We have discussed recent increases in heavy precipitation events in the Northeast and multiple scientific assessment reports have concluded that these increases are likely due to human-induced climate warming. However, is it possible that there is another contributing factor especially as warming has slowed some in the last decade?
New research published recently in the peer-reviewed journal Geophysical Research Letters presents evidence to suggest that the solar cycle plays a significant role in precipitation fluctuations in the Northeast U.S.
A pair of researchers (Jonathan Nichols from Columbia University and Yongsong Huang from Brown University) analyzed an impressive 6800-year hydrogen isotope record from the Great Heath, a peatland in coastal Maine. They discovered a significant correlation between solar variations (high/low solar irradiance) and wet/dry periods in the Northeast.
Wet periods correlated with low solar periods and dry periods with higher solar activity. In order to double-check their work, the researchers compared the peat-derived data against carbon-dated paleo-shorelines for nearby ponds as well as against other reconstructed datasets from Europe.
While everyone agrees that the sun plays a major role in our climate, many in the climate change research community believe that relatively small changes in solar irradiance are insufficient to drive significant, big-picture climate change. Indeed, the 2007 IPCC report stated that solar forcing was much too small to counteract the effect from human-introduced greenhouse gases.
But these two researchers argue that secondary impacts, like the theorized connection between low solar periods and enhanced negative states of the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) - linked to very cold, snow weather over eastern North America (and western Europe) - could cause significant regional impacts.
In their research, they note that reconstructed models link the Medieval Climate Anomaly (sometimes referred to as the Medieval Warm Period, from the 9th to 13th centuries) with high solar irradiance and a positive NAO (warmth in eastern North America, western Europe). They link the Little Ice Age (from the 16th-mid 19th century period) with a very negative NAO and low solar irradiance.
The researchers believe their study offers the “strongest evidence for solar impact on the hydrologic cycle in the northeastern U.S.” as the “AO/NAO system is critical to amplifying the weak solar signal”.
The authors conclude:
Currently, the Sun may be entering another Maunder-like “grand minimum” in activity as has occurred several times during past millennia It is possible that effects of this change in solar irradiance will be felt more strongly in regions particularly sensitive to such amplifying mechanisms, such as the Northeastern US, and may result in increased cool season precipitation, of particular interest in light of recent spring flooding.
Generally, the climate change community places less emphasis on solar forcing compared to greenhouse gases. Risks from human-induced climate change itself arise not merely from the quantity of gases released, but all the assumed positive feedbacks that amplify the impacts and accelerate the changes.
So why not entertain the notion that adjustments in solar irradiance could also trigger feedback mechanisms to amplify its impact?
The 2009 and 2010 record –NAO and –AO winters (and record East Coast snowfalls) just happened to coincide with the quietest solar cycle in over 100 years. This would seem to support this paper’s research (along with the precipitation increase in recent years).
In addition- and this could be an alternative explanation for the researcher’s solar-hydro correlation- a research group at CERN (the European Organization for Nuclear Research) is working on understanding the impact of cosmic rays on our atmosphere via an experiment known as CLOUD (Cosmis Leaving OUtdoor Droplets). We know for a fact that when the sun gets quieter, more cosmic rays bombard our planet. Cosmic ray particles may help create more cloud condensation nuclei. Quiet solar periods would therefore lead to more clouds and more precipitation.
A blog on the website RealClimate, however, cautions: ...it is clear that substantially more work needs to be done before we adequately understand these physical connections, and that no broad conclusions regarding the effect of cosmic rays on clouds and climate can (or should) be drawn from the first round of CLOUD results
As such, precipitation and cosmic ray research is far from complete, but an active area of inquiry...