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The carbon intensity of U.S. output has experienced a secular decline in recent decades. Using an agnostic identification approach we show that news about future total factor productivity explain the bulk of longrun variation in emission intensity. News about green technologies give rise to similar dynamics. Both innovations precede a persistent increase of output and TFP. Yet, they are associated with only a temporary decline of emissions, followed by a hump-shaped rebound. New technologies have thus been a key driver of growth in recent decades but have not permanently reduced emissions. We discuss the Economic underpinnings of this rebound effect.