What is with this confidence interval? I’m wondering what kind of uncertainty would result in an interval where potentially 10s of millions of lives are saved b

What is with this confidence interval? I’m wondering what kind of uncertainty would result in an interval where potentially 10s of millions of lives are saved by burning fossil fuels. “ We estimate a global total of 10.2 (95% CI: −47.1 to 17.0) million premature deaths annually attributable to the fossil-fuel component of PM2.5.”