Using individual-level data on more than 37.1 million births, we find that exposure to extreme hot temperatures during pregnancy leads to lower birth weight. We combine this finding with estimates of the distribution of future daily temperatures from state-of-the-art climate change predictions. We then use these predictions of the effect of climate change on the distribution of daily temperatures to estimate the predicted effect of global climate change on future birth weights by the end of the century. These estimates imply that mean birth weights will decrease on average by 0.22 percent (7.5 grams) among whites and by 0.36 percent (11.5 grams) for blacks by the end of the century. Further, the impact is not spread evenly through the birth weight distribution. We find an estimated 5.9 percent increase in the probability of a low birth weight birth (defined as less than 2,500 grams) for whites and a 5.0 percent increase for blacks.