Net Warming Research Articles

Climate change mitigation potential of wetlands and the cost-effectiveness of their restoration.

The cost-effective mitigation of climate change through nature-based carbon dioxide removal strategies has gained substantial policy attention. Inland and coastal wetlands (specifically boreal, temperate and tropical peatlands; tundra; floodplains; freshwater marshes; saltmarshes; and mangroves) are among the most efficient natural long-term carbon sinks. Yet, they also release methane (CH4) that can offset the carbon they sequester. Here, we conducted a meta-analysis on wetland carbon dynamics to (i) determine their impact on climate using different metrics and time horizons, (ii) investigate the cost-effectiveness of wetland restoration for climate change mitigation, and (iii) discuss their suitability for inclusion in climate policy as negative emission technologies. Depending on metrics, a wetland can simultaneously be a net carbon sink (i.e. boreal and temperate peatlands net ecosystem carbon budget = -28.1 ± 19.13 gC m-2 y-1) but have a net warming effect on climate at the 100 years time-scale (i.e. boreal and temperate peatland sustained global warming potential = 298.2 ± 100.6 gCO2 eq-1 m-2 y-1). This situation creates ambivalence regarding the effect of wetlands on global temperature. Moreover, our review reveals high heterogeneity among the (limited number of) studies that document wetland carbon budgets. We demonstrate that most coastal and inland wetlands have a net cooling effect as of today. This is explained by the limited CH4 emissions that undisturbed coastal wetlands produce, and the long-term carbon sequestration performed by older inland wetlands as opposed to the short lifetime of CH4 in the atmosphere. Analysis of wetland restoration costs relative to the amount of carbon they can sequester revealed that restoration is more cost-effective in coastal wetlands such as mangroves (US$1800 ton C-1) compared with inland wetlands (US$4200-49 200 ton C-1). We advise that for inland wetlands, priority should be given to conservation rather than restoration; while for coastal wetlands, both conservation and restoration may be effective techniques for climate change mitigation.

Dust radiative forcing and its impact on surface energy budget over West Africa

Dust is the dominant aerosol type over West Africa (WA), and therefore accurate simulation of dust impact is critical for better prediction of weather and climate change. The dust radiative forcing (DRF) is estimated using two sets of experiments in this study: one without and the other with dust aerosol and its feedbacks with the Weather Research and Forecasting with Chemistry model (WRF-Chem). Results show that DRF presents a net warming effect at the top-of-atmosphere (TOA) and in the atmosphere (ATM), and cooling at the surface (SFC). The net DRF over WA is estimated to be 9 W/m2 at the TOA, 23 W/m2 in the ATM, and − 13 W/m2 at the SFC. Furthermore, dust-induced a reduction of sensible heat up to 24 W/m2 and SFC temperature up to 2 °C cooling over WA, an increase of latent heat up to 12 W/m2 over Sahara, a decrease up to 24 W/m2 over the vegetated surfaces and an increase in the surface energy balance up to 12 W/m2 over WA. The presence of dust significantly influences the surface energy budget over WA, suggesting that dust effects should be considered in more climate studies to improve the accuracy of climate predictions.

Surface Warming During the 2018/Mars Year 34 Global Dust Storm.

The impact of Mars's 2018 Global Dust Storm (GDS) on surface and near‐surface air temperatures was investigated using an assimilation of Mars Climate Sounder observations. Rather than simply resulting in cooling everywhere from solar absorption (average surface radiative flux fell 26 W/m2), the globally averaged result was a 0.9‐K surface warming. These diurnally averaged surface temperature changes had a novel, highly nonuniform spatial structure, with up to 16‐K cooling/19‐K warming. Net warming occurred in low thermal inertia regions, where rapid nighttime radiative cooling was compensated by increased longwave emission and scattering. This caused strong nightside warming, outweighing dayside cooling. The reduced surface‐air temperature gradient closely coupled surface and air temperatures, even causing local dayside air warming. Results show good agreement with Mars Climate Sounder surface temperature retrievals. Comparisons with the 2001 GDS and free‐running simulations show that GDS spatial structure is crucial in determining global surface temperature effects.

