Our sun is a variable star and goes through cycles of high output and low output. An example of low output was the Maunder and Dalton Minima when severely colder temperatures were recorded in Europe, Asia, South America and Africa. We are currently in the Modern Maximum which began in 1914.
As the sun's output weakens, the magnetic field around it decays and this doesn't deflect charged cosmic rays as much. Here are some numbers from NASA:
Cosmic Rays Hit Space Age High
Planning a trip to Mars? Take plenty of shielding. According to sensors on NASA's ACE (Advanced Composition Explorer) spacecraft, galactic cosmic rays have just hit a Space Age high.
"In 2009, cosmic ray intensities have increased 19% beyond anything we've seen in the past 50 years," says Richard Mewaldt of Caltech. "The increase is significant, and it could mean we need to re-think how much radiation shielding astronauts take with them on deep-space missions."
The cause of the surge is solar minimum, a deep lull in solar activity that began around 2007 and continues today. Researchers have long known that cosmic rays go up when solar activity goes down. Right now solar activity is as weak as it has been in modern times, setting the stage for what Mewaldt calls "a perfect storm of cosmic rays."
"We're experiencing the deepest solar minimum in nearly a century," says Dean Pesnell of the Goddard Space Flight Center, "so it is no surprise that cosmic rays are at record levels for the Space Age."
So looking at 30-50 years minimum of significantly cooler weather. As more people die from cold than from heat, it is time for some rational decisions to be made and soon. I have firewood stacked up and a lot of trees on my property. City dwellers do not have that option.