title: Asymmetric effects of daytime and night-time warming on Northern Hemisphere vegetation.
abstract: Temperature data over the past five decades show faster warming of the global land surface during the night than during the day. This asymmetric warming is expected to affect carbon assimilation and consumption in plants, because photosynthesis in most plants occurs during daytime and is more sensitive to the maximum daily temperature, Tmax, whereas plant respiration occurs throughout the day and is therefore influenced by both Tmax and the minimum daily temperature, Tmin. Most studies of the response of terrestrial ecosystems to climate warming, however, ignore this asymmetric forcing effect on vegetation growth and carbon dioxide (CO2) fluxes. Here we analyse the interannual covariations of the satellite-derived normalized difference vegetation index (NDVI, an indicator of vegetation greenness) with Tmax and Tmin over the Northern Hemisphere. After removing the correlation between Tmax and Tmin, we find that the partial correlation between Tmax and NDVI is positive in most wet and cool ecosystems over boreal regions, but negative in dry temperate regions. In contrast, the partial correlation between Tmin and NDVI is negative in boreal regions, and exhibits a more complex behaviour in dry temperate regions. We detect similar patterns in terrestrial net CO2 exchange maps obtained from a global atmospheric inversion model. Additional analysis of the long-term atmospheric CO2 concentration record of the station Point Barrow in Alaska suggests that the peak-to-peak amplitude of CO2 increased by 23 ± 11% for a +1 °C anomaly in Tmax from May to September over lands north of 51° N, but decreased by 28 ± 14% for a +1 °C anomaly in Tmin. These lines of evidence suggest that asymmetric diurnal warming, a process that is currently not taken into account in many global carbon cycle models, leads to a divergent response of Northern Hemisphere vegetation growth and carbon sequestration to rising temperatures.
authors.affiliation: Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.
authors.forename: Shushi
authors.initials: S
authors.lastname: Peng
authors.forename: Shilong
authors.initials: S
authors.lastname: Piao
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciais
authors.forename: Ranga B
authors.initials: RB
authors.lastname: Myneni
authors.forename: Anping
authors.initials: A
authors.lastname: Chen
authors.forename: Frédéric
authors.initials: F
authors.lastname: Chevallier
authors.forename: Albertus J
authors.initials: AJ
authors.lastname: Dolman
authors.forename: Ivan A
authors.initials: IA
authors.lastname: Janssens
authors.forename: Josep
authors.initials: J
authors.lastname: Peñuelas
authors.forename: Gengxin
authors.initials: G
authors.lastname: Zhang
authors.forename: Sara
authors.initials: S
authors.lastname: Vicca
authors.forename: Shiqiang
authors.initials: S
authors.lastname: Wan
authors.forename: Shiping
authors.initials: S
authors.lastname: Wang
authors.forename: Hui
authors.initials: H
authors.lastname: Zeng
mesh_terms: D002244:Carbon / Q000378:metabolism; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration; D002940:Circadian Rhythm; D003624:Darkness; D017753:Ecosystem; D005843:Geography; D057232:Global Warming; D010788:Photosynthesis / Q000528:radiation effects; D010944:Plants / Q000378:metabolism* / Q000528:radiation effects; D013472:Sunlight; D013696:Temperature
chemical_list: D002245:Carbon Dioxide; D002244:Carbon