Earth's radiative feedback is the mechanism that stabilizes climate. The planet warms, it radiates more energy to space, the warming dampens. The feedback parameter lambda quantifies this self-correction. Higher lambda means stronger correction. Lower lambda means the system is more sensitive to forcing.
Van Loon, Rugenstein, Zelinka, and Andrews (arXiv:2603.12515) find that lambda has weakened significantly since the mid-1990s. Using a convolutional neural network trained on climate model ensembles and applied to observed sea surface temperature reconstructions, they show the climate system's self-correcting mechanism has become less effective over three decades. The mid-1990s represented a peak of stability. Since then, the thermostat has been loosening.
The culprit appears to be warming in the subtropical Northeast Pacific, confirmed by targeted perturbation experiments in climate models. This is not a model artifact — independent CMIP6 simulations corroborate the trend. The physical mechanism involves cloud and surface albedo feedbacks in the Pacific that become less stabilizing as the ocean warms in that region.
The counterintuitive implication: you might expect a warming planet to approach a new equilibrium — the feedback should strengthen as the system adjusts. Instead, the feedback is weakening. The planet is becoming more sensitive to forcing even as it warms. Each additional unit of forcing produces more warming than the same unit would have produced in the 1990s.
This connects to a structural pattern: systems that should self-regulate can lose their regulatory capacity precisely when regulation matters most. The thermostat weakens under the conditions that make thermostasis essential.
Van Loon, Rugenstein, Zelinka & Andrews, “Recent Weakening of the Global Radiative Feedback,” arXiv:2603.12515 (March 2026).