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Land-surface cooling and global cooling follow different energy paths

A peer-reviewed climate-model study found that changes in evaporation can cool a land surface without removing an equivalent amount of energy from the Earth system. In idealized simulations, global temperature tracked radiative shifts across the atmosphere’s outer boundary more closely. Cloud responses and the latitude of the intervention altered the result.

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Low cumulus clouds cast shadows across a continuous landscape of sunlit meadows and mature woodland.

Evaporation cools the surface by moving heat

A single peer-reviewed simulation study examined why cooling a land surface and cooling the planet can have different outcomes. Philipp de Vrese and colleagues used MPI-ESM, an Earth-system model, to change surface reflectivity and the water available for evaporation separately. The experiments began with preindustrial conditions and compared large latitude bands.[1]

More evaporation moved heat from the surface into the atmosphere and cooled the ground locally. That energy transfer did not remove an equivalent amount of heat from the Earth system. The study compared this redistribution with changes in radiation crossing the top of the atmosphere.[1]

Global temperature tracks changes in radiation

Over the 50-year evaluation, the global mean temperature response was more closely related to net incoming shortwave radiation across the atmosphere’s outer boundary. The modeled temperature response was approximately 0.4 kelvin for each watt per square metre of radiative change. Carbon dioxide concentrations were prescribed, excluding feedbacks from vegetation’s carbon exchange.[1]

Clouds change the response across latitudes

Cloud formation altered how surface reflectivity translated into planetary reflectivity. Middle- and higher-latitude cloud responses were important, while tropical interventions behaved differently. The experiments represented idealized changes rather than a particular irrigation or afforestation project; their results depend on the atmospheric and cloud components of one climate model.[1]

References

  1. News sourceNature CommunicationsRadiative balance governs land-surface changes’ global temperature effect
    Primary paperNature CommunicationsGlobal climate impact of land-surface change driven by radiative effects
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Space and explorationEnergy transition and climate

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