Multiple lines of evidence 1,2 have established the existence of a land carbon sink in the northern hemisphere, but its trend remains poorly understood 3,4 . Here we show from measurements of the atmospheric CO2 gradient between the stations of Mauna Loa (north) and of South Pole (south) since 1958 that the northern land sink remained rather stable between the 1960s and the late 1980s, but increased by 0.5 ± 0.4 Pg C yr -1 during the 1990s and further by 0.6 ± 0.5 Pg C yr -1 during the 2000s. The first increase of the northern land sink in the 1990s accounts for 65% of the increase in the global land flux during that period. The subsequent increase in the 2000s is larger than the increase of the global land flux, suggesting a coincident decrease of carbon uptake in southern regions. The decadal change in the northern land sink between the 1960s and the 1990s can be explained with a combination of rising atmospheric CO2, climate variability, and changes in land-cover as represented in an ensemble of terrestrial carbon cycle models 4 . The increase during the 2000s is however underestimated by all terrestrial models. Reducing uncertainties involve better consideration of changes in drivers such as land use change, diffuse light, and nitrogen deposition as well as denser observations to clarify the importance of different regions.Fossil fuel and land-use change emissions of CO2 into the atmosphere increased by a factor of three between 1960 and 2016, with a fast growth rate in the 1980s, a slower growth rate in the 1990s and a re-acceleration 5 in the 2000s. The global land and ocean carbon sinks increased proportionally with growing emissions 6 but their location and trends are incompletely understood. Northern Hemisphere (NH) lands make a dominant contribution to the global land carbon sink 1-4,7-8 . In the NH mid and high latitudes, vegetation greenness increased in the last 30 years 9 , and the seasonal amplitude of CO2 increased by 50% in the last 50 years 10 , suggesting an enhancement of ecosystem production.However, these observations are not proofs that the NH net carbon sink is increasing because of possible upward trends in soil respiration 11 and land-use emissions compensating for increased production.To gain insights on the long-term trend in the northern land sink over the last 50 years, we use the inter-hemispheric gradient of atmospheric CO2 (IG) defined as the observed difference of atmospheric CO2 between the Mauna-Loa (MLO) station located at 19°N, and South Pole (SPO).Both MLO and SPO record CO2 growth rates representative of the means in their respective hemisphere 12 . Here we examine the relationship between IG and fossil fuel and cement CO2 emissions (F) between 1958 and 2016, and recent changes during the 2000s, a period marked by the acceleration of global CO2 emissions, mainly from East and South Asia regions [13][14] .From 1958 to 2016 the IG grew proportional to F (Fig. 1; Fig. ED1) with a Pearson correlation coefficient (r) of 0.97 (p <0.01) and a mean regression slope 15 of 0.44± 0.01...

Ceramic aerogels are attractive candidates for high-temperature thermal insulation, catalysis support, and ultrafiltration materials, but their practical applications are usually limited by brittleness. Recently, reversible compressibility has been realized in flexible nanostructures-based ceramic aerogels. However, these modified aerogels still show fast and brittle fracture under tension. Herein, we demonstrate achieving reversible stretch and crack insensitivity in a highly compressible ceramic aerogel through engineering its microstructure by using curly SiC-SiO x bicrystal nanowire as the building blocks. The aerogel exhibits large-strain reversible stretch (20%) and good resistance to high-speed tensile fatigue test. Even for a prenotched sample, a reversible stretch at 10% strain is achieved, indicating good crack resistance. The aerogel also displays reversible compressibility up to 80% strain, ultralow thermal conductivity of 28.4 mW m–1 K–1, and excellent thermal stability even at temperatures as high as 1200 °C in butane blow torch or as low as −196 °C in liquid nitrogen. Our findings show that the attractive tensile properties arise from the deformation, interaction, and reorientation of the curly nanowires which could reduce stress concentration and suppress crack initiation and growth during tension. This study not only expands the applicability of ceramic aerogels to conditions involving complex dynamic stress under extreme temperature conditions but also benefits the design of other highly stretchable and crack-resistant porous ceramic materials for various applications.

A simple, cheap and rapid method is developed to fabricate glass microfluidic devices with dry film photoresist as pattern transfer masks for wet etching, which provides an efficient approach for mass-production of glass microchips.

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Lightweight materials such as porous ceramics have attracted increasing attention for applications in energy conservation, aerospace and automobile industries. However, porous ceramics are usually weak and brittle; in particular, tiny defects could cause catastrophic failure, which affects their reliability and limits the potential use greatly. Here we report a SiC/SiO 2 nanowire network constructed from numerous well-bonded SiC nanowires coated by a biphasic structure consisting of amorphous SiO 2 and nanocrystal SiC. The as-obtained SiC/ SiO 2 nanowire network is lightweight (360 ± 10 mg cm −3 ), mechanically strong (compressive strength of 16 MPa), and damage-tolerant. The high strength of the network is attributed to the biphasic mixed structure of the binding coating which can restrict the deformation of nanowires upon compression. The lightweight and strong SiC/SiO 2 nanowire network shows potential for engineering applications in harsh environments.

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