A drier than expected future, supported by near-surface relative humidity observations

Despite continuous progress in climate modeling, global projections of the terrestrial water cycle remain highly model dependent. Here, we use quality-controlled gridded observations of temperature and humidity to constrain projected changes in continental near-surface relative humidity across the 21st century. Results show that the projections are poorly constrained when using surface temperature observations only and argue for mitigation policies that are not only rooted in global warming levels. Projections constrained with both near-surface temperature and relative humidity observations show an inevitable continental drying, especially in the northern midlatitudes where anthropogenic aerosols have, however, countered this long-term response until the late 1980s. A strong drying storyline is then used to highlight the urgent need for careful adaptation strategies and to suggest a possible contribution of land surface processes to model uncertainties.

Automated summary

Despite improvements in climate modeling, global predictions of the terrestrial water cycle remain uncertain. A study using observed data on temperature and humidity suggests that projections are more accurate when both factors are considered, and highlights the urgent need for mitigation policies. The study also identifies a drying trend in the future, particularly in the northern midlatitudes, and emphasizes the importance of adapting to these changes.