A reader sent this abstract of a Henrik Svensmark study with a one word caption: Wow! I agree. The notion that "local" (and by local, we mean unimaginably far away) supernova affecting the Earth's climate is certainly creative. Haven't even read the thing so certainly not buying it yet, but it certainly is an amazing hypothesis.
Observations of open star clusters in the solar neighbourhood are used to calculate local supernova (SN) rates for the past 510 Myr. Peaks in the SN rates match passages of the Sun through periods of locally increased cluster formation which could be caused by spiral arms of the Galaxy. A statistical analysis indicates that the Solar system has experienced many large short-term increases in the flux of Galactic cosmic rays (GCR) from nearby SNe. The hypothesis that a high GCR flux should coincide with cold conditions on the Earth is borne out by comparing the general geological record of climate over the past 510 Myr with the fluctuating local SN rates. Surprisingly, a simple combination of tectonics (long-term changes in sea level) and astrophysical activity (SN rates) largely accounts for the observed variations in marine biodiversity over the past 510 Myr. An inverse correspondence between SN rates and carbon dioxide (CO2) levels is discussed in terms of a possible drawdown of CO2 by enhanced bio-productivity in oceans that are better fertilized in cold conditions – a hypothesis that is not contradicted by data on the relative abundance of the heavy isotope of carbon, 13C.
I was initially very skeptical of Svensmark's work attempting to link cosmic rays to cloud formation, with that affect acting as an amplifier (in terms of warming and cooling effects) of changes in solar output. I must say that over time, that work has survived replication effects pretty well.