Global warming impacts of nitrogen use in agriculture: an assessment for India since 1960

ABSTRACT Global warming impacts of N use in Indian agriculture since 1960 was estimated for 20- and 100-year time scales using equation-based empirical method. During 2014, total Warming in terms of global temperature change potential (GTP) for a 20-year time scale (GTP20) was assessed as 217.31 ± 17.74 Tg CO2e, and for a 100-year time scale (GTP100) was 217.78 ± 17.78 Tg CO2e. N2O contributed 90% and 99%of the GTP20 and GTP100, respectively. Total cooling impacts were 94.86 ± 7.75 and 50.36 ± 4.11 Tg CO2e on GTP20 and GTP100, respectively. Aerosols of NH3 and NOx, NOx-induced O3 and CH4 alteration, and N-induced C sequestration contributed 41, 6 and 51%, respectively, to GTP20, however, N-induced C sequestration contributed about 99% to GTP100. Net warming impacts were 122.45 ± 10.00 and 167.42 ± 13.67 Tg CO2e on GTP20 and GTP100, respectively. Net warming impacts were lowered by 10% and 1% compared to total warming, and 37% and 23% compared to warming caused by N2O alone, for GTP20 and GTP100, respectively. Usually, to estimate the global warming impacts of N use in agriculture, the warming effects of only N2O emission are considered. However, both warming and cooling impacts should be considered to capture the net impacts of N use in agriculture on climate change.

Enhanced Dust Influx to South Atlantic Sector of Antarctica During the Late‐20th Century: Causes and Contribution to Radiative Forcing

AbstractAtmospheric dust influences global climate and ocean biogeochemistry. Here we present a high‐resolution ice core dust record (1905–2005 CE) from coastal Dronning Maud Land (71°20′S, 11°35′E), East Antarctica, to understand dust flux variability, its causes, and potential contribution to radiative forcing during the 20th century in the South Atlantic sector of East Antarctica (SASA). The dust flux profile (sum of 1–25 μm size fractions) reveals three stepwise increase during 1905–1929, 1930–1979, and 1980–2005 CE time with an average of 0.83, 4.7, and 12.88 mg·m−2·year−1, respectively. Our investigation for such dramatic dust flux increase reveals that the increased aridity and favorable wind conditions over Southern South America (SSA), a potential dust source to Antarctica, caused increase in dust production and transport during the late 20th century. The dust flux variability in Southern Hemisphere is concomitant with in‐phase relationship between El‐Niño Southern Oscillation and Pacific Decadal Oscillations, which influenced the spatial distribution of global wet‐dry phase (precipitation pattern). Further, shifting of Southern Annular Mode to positive phase made wind conditions more conducive for long‐range dust transport from SSA to coastal Dronning Maud Land region. To the best of our knowledge, this is the first report of past radiative forcing estimates for Antarctica using ice core dust record into a radiative transfer model. Our estimates of radiative forcing corresponding to the enhanced dust flux yield nearly 30% increase in aerosol forcing during the late 20th century. This has resulted 40% decrease in atmospheric cooling rate, which contributed to net atmospheric warming over SASA.

Reforestation and surface cooling in temperate zones: Mechanisms and implications.

Land-use/cover change (LUCC) is an important driver of environmental change, occurring at the same time as, and often interacting with, global climate change. Reforestation and deforestation have been critical aspects of LUCC over the past two centuries and are widely studied for their potential to perturb the global carbon cycle. More recently, there has been keen interest in understanding the extent to which reforestation affects terrestrial energy cycling and thus surface temperature directly by altering surface physical properties (e.g., albedo and emissivity) and land-atmosphere energy exchange. The impacts of reforestation on land surface temperature and their mechanisms are relatively well understood in tropical and boreal climates, but the effects of reforestation on warming and/or cooling in temperate zones are less certain. This study is designed to elucidate the biophysical mechanisms that link land cover and surface temperature in temperate ecosystems. To achieve this goal, we used data from six paired eddy-covariance towers over co-located forests and grasslands in the temperate eastern United States, where radiation components, latent and sensible heat fluxes, and meteorological conditions were measured. The results show that, at the annual time scale, the surface of the forests is 1-2°C cooler than grasslands, indicating a substantial cooling effect of reforestation. The enhanced latent and sensible heat fluxes of forests have an average cooling effect of -2.5°C, which offsets the net warming effect (+1.5°C) of albedo warming (+2.3°C) and emissivity cooling effect (-0.8°C) associated with surface properties. Additional daytime cooling over forests is driven by local feedbacks to incoming radiation. We further show that the forest cooling effect is most pronounced when land surface temperature is higher, often exceeding -5°C. Our results contribute important observational evidence that reforestation in the temperate zone offers opportunities for local climate mitigation and adaptation.

