Natural variability alone does not account for observed changes in global (ocean and land) precipitation; rather, those changes have been directly affected by human activities new research shows.
Manmade increases in greenhouse gases and stratospheric ozone depletion are expected to lead to both increasing temperatures and redistribution of global precipitation.
It is rare for intensification and poleward shifts of precipitation to occur naturally, so this suggests strong evidence that humans are affecting global precipitation.
Read more at Lawrence Livermore National Laboratory