* Astronomy

There's been continual speculation about the connection between the Earth's climate and the local Galactic environment, along with the implications for life. Two researchers have explored any such link in more quantitative detail than in the past.

Ice Age Epochs and the Sun's Path through the Galaxy
Authors: D. R. Gies and J. W. Helsel
"We present a calculation of the Sun's motion through the Milky Way Galaxy over the last 500 million years. The integration is based upon estimates of the Sun's current position and speed from measurements with Hipparcos and upon a realistic model for the Galactic gravitational potential. We estimate the times of the Sun's past spiral arm crossings for a range in assumed values of the spiral pattern angular speed. We find that for a difference between the mean solar and pattern speed of Omega_Sun -Omega_p = 11.9 +/- 0.7 km/s/kpc the Sun has traversed four spiral arms at times that appear to correspond well with long duration cold periods on Earth. This supports the idea that extended exposure to the higher cosmic ray flux associated with spiral arms can lead to increased cloud cover and long ice age epochs on Earth. "
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An interaction with another star system will be gravitational. That could affect the Earth's climate by altering its orbit. However, given that the Earth's orbit is nearly circular, it seems that the solar systems has not been perturbed greatly by any passing star.
(though there may be perturbations on the Oort cloud and increased asteroid impacts)
On the other hand, as the solar system passes through a molecular cloud, there should be essentially no impact on the orbits of the planets, but the change in the local "environment" could have an influence on the Earth's climate.

For a difference between the mean solar and pattern speed of Omega_Sun - Omega_p = 11.9 +/- 0.7 km/s/kpc the Sun would traverse four spiral arms at times that appear to correspond well with long duration cold periods on Earth.