Only in the past decade of so have two technologies (high-volume hydraulic fracturing and precision directional drilling) combined to allow extracting natural gas from shale, and half of all shale gas ever developed has been produced only in the past 3-4 years. Consequently, the scientific study of the environmental consequences is also quite new. Nonetheless, these consequences are large and diverse, including contaminating groundwater and surface waters and polluting the air. One of the greatest concerns is with the climatic effects: shale gas is widely promoted as a bridge fuel that allows society to continue to rely on fossil fuels while reducing greenhouse gas emissions. However, my research with Prof. Ingraffea indicates that when emissions of methane as well as carbon dioxide are considered, shale gas has perhaps the largest greenhouse gas footprint of any fossil fuel. Even before the shale gas boom, the natural gas industry was the largest source of methane pollution in the US and one of the two largest sources globally (together with animal agriculture). Without large reductions in emissions of both methane and carbon dioxide, the average temperature of the Earth will reach 1.5°C to 2°C above the 20th Century baseline within the next few decades, creating a risk of runaway feedbacks in the climate system leading to even more rapid warming and climate disruption. To reduce this risk, society should move away from all fossil fuels – but particularly shale gas – as rapidly as possible.