Effect of terrestrial vegetation growth on climate change in China

Globally, some vegetation has grown significantly over the past decades, but the climate benefits remain unclear, especially in the temperate regions. Understanding the biophysical effects and identifying the potential of vegetation will help to mitigate climate change. Here, we propose a vegetation-adjusted temperature index to understand how terrestrial vegetation growth in China affects the air temperature for 2001–2013, based on satellite-derived normalized difference vegetation index, near-surface air temperature (Ta) and the land surface temperature. Grassland growth and cropland growth are found to cool the Ta by −0.08 ± 0.32 °C (mean ± one standard deviation) and −0.06 ± 0.28 °C, respectively. Forest growth results in net climate warming by 0.05 ± 0.29 °C. Biophysical effects, elevation and background climate are used to explain the climate impacts of vegetation. Results show that the biophysical effects dominate the climate impact. More specifically, evapotranspiration (ET) controls the daytime climate impact, and at night, an indirect effect of albedo (the release of daytime heat storage) dominates it. Lower precipitation, temperature and elevation reinforce the warming potential. Moreover, the effects of albedo and ET on climate are nonlinear. During the day, although lower albedo absorbs more incoming radiation, it releases more extra heat per unit ET that can compensate for the increased incoming radiation. At night, the warming effect reflects the release of daytime heat storage. Overall, tropical vegetation growth (−0.04 ± 0.10 °C) and warm temperate vegetation growth (−0.08 ± 0.15 °C) achieve the climatic benefits. Overall, the method proposed contributes to quantitatively evaluate the role of afforestation plan on regional climate cooling, and provides some policy/practical implications for future afforestation projects. Future afforestation projects should carefully consider the biophysical process and background climate to mitigate climate change.

The Summer Heat Balance of the Oregon Inner Shelf Over Two Decades: Mean and Interannual Variability

AbstractSummer temperature and velocity measurements from 14 years in 15 m of water over the inner shelf off Oregon were used to investigate interannual temperature variability and the capacity of the across‐shelf heat flux to buffer net surface warming. There was no observable trend in summer mean temperatures, and the standard deviation of interannual variability (0.5°C) was less than the standard deviation in daily temperatures each summer (1.6°C, on average). Yet net surface heat flux provided a nearly constant source of heat each year, with a standard deviation less than 15 of the interannual mean. The summer mean across‐shelf upwelling circulation advected warmer water offshore near the surface, cooling the inner shelf and buffering the surface warming. In most years (11 out of 14), this two‐dimensional heat budget roughly closed with a residual less than 20 of the leading term. Even in years when the heat budget did not balance, the observed temperature change was negligible, indicating that an additional source of cooling was needed to close the budget. A comparison of the residual to the interannual variability in fields such as along‐shelf wind stress, stratification, and along‐shelf currents found no significant correlation, and further investigation into the intraseasonal dynamics is recommended to explain the results. An improved understanding of the processes that contribute to warming or cooling of the coastal ocean has the potential to improve predictions of the impact of year‐to‐year changes in local winds and circulation, such as from marine heat waves or climate change, on coastal temperatures.

