Global-scale changes in Earth’s energy budget and implications for the water cycle

The climate system is heating up, causing warming at the surface and changes in the global water cycle. Updated reconstructions of Earth’s energy budget since the 1980s are presented and show how heat uptake is unevenly distributed across the northern and southern hemisphere. Heating is closely associated with ocean heat content changes and sea level rise while surface warming depends on partitioning between the upper mixed layer and deeper levels, leading to decadal variability. CMIP6 simulations are used to illustrate how global precipitation and evaporation are constrained by the Earth's energy balance to increase at ∼2–3%/°C and how this rate of increase is suppressed by rapid atmospheric adjustments in response to greenhouse gases and absorbing aerosols that directly alter the atmospheric energy budget. Rapid adjustments to forcings, cooling effects from scattering aerosol, and observational uncertainty can explain why observed global precipitation responses are currently difficult to detect but are expected to emerge and accelerate as warming increases and aerosol forcing diminishes.