On the face of it, it is impossible. Cosmic rays vary over time, and climate varies over time, and the two variations do not correspond. Global temperature has been going up over the last century, in correspondence with increased of atmospheric CO2, and this makes sense because the physics says that CO2 is a greenhouse gas, and this whole global warming thing is a greenhouse effect. Bringing cosmic rays into the situation seems both unnecessary and difficult to do.
But it turns out that there is a cosmic ray – climate connection which is interesting if it turns out to be true. But this connection is NOT any kind of link between cosmic rays and global warming. Cosmic rays do not cause global warming. Did you read that last sentence? OK, good.
It turns out that cosmic rays may play a role in how particles of stuff cause the aggregation of water vapor into droplets. However, this effect is not entirely clear and seems to only work on some kinds of particles, and there is zero. Zero. (did you read that part where I said “zero”?) correlation between amounts of cosmic rays and anything at all related to climate.
Zero, nada, zilch, nothing, kitu haiko.
Global warming denialists, however, that they would like to do more damage to our public understanding of science than they already have by breathlessly connecting this recent interesting research on cosmic rays and more earthly substances to global climate change to the exclusion of that which we know is real.
Moth Eyes has a nice write-up on this and a few nice graphs as well.