The regional temperature implications of strong air quality measures

Abstract. Anthropogenic emissions of short-lived climate forcers (SLCFs) affect both air quality and climate. How much regional temperatures are affected by ambitious SLCF emission mitigation policies is, however, still uncertain. We investigate the potential temperature implications of stringent air quality policies by applying matrices of regional temperature responses to new pathways for future anthropogenic emissions of aerosols, methane (CH4), and other short-lived gases. These measures have only a minor impact on CO2 emissions. Two main options are explored, one with climate optimal reductions (i.e., constructed to yield a maximum global cooling) and one with the maximum technically feasible reductions. The temperature response is calculated for four latitude response bands (90–28∘ S, 28∘ S–28∘ N, 28–60∘ N, and 60–90∘ N) by using existing absolute regional temperature change potential (ARTP) values for four emission regions: Europe, East Asia, shipping, and the rest of the world. By 2050, we find that global surface temperature can be reduced by -0.3±0.08 ∘C with climate-optimal mitigation of SLCFs relative to a baseline scenario and as much as −0.7 ∘C in the Arctic. Cutting CH4 and black carbon (BC) emissions contributes the most. The net global cooling could offset warming equal to approximately 15 years of current global CO2 emissions. On the other hand, mitigation of other SLCFs (e.g., SO2) leads to warming. If SLCFs are mitigated heavily, we find a net warming of about 0.1 ∘C, but when uncertainties are included a slight cooling is also possible. In the climate optimal scenario, the largest contributions to cooling come from the energy, domestic, waste, and transportation sectors. In the maximum technically feasible mitigation scenario, emission changes from the industry, energy, and shipping sectors will cause warming. Some measures, such as those in the agriculture waste burning, domestic, transport, and industry sectors, have large impacts on the Arctic, especially by cutting BC emissions in winter in areas near the Arctic.

Seasonal Changes in the North Atlantic Cold Anomaly: The Influence of Cold Surface Waters From Coastal Greenland and Warming Trends Associated With Variations in Subarctic Sea Ice Cover

AbstractWorldwide sea surface temperatures (SST) have increased on average by about 1 °C since 1900 with the exception of a region of the North Atlantic subpolar gyre near 50°N which has cooled by up to 0.9 °C over the same period, generating the negative feature on temperature anomaly maps which has been colloquially described by Rahmstorf et al. (2015, https://doi.org/10.1038/nclimate2554) as the “cold blob” (abbreviated here CB). This unique long‐term surface cooling trend is most evident in February, but in August net warming is observed even at CB epicenter and the CB itself is reduced to a mere “warming hole.” These seasonal changes in the intensity of the CB are the product of two separate factors: (1) a long‐term winter cooling specific for the CB region which appears to be associated with cooling of Greenland coastal waters in autumn, plausibly linked to summer meltwater from icebergs and sea ice and (2) summer warming effects which derive from (a) dramatic reduction in summer sea ice cover in the sub‐Arctic over the last 30 years that allows enhanced absorption of sunlight by the new open water in summer and (b) an unusual period of increased summer sub‐Arctic ice cover in the early twentieth century, which lowers the SST baseline measured from 1900, thus increasing the calculated linear rate of change of SST with time. Both of these effects could contribute to the observed Arctic amplification of warming.

Beaver dam influences on streamflow hydraulic properties and thermal regimes

Beaver dams alter channel hydraulics which in turn change the geomorphic templates of streams. Variability in geomorphic units, the building blocks of stream systems, and water temperature, critical to stream ecological function, define habitat heterogeneity and availability. While prior research has shown the impact of beaver dams on stream hydraulics, geomorphic template, or temperature, the connections or feedbacks between these habitat measures are not well understood. This has left questions regarding relationships between temperature variability at different spatial scales to hydraulic properties such as flow depth and velocity that are dependent on the geomorphology. We combine detailed predicted hydraulic properties, field-based maps with an additional classification scheme of geomorphic units, and detailed water temperature observations throughout a study reach to demonstrate the relationship between these factors at different spatial scales (reach, beaver dam complexes, and geomorphic units). Over a three-week, low flow period we found temperature to vary 2 °C between the upstream and downstream extents of the reach with a net warming of 1 °C during the day and a net cooling of 0.5 °C at night. At the beaver dam complex scale, net warming of 1.15 °C occurred during the day with variable cooling at night. Regardless of limited temperature changes at these larger scales, the temperature variability within a beaver dam complex reached up to 10.5 °C due to the diversity of geomorphic units. At the geomorphic unit scale, the highly altered flow velocity and depth distributions within primary geomorphic units provide an explanation of the temperature variability within the dam complex and insight regarding increases in habitat heterogeneity.

How Does Cloud Overlap Affect the Radiative Heating in the Tropical Upper Troposphere/Lower Stratosphere?

