Yet, sunspots are easy to see, even without a telescope. More than likely it's because there were very few sunspots during this period. Even small changes in the energy output of the Sun can change the climate on the Earth. But other objects in space can have an affect as well. As popularized by a couple of recent movies, let's consider comets.
Comets are essentially dirtly iceballs.
These objects have highly eccentric orbits. Most of the life of a comet is spent moving very slowly in the regions far beyond Pluto. But occasionally, one will enter the solar system. According to Kepler's 2nd law, the comet will pick up speed. Hence, if it comes into the inner part of the solar system, it won't stay here for long.