs over time? As stated previously, this is extremely unlikely. The amount of solar radiation that the sun generates is virtually a constant under anything but the most extreme timeline, and astronomers believe that the levels of radiation do not fluctuate except on a cyclical level. “There is no plausible physical cause for long-term changes in solar brightness other than changes caused by sunspots and faculae,” says P. Foukal in Nature. (Foukal, 2006)

In conclusion, there are measurable changes in solar radiation at the earth’s surface and at the earth’s outer atmospheric edge. The sun varies slightly in its solar output throughout an 11 year solar cycle, and the earth’s atmosphere causes additional variations in solar radiation due to the different reflective and trapping capabilities of gases, particulates, and aerosols. Solar radiation variance at the earth’s surface can be directly impacted by the removal or addition of greenhouse gases to the atmosphere, with the net effect of greenhouse gas reduction being muted by the warming capabilities of solar energy

Work Cited

ETH Zuric. (2009, August 11). Role of Solar Radiation in Climate Change. ScienceDaily.

Foukal, P. (2006). Variations in Solar Luminosity and their Effect on the Earth's Climate. Nature.

Haigh, J. (2010). An Influence of Solar Spectral Variations on Radiative Forcing of Climate. Nature, 696-699.

Haywood, J. (2011). The Roles of Aerosol, Water Vapor and Cloud in Future Global Dimming/Brightening. Journal of Geophysical Research: Atmospheres, 1900-1943.

Lean, J. (2000). Evolution of the Sun's Spectral Irradiance Since the Maunder Minimum. Geophycial Research Letters, 2425-2428.

NASA Earth Observatory. (n.d.). Solar Radiation and Climate Experiment. Retrieved December 3, 2013, from The Sun and Global Warming: http://earthobservatory.nasa.gov/Features/SORCE/sorce_04.php