Crop-climate feedbacks boost U.S. maize and soy yields

U.S. maize and soy production have increased rapidly since the mid-20th century. While global warming has raised temperatures in most regions over this time period, trends in extreme heat have been smaller over U.S. croplands, reducing crop-damaging high temperatures and benefiting maize and soy yields. Here we show that agricultural intensification has created a crop-climate feedback in which increased crop production cools local climate, further raising crop yields. We find that maize and soy production trends have driven cooling effects approximately as large as greenhouse gas induced warming trends in extreme heat over the central U.S. and substantially reduce them over the southern U.S., benefiting crops in all regions. This reduced warming has boosted maize and soy yields by 3.3 (2.7 – 3.9; 13.7 – 20.0%) and 0.6 (0.4 – 0.7; 7.5 – 13.7%) bu/ac/decade, respectively, between 1981 and 2019. Our results suggest that if maize and soy production growth were to stagnate, the ability of the crop-climate feedback to mask warming would fade, exposing U.S. crops to more harmful heat extremes.

Aerosols Direct Radiative Effects Combined Ground-Based Lidar and Sun-Photometer Observations: Cases Comparison between Haze and Dust Events in Beijing

Aerosols can affect vertical thermal structure during heavily polluted episodes (HPEs). Here, we selected four typical HPEs in 2018, which were further subdivided into dust and haze events. The vertical distribution of aerosols extinction coefficient (EC) and variations in columnar optical properties were investigated based on sun-photometer and Lidar observation at an urban site in Beijing. The vertical characteristics in shortwave radiative heating rate (HR) of aerosols were studied using NASA/Goddard radiative transfer model along with observational data. In the haze episode, EC layer is less than 1.5 km and shows strong scattering, with single-scattering albedo (SSA440nm) of ~0.97. The heating effects are observed at the middle and upper atmosphere, and slight heating effects are found at the lower layer. The mean HR within 1.5 km can be up to 16.3 K day−1 with EC of 1.27 km−1, whereas the HR within 0.5 km is only 1.3 K day−1. In the dust episode, dust aerosols present the absorption with SSA440nm of ~0.88, which would heat the lower atmosphere to promote vertical turbulence, and the height of EC layer can be up to 2.0–3.5 km. In addition, the strong heating effects of dust layer produced cooling effects near the surface. Therefore, the accurate measurement of aerosols optical properties in HPEs is of great significance for modeling aerosols direct radiative effects.

Changes in forest composition and associated biophysical climate feedbacks across boreal North America

Deciduous tree cover is expected to increase in North American boreal forests with climate warming and wildfire occurrence. This shift in composition can generate biophysical cooling effects via increased land surface albedo. Here we use newly derived maps of continuous tree canopy and fractional deciduous cover to assess change over recent decades. We find on average a small net decrease in deciduous fraction cover from 2000 to 2015 across boreal North America, and from 1992 to 2015 across Canada, despite extensive fire disturbance that locally increased deciduous vegetation. We further find a near-neutral net biophysical change in radiative forcing across the domain due to relatively small net changes in albedo. Thus, while there have been widespread changes in forest composition over the past several decades across the domain, the net changes in composition and associated post-fire radiative forcing have not yet induced systematic negative feedbacks to climate warming.

Do natural landscapes contribute to reducing Land Surface Temperature (LST)? A case study from Muthurajawela wetland, Sri Lanka

Microclimate regulation is one of the most significant ecosystem services provided by wetlands. The present study attempted to investigate the cooling effect provided by Muthurajawela, a coastal Ramsar wetland using Remote Sensing and GIS. The variation of Land Surface Temperatures (LST) over different land use categories of natural (water bodies, marsh, thick vegetation, grassland) and anthropogenic (built-up areas, coconut cultivations and bare lands) areas in 2015 and 2020. Parameters including Satellite Brightness Temperature, Normalized Difference Vegetation Index, Proportion of Vegetation and Land Surface Emissivity were calculated along eight transects starting from the center of the water body and extending up to 5 km from the boundary of the wetland. The results revealed that LST over areas under natural land cover (2015 - mean 25.040C, 2020 - mean 23.360C) were significantly lower than that of areas under anthropogenic influence (2015 - mean 26.520C and 2020 - mean 26.220C). The lowest increase of LST was over the water body and the highest was over the built-up areas indicating the buffering capacity of wetlands. As air temperatures are highly linked to LST, our findings suggest that wetlands contribute to lower atmospheric temperature and offer cooling effects during dry months. Acknowledging the importance of wetlands in reducing temperature, at least in a local scale, justifies the need of conserving these ecosystems, as seeking mitigatory measures for climate change driven frequent heating effects is challenging.