AbstractCharacterizing two‐layer cloud systems has historically been difficult. These systems have a strong radiative impact on the composition of and the processes in the upper troposphere‐lower stratosphere (UTLS). Using 4 years of combined spaceborne lidar and radar observations, the radiative impact of two‐layer cloud systems in the tropical UTLS is characterized, and its sensitivity to the properties of top‐ and bottom‐layer clouds is further quantified. Under these overlapping cloud conditions, the bottom‐layer clouds can fully suppress the radiative heating caused by high clouds in the UTLS, by inducing strong longwave cooling. If the vertical separation between the layers is <4 km, the radiative heating of the high cloud changes sign from positive to negative. Furthermore, the radiative effect at the top of the atmosphere is investigated, and it is found that the characteristic net warming by cirrus with ice water path <50 g/m2 is suppressed in the two‐layered system.

Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model

Abstract. The northward flow of the upper limb of the Atlantic Meridional Overturning Circulation (AMOC) is fed by waters entering the South Atlantic from the Indian Ocean mainly via the Agulhas Current (AC) system and by waters entering from the Pacific through Drake Passage (DP), commonly referred to as the “warm” and “cold” water routes, respectively. However, there is no final consensus on the relative importance of these two routes for the upper limb's volume transport and thermohaline properties. In this study we revisited the AC and DP contributions by performing Lagrangian analyses between the two source regions and the North Brazil Current (NBC) at 6∘ S in a realistically forced high-resolution (1∕20∘) ocean model. Our results agree with the prevailing conception that the AC contribution is the major source for the upper limb transport of the AMOC in the tropical South Atlantic. However, they also suggest a non-negligible DP contribution of around 40 %, which is substantially higher than estimates from previous Lagrangian studies with coarser-resolution models but now better matches estimates from Lagrangian observations. Moreover, idealized analyses of decadal changes in the DP and AC contributions indicate that the ongoing increase in Agulhas leakage indeed may have induced an increase in the AC contribution to the upper limb of the AMOC in the tropics, while the DP contribution decreased. In terms of thermohaline properties, our study highlights the fact that the AC and DP contributions cannot be unambiguously distinguished by their temperature, as the commonly adopted terminology may imply, but rather by their salinity when entering the South Atlantic. During their transit towards the NBC the bulk of DP waters experiences a net density loss through a net warming, whereas the bulk of AC waters experiences a slight net density gain through a net increase in salinity. Notably, these density changes are nearly completely captured by Lagrangian particle trajectories that reach the surface mixed layer at least once during their transit, which amount to 66 % and 49 % for DP and AC waters, respectively. This implies that more than half of the water masses supplying the upper limb of the AMOC are actually formed within the South Atlantic and do not get their characteristic properties in the Pacific and Indian Oceans.

Impacts of climate warming, cultivar shifts, and phenological dates on rice growth period length in China after correction for seasonal shift effects

Crop phenology changes are important indicators of climate change. Climate change impacts on crop phenology are generally investigated through statistical analysis of the relationship between growth period length and growth period mean temperature. However, growth periods may be either earlier or later in a given year; hence, changes in mean temperature indicate both the effects of climate change and those attributable to seasonal temperature differences. Failure to consider temperature change resulting from seasonal shifts can lead to biased estimation of warming trends and their corresponding impact on phenology. We evaluated this potential bias in rice phenology change in 892 phenology series from China by applying time series regression control for phenological dates. The results indicate that the true magnitudes of climate change for early rice, late rice, and single rice are 0.20–0.56, 0.23–0.86, and 0.28–0.38 K/decade, after correction for the effects of seasonal shifts. The effects of seasonal shifts of growth periods led to underestimates of the magnitude of climate change by 0.16–0.22 and 0.05–0.08 K/decade for early rice and single rice, respectively, and an overestimate of the effect for late rice of 0.02–0.06 K/decade. Correspondingly, the net warming impacts on growth period length after correcting for the effects of seasonal shifts were − 2.7 d/K for early rice, − 4.8 d/K for late rice, and − 3.1 d/K for single rice, which were weaker for early and single rice, but stronger for late rice, relative to previous reports. Changes in growth period length were most closely associated with variation in phenological dates, while their relationship with climate change was less pronounced. Our results indicate that earlier phenological dates and prolonged-duration cultivars have been adopted to offset the impact of climate change, providing further evidence of active adaptation of rice cultivation practice to climate change in China.

