Understanding decreases in land relative humidity with global warming: Conceptual model and GCM simulations
Climate models simulate a strong land–ocean contrast in the response of near-surface relative humidity to global warming; relative humidity tends to increase slightly over oceans but decrease substantially over land. Surface energy balance arguments have been used to understand the response over oce...
| Main Authors: | , |
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| Format: | Journal article |
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American Meteorological Society
2016
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| _version_ | 1797054482619564032 |
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| author | Byrne, M O'Gorman, P |
| author_facet | Byrne, M O'Gorman, P |
| author_sort | Byrne, M |
| collection | OXFORD |
| description | Climate models simulate a strong land–ocean contrast in the response of near-surface relative humidity to global warming; relative humidity tends to increase slightly over oceans but decrease substantially over land. Surface energy balance arguments have been used to understand the response over ocean but are difficult to apply over more complex land surfaces. Here, a conceptual box model is introduced, involving atmospheric moisture transport between the land and ocean and surface evapotranspiration, to investigate the decreases in land relative humidity as the climate warms. The box model is applied to simulations with idealized and full-complexity (CMIP5) general circulation models, and it is found to capture many of the features of the simulated changes in land humidity. The simplest version of the box model gives equal fractional increases in specific humidity over land and ocean. This relationship implies a decrease in land relative humidity given the greater warming over land than ocean and modest changes in ocean relative humidity, consistent with a mechanism proposed previously. When evapotranspiration is included, it is found to be of secondary importance compared to ocean moisture transport for the increase in land specific humidity, but it plays an important role for the decrease in land relative humidity. For the case of a moisture forcing over land, such as from stomatal closure, the response of land relative humidity is strongly amplified by the induced change in land surface–air temperature, and this amplification is quantified using a theory for the link between land and ocean temperatures. |
| first_indexed | 2024-03-06T18:57:51Z |
| format | Journal article |
| id | oxford-uuid:1278fac0-ad65-456d-aebb-6f68472b3f2e |
| institution | University of Oxford |
| last_indexed | 2024-03-06T18:57:51Z |
| publishDate | 2016 |
| publisher | American Meteorological Society |
| record_format | dspace |
| spelling | oxford-uuid:1278fac0-ad65-456d-aebb-6f68472b3f2e2022-03-26T10:08:10ZUnderstanding decreases in land relative humidity with global warming: Conceptual model and GCM simulationsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:1278fac0-ad65-456d-aebb-6f68472b3f2eSymplectic Elements at OxfordAmerican Meteorological Society2016Byrne, MO'Gorman, PClimate models simulate a strong land–ocean contrast in the response of near-surface relative humidity to global warming; relative humidity tends to increase slightly over oceans but decrease substantially over land. Surface energy balance arguments have been used to understand the response over ocean but are difficult to apply over more complex land surfaces. Here, a conceptual box model is introduced, involving atmospheric moisture transport between the land and ocean and surface evapotranspiration, to investigate the decreases in land relative humidity as the climate warms. The box model is applied to simulations with idealized and full-complexity (CMIP5) general circulation models, and it is found to capture many of the features of the simulated changes in land humidity. The simplest version of the box model gives equal fractional increases in specific humidity over land and ocean. This relationship implies a decrease in land relative humidity given the greater warming over land than ocean and modest changes in ocean relative humidity, consistent with a mechanism proposed previously. When evapotranspiration is included, it is found to be of secondary importance compared to ocean moisture transport for the increase in land specific humidity, but it plays an important role for the decrease in land relative humidity. For the case of a moisture forcing over land, such as from stomatal closure, the response of land relative humidity is strongly amplified by the induced change in land surface–air temperature, and this amplification is quantified using a theory for the link between land and ocean temperatures. |
| spellingShingle | Byrne, M O'Gorman, P Understanding decreases in land relative humidity with global warming: Conceptual model and GCM simulations |
| title | Understanding decreases in land relative humidity with global warming: Conceptual model and GCM simulations |
| title_full | Understanding decreases in land relative humidity with global warming: Conceptual model and GCM simulations |
| title_fullStr | Understanding decreases in land relative humidity with global warming: Conceptual model and GCM simulations |
| title_full_unstemmed | Understanding decreases in land relative humidity with global warming: Conceptual model and GCM simulations |
| title_short | Understanding decreases in land relative humidity with global warming: Conceptual model and GCM simulations |
| title_sort | understanding decreases in land relative humidity with global warming conceptual model and gcm simulations |
| work_keys_str_mv | AT byrnem understandingdecreasesinlandrelativehumiditywithglobalwarmingconceptualmodelandgcmsimulations AT ogormanp understandingdecreasesinlandrelativehumiditywithglobalwarmingconceptualmodelandgcmsimulations |