Strengthening tropical Pacific zonal sea surface temperature gradient consistent with rising greenhouse gases

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As exemplified by El Nino, the tropical Pacific Ocean strongly influences regional climates and their variability worldwide1–3. It also regulates the rate of global temperature rise in response to rising GHGs4. The tropical Pacific Ocean response to rising GHGs impacts all of the world’s population. State-of-the-art climate models predict that rising GHGs reduce the west-to-east warm-to-cool sea surface temperature gradient across the equatorial Pacific5. In nature, however, the gradient has strengthened in recent decades as GHG concentrations have risen sharply5. This stark discrepancy between models and observations has troubled the climate research community for two decades. Here, by returning to the fundamental dynamics and thermodynamics of the tropical ocean–atmosphere system, and avoiding sources of model bias, we show that a parsimonious formulation of tropical Pacific dynamics yields a response that is consistent with observations and attributable to rising GHGs. We use the same dynamics to show that the erroneous warming in state-of-the-art models is a consequence of the cold bias of their equatorial cold tongues. The failure of state-of-the-art models to capture the correct response introduces critical error into their projections of climate change in the many regions sensitive to tropical Pacific sea surface temperatures. Observations of the tropical Pacific exhibit an increasing zonal sea surface temperature gradient, while climate models predict the opposite. This study shows that an increased gradient is consistent with greenhouse gas warming, and that climate model discrepancies arise from cold tongue biases.