Reduced Nearshore Warming Associated With Eastern Boundary Upwelling Systems

Coastal marine biodiversity within eastern boundary upwelling systems (EBUS) is closely linked to the cooler sea temperatures associated with them. It has been suggested that global warming could lead to enhanced sea surface cooling in EBUS via the intensification of upwelling-favorable winds. Conversely, increased stratification and the widespread warming of the world's oceans could drive these systems in the opposite direction. These competing mechanisms hold the potential for driving the thermal envelopes of EBUS towards – or away from – the thermal envelopes found outside EBUS, with likely contrasting implications for biodiversity conservation in each scenario. Here we characterize the patterns of net sea surface warming rates over more than three decades throughout the global ocean to evaluate if waters inside EBUS are changing differently from those outside EBUS. Results point to a trend of reduced warming inside EBUS, especially along the nearshore. We found that reduced net warming was prevalent in Pacific EBUS but restricted in Atlantic EBUS. In contrast, net warming in the coastal ocean outside EBUS was pervasive and generally associated with proximity to land. Our results suggest that EBUS have been responding to climate change differently from the rest of the global ocean, potentially buffering coastal biomes from decades of global warming.

Net Global Warming Potential of Spring Wheat Cropping Systems in a Semiarid Region

Investigations of global warming potential (GWP) of semiarid cropping systems are needed to ascertain agriculture’s contributions to climate regulation services. This study sought to determine net GWP for three semiarid cropping systems under no-tillage management in the northern Great Plains of North America: spring wheat (Triticum aestivum L.)—fallow (SW-F), continuous spring wheat (CSW) and spring wheat—safflower (Carthamus tinctorius L.)—rye (Secale cereale L.) (SW-S-R). Management records, coupled with published carbon dioxide (CO2) emission estimates, were used to determine emissions from production inputs and field operations. Static chamber methodology was used to measure soil-atmosphere methane (CH4) and nitrous oxide (N2O) fluxes over a 3-year period and changes in profile soil organic carbon (SOC) stocks were determined over 18 years. Carbon dioxide emissions associated with production inputs and field operations were greatest for CSW, intermediate for SW-S-R and lowest for SW-F. All cropping systems were minor CH4 sinks (≤0.5 kg CH4-C ha−1 yr−1) and moderate N2O sources (1.0 to 2.8 kg N2O-N ha−1 yr−1). No differences in SOC stocks were observed among cropping systems (P = 0.78), nor did SOC stocks change significantly from baseline conditions (P = 0.82). Summing across factors, net GWP was positive for SW-F and CSW, implying net greenhouse gas (GHG) emission to the atmosphere, while net GWP for SW-S-R was negative, implying net GHG uptake. Net GWP, however, did not differ among cropping systems (P = 0.17). Management practices that concurrently improve N use efficiency and increase SOC stocks are needed for semiarid cropping systems to be net GHG sinks.

Implementation of Aerosol-Cloud Interaction within WRF-CHIMERE Online Coupled Model: Evaluation and Investigation of the Indirect Radiative Effect from Anthropogenic Emission Reduction on the Benelux Union

The indirect effects of aerosol are particularly important over regions where meteorological conditions and aerosol content are favourable to cloud formation. This was observed during the Intensive Cloud Aerosol Measurement Campaign (IMPACT) (European Integrated project on Aerosol Cloud Climate and Air quality Interaction (EUCAARI) project) in the Benelux Union during May 2008. To better understand this cloud formation variability, the indirect effects of aerosol have been included within the WRF-CHIMERE online model. By comparing model results to the aircraft measurements of IMPACT, to surface measurements from EMEP and AIRBASE and to MODIS satellite measurements, we showed that the model is able to simulate the variability and order of magnitude of the observed number of condensation nuclei (CN), even if some differences are identified for specific aerosol size and location. To quantify the impact of the local anthropogenic emissions on cloud formation, a sensitivity study is performed by halving the surface emissions fluxes. It is shown that the indirect radiative effect (IRE) at the surface is positive for both shortwave and longwave with a net warming of +0.99 W/m2. In addition, important instantaneous changes are modelled at local scale with up to ±6 °C for temperatures and ±50 mm/day for precipitation.

