A new study warns that catastrophic effects of global warming could cause the worldwide economy to shrink by about 20% by the middle of the century, even if future emissions of greenhouse gases are drastically reduced. If emissions aren’t reduced, even greater economic damage can be expected, according to researchers at the Potsdam Institute for Climate Impact Research (PIK) in Germany. The study, published on Wednesday in the journal Nature, calculated annual economic damage from climate change at more than $38 trillion per year if climate-damaging emissions aren’t significantly reduced. That…