Air temperature variability in high-elevation glacierized regions: observations from six catchments on the Tibetan Plateau

Near-surface air temperature variability and the reliability of temperature extrapolation within glacierized regions are important issues for hydrological and glaciological studies that remain elusive because of the scarcity of high-elevation observations. Based on air temperature data in 2019 collected from 12 automatic weather stations, 43 temperature loggers and 6 national meteorological stations in six different catchments, this study presents air temperature variability in different glacierized/nonglacierized regions and assesses the robustness of different temperature extrapolations to reduce errors in melt estimation. The results show high spatial variability in temperature lapse rates (LRs) in different climatic contexts, with the steepest LRs located on the cold-dry northwestern Tibetan Plateau and the lowest LRs located on the warm-humid monsoonal-influenced southeastern Tibetan Plateau. Near-surface air temperatures in high-elevation glacierized regions of the western and central Tibetan Plateau are less influenced by katabatic winds and thus can be linearly extrapolated from off-glacier records. In contrast, the local katabatic winds prevailing on the temperate glaciers of the southeastern Tibetan Plateau exert pronounced cooling effects on the ambient air temperature, and thus, on-glacier air temperatures are significantly lower than that in elevation-equivalent nonglacierized regions. Consequently, linear temperature extrapolation from low-elevation nonglacierized stations may lead to as much as 40% overestimation of positive degree days, particularly with respect to large glaciers with a long flowline distances and significant cooling effects. These findings provide noteworthy evidence that the different LRs and relevant cooling effects on high-elevation glaciers under distinct climatic regimes should be carefully accounted for when estimating glacier melting on the Tibetan Plateau.

Experimental Investigation on Filtration and Cooling Effect of Kitchen Hood Ventilation System from Water-Mist Recirculation Spray: Water-Mist Spray Cycle

A Water-mist spray system in several heavy-duty kitchen hood canopies is installed to efficiently control the high heat loads and grease emissions produced from the cooking process and for safety purposes. The main purpose of this study is to reduce water consumption by introducing the water-mist recirculation system to replace the current method water-mist system since it is working as water loss. A standard ASTM 2519 and UL 1046 full-scaled experiment is developed in the laboratory. An existing Halton Europe/Asian water-mist operating system is adopted in this study. Twelve (12) cycles (at 24 hours of water-mist activation) have been studied to determine the maximum water-mist activation cycle. The data are collected at two (2) hours water-mist activation at every water-mist recirculation cycle. The water-mist spray fluids viscosity is 0.7 cP from fresh water until the 4th cycle (8 hours water-mist spray) and increase 14.29% (0.8 cP) at the 5th cycle to the 12th cycle. On average, the difference in gas emissions percentage for CO concentration between fresh water until the 4th cycle is 10.81 – 18.92% while the CO2 concentration is 12.33 – 18.22%. On average, the difference in cooling effects percentage for ducting temperature between fresh water until the 4th cycle is 5.55% while the hood temperature is 2.33%. From the study, the water-mist recirculation system could save up to 611,667 litres per year and 466,798.5 litres per year water for all U.S, European, and Asian kitchen hood designs per hood length. By adopting the new water-mist recirculation system to the current water-mist kitchen hood, the water operational cost for water successfully reduced to RM 4,889.63 per year and RM 6,977.86 per year for U.S design and European or Asian design per hood length respectively. The water-mist recirculation system has great potential to improve the current water-mist system for the commercial kitchen hood.

Biophysical feedback of forest canopy height on land surface temperature over contiguous United States

Forests are considered important to the mitigation of climate change. Biophysical effects of afforestation and deforestation on land surface temperature (LST) have been extensively documented. As a fundamental variable of forest structure, however, few studies have investigated the biophysical feedback of forest canopy height changes on LST at large scale. This study is designed to investigate the impact of forest canopy height changes on local land LST and clarify the biophysical processes controlling LST change from 2003 to 2005 over contiguous United States (CONUS) based on satellite observations. To this end, one satellite-based forest canopy height product is selected, and space-for-time approach together with energy balance equation is applied. Results show that for different forest types, namely evergreen forest (EF), deciduous forest (DF), and mixed forest (MF), taller forests present a net cooling effect (0.056 to 0.448 K) than shorter forests at annual scale. The increase in net radiation and sensible heat flux was less than the increase in the latent heat flux when forest canopy height classes converting from shorter to taller, resulting in annual net cooling effects. Furthermore, the cooling effect of EF is stronger than DF and MF, whether for tall, medium, or short forest canopy height classes. Multiple regression analysis reveals that the changes in biophysical components can effectively explain the LST change during growing season. Our findings provide a new insight for forest management decision in the purpose of mitigating climate warming.

Experimental investigation of desiccant dehumidification based thermoelectric air-conditioning system

Vapor compression refrigeration system (VCRS) based conventional cooling systems run on the high amount of electricity and refrigerants responsible for greenhouse emissions. To save the environment and high-grade energy, traditional cooling systems should be replaced with some environment-friendly alternative. This paper proposed alternative eco-friendly air-conditioning systems based on an amalgam of two different technologies, i.e., desiccant dehumidification and thermoelectric (TE) cooling. The proposed air-conditioning system has the following subprocess: dehumidification of moist air by the solid desiccant wheel, cooling of processed air by TE modules, and regeneration of desiccant wheel by an electric heater and waste heat from TE modules. The air conditioning system has been experimentally studied for cooling performance, cooling effect, and energy input. The maximum coefficient of performance of 0.865 can be achieved with the proposed system, and it can be used for cooling effects up to 1442.24 W to maintain the human comfort condition in the chamber i.e. approximately 22 ℃ and RH 50% defined by ASHRAE.