Simulated Global Climate Response to Tropospheric Ozone‐Induced Changes in Plant Transpiration

AbstractTropospheric ozone (O3) pollution is known to damage vegetation, reducing photosynthesis and stomatal conductance, resulting in modified plant transpiration to the atmosphere. We use an Earth system model to show that global transpiration response to near‐present‐day surface tropospheric ozone results in large‐scale global perturbations to net outgoing long‐wave and incoming shortwave radiation. Our results suggest that the radiative effect is dominated by a reduction in shortwave cloud forcing in polluted regions, in response to ozone‐induced reduction in land‐atmosphere moisture flux and atmospheric humidity. We simulate a statistically significant response of annual surface air temperature of up to ~ +1.5 K due to this ozone effect in vegetated regions subjected to ozone pollution. This mechanism is expected to further increase the net warming resulting from historic and future increases in tropospheric ozone.

Clarifying the role of radiative mechanisms in the spatio-temporal changes of land surface temperature across the Horn of Africa

Vegetation plays an important role in the climate system. The extent to which vegetation impacts climate through its structure and function varies across space and time, and it is also affected by land cover changes. In areas with both multiple growing periods and significant land cover changes, such as the Horn of Africa, identifying vegetation influence on land surface temperature (LST) through radiative changes needs further investigation. In this study, we used a 13-year time series (2001−2013) of remotely sensed environmental data to estimate the contribution of radiative mechanism to LST change due to growing season albedo dynamics and land cover conversion. Our results revealed that in taller woody vegetation (forest and savanna), albedo increases during the growing period by up to 0.04 compared with the non-growing period, while it decreases in shorter vegetation (grassland and shrubland) by up to 0.03. The warming impact due to a decrease in albedo during the growing period in shorter vegetation is counteracted by a considerable increase in evapotranspiration, leading to net cooling. Analysis of land cover change impact on albedo showed a regional annual average instantaneous surface radiative forcing of −0.03 ± 0.02 W m−2. The land cover transitions from forest to cropland, and savanna to grassland, displayed the largest mean albedo increase across all seasons, causing an average instantaneous surface radiative forcing of −2.6 W m−2 and − 1.5 W m−2 and a decrease in mean LST of 0.12 K and 0.09 K, all in dry period (December, January, February), respectively. Despite the albedo cooling effect in these conversions, an average net warming of 1.3 K and 0.23 K was observed under the dominant influence of non-radiative mechanisms. These results show that the impact of radiative mechanism was small, highlighting the importance of non-radiative processes in understanding the climatic impacts of land cover changes, as well as in delineating effective mitigation strategies.

Improving nitrogen and water use efficiency in a wheat-maize rotation system in the North China Plain using optimized farming practices

Excessive nitrogen (N) application and shortage of water are the major obstacles to sustainable agricultural development in the high-yielding regions of the North China Plain. New cropping systems need to be created that use integrated management practices to improve the utilization of nitrogen and water and to reduce the emissions of greenhouse gases. We conducted a 4-year (2011–2015) field experiment in Huantai county using three cropping treatments: local farmers’ conventional practices (FP), recommended farming management (REC), and no N fertilization (CK). The study revealed that, the mean annual grain yield of FP and REC was both 16.5 Mg ha−1 which was higher than CK (7.9 Mg ha−1). In comparison with FP, the REC treatment showed N fertilizer and groundwater input reduced by 43% and 28% with increasing of 79.3% and 61.7% of N use efficiency (NUE) and irrigation water use efficiency (IWUE), respectively. The REC treatment demonstrated consistently lower N2O emissions (36% on average) compared with the FP treatment. The annual net global warming potentials of the REC and CK treatments were 37% and 73% lower, respectively, than that of the FP treatment. The water footprint of the REC treatment was 30% (the Water Footprint Assessment method) to 37% (the Life Cycle Assessment method) less than that of the FP treatment. These results indicate that REC is a promising and feasible treatment for ensuring environmentally friendly, and energy-efficient sustainable agriculture in the high-yielding regions of the North China Plain.