Vulgar political machinations often obscure interesting and relevant concepts about climate forcings.

The total energy reaching Earth from the Sun varies by only 0.1 percent across the solar cycle. Scientists have sought for decades to link these ups and downs to natural weather and climate variations and distinguish their subtle effects from the larger pattern of human-caused global warming.

Building on previous work, NCAR researchers used computer models of global climate and more than a century of ocean temperature data to answer longstanding questions about the connection between solar activity and global climate. Changes in greenhouse gases were also included in the model, but the main focus of the study is to examine the role of solar variability in climate change. . .

The new paper, along with an earlier one by Meehl and colleagues, shows that as the Sun reaches maximum activity, it heats cloud-free parts of the Pacific Ocean enough to increase evaporation, intensify tropical rainfall and the trade winds, and cool the eastern tropical Pacific. The result of this chain of events is similar to a La Nina event, although the cooling of about 1-2 degrees Fahrenheit is focused further east and is only about half as strong as for a typical La Nina. Over the following year or two, the La Nina-like pattern triggered by the solar maximum tends to evolve into an El Nino-like pattern, as slow-moving currents replace the cool water over the eastern tropical Pacific with warmer-than-usual water. Again, the ocean response is only about half as strong as with El Nino. . .

Scientists have known for years that long-term solar variations affect certain weather patterns, including droughts and regional temperatures. But establishing a physical connection between the decadal solar cycle and global climate patterns has proven elusive. One reason is that only in recent years have computer models been able to realistically simulate the processes underlying tropical Pacific warming and cooling associated with El Nino and La Nina. With those models now in hand, scientists can reproduce the last century's solar behavior and see how it affects the Pacific. . .

Although this Pacific pattern is produced by the solar maximum, the authors found that its switch to an El Nino-like state is likely triggered by the same kind of processes that normally lead from La Nina to El Nino. The transition starts when changes in the strength of the trade winds produce slow-moving off-equatorial pulses known as Rossby waves in the upper ocean, which take about a year to travel back west across the Pacific.

The energy then reflects from the western boundary of the tropical Pacific and ricochets eastward along the equator, deepening the upper layer of water and warming the ocean surface. As a result, the Pacific experiences an El Nino-like event about two years after solar maximum. The event settles down after about a year, and the system returns to a neutral state.

"El Nino and La Nina seem to have their own separate mechanisms," says Meehl, "but the solar maximum can come along and tilt the probabilities toward a weak La Nina. If the system were heading toward a La Nina anyway," he adds, "it would presumably be a larger one."

My emphasis. Political arguments usually focus on the gross magnitude of changes - the Sun varies by only 0.1 percent across the solar cycle - to dismiss solar variation as an important issue, contra sceptical arguments which seek to dismiss GHG forcing since anthropogenic sources are a tiny percent of all the GHGs produced naturally. But these tiny variations do matter, and their effects can be amplified when they coincide with other cyclical changes. The one mentioned - a La Nina-like pattern triggered by the solar maximum amplifying a true La Nina - is one of many such potentially reinforcing or damping oscillations. The PDO is one that is often considered in the Pacific and there are also oscillations in the Atlantic of both ocean currents and atmospheric streams. Sometimes they counter one another and sometimes they reinforce one another since they have different periods of oscillation. Pacific and Atlantic cycles also interact with one another across the N. American continent. It's complicated. Seemingly unexplainable events such as one hundred or even five hundred year droughts and floods are the result of all of the various cycles coinciding and amplifying one another, a concordance that seldom but inevitably repeats.

We may not be able to do anything about such complex events, but being able to anticipate them may help us better cope with them. Stockpile food and fuel. Winter is coming, or the reverse.