Abstract Tipping points in the Earth system have the potential to cause major detrimental impacts to the biosphere and societies. Their inherent nonlinearity implies that even relatively small additional increases in external forcing might result in disproportionately large adjustments to components of the Earth system. In some cases, tipping points may lead to alternative states that would be difficult to return from. Here, we discuss ways to maximize the usefulness of Earth Observation (EO) data to improve Early Warning Systems of tipping points in the terrestrial biosphere. We focus on the terrestrial biosphere because it provides critical ecosystem services, offers more tractable dynamics for early warning development, and is exceptionally amenable to remote sensing across multiple spatial scales. We synthesize two key elements: potential tipping elements and dynamics in the terrestrial biosphere, and corresponding mathematical theory and methods that can determine resilience levels. With such combined knowledge, we discuss the feasibility of generating warnings of approaching tipping points, filtered through consideration of what can be remotely sensed. EO data is generally of short length in time but has extensive spatial coverage at fine resolution, leading to emphasis on spatial‐temporal resilience sensing and building early warning indicators that may incorporate parallel data on system forcing. We describe how “space‐for‐time” substitutions may capitalize on EO's strong areal coverage to understand whether ecosystems might be nearer to tipping depending on location, enabling more complete assessment of emerging signals on the approach to strong nonlinearities.
Abstract This article focuses on the Congo basin and western equatorial Africa (WEA). Topics include atmospheric circulation, convective systems, the character of rainfall, cloud cover, moisture and evapotranspiration, and interannual variability. Some misunderstanding exists about the seasonal cycle. It has generally been described as bimodal, with rainy seasons in the boreal spring and autumn as the Intertropical Convergence Zone (ITCZ) transits the region. This is true of only some central portions and some of the region has a unimodal seasonal cycle. More importantly, the ITCZ does not exist in this region. Intraseasonal variability is related to equatorial waves, the most important being convectively‐coupled Kelvin waves and the Madden‐Julian Oscillation. Main circulation features are the Tropical Easterly Jet, two mid‐tropospheric African Easterly Jets, and low‐level westerlies. A Walker cell exists over the region in some seasons. There is also evidence of a shallower, Walker‐type cell in the Congo basin itself. The Congo basin is the site of the world's strongest convective activity, including the world's highest lightning frequency. Dominant are Mesoscale Convective Systems, which bring convective rainfall in the afternoon and stratiform rainfall at night. As for rainfall, there is little correlation on monthly or annual time scales between rainfall at various stations. The factors in interannual variability in the Congo basin are not well understood. In WEA sea‐surface temperatures are important. El Niño‐Southern Oscillation appears to have little influence, but the Indian Ocean dipole has some influence in the east. Other factors include changes in the Walker circulation, the African thermal lows, and the low‐level westerlies.
Abstract Fire plumes are rising columns of heated air masses, consisting of gaseous and particulate matter generated by combustion, affecting air quality, climate and public health. The chemical species released undergo secondary reactions and participate in chemical and physical interactions, altering the properties of the fire plume. The ability of the plume to be transported across short and long distances, depending on the atmospheric conditions, reveals the high importance of unraveling the chemical pathways influencing its inner and outer pollutants. Fresh plumes, close to the fire source, typically exhibit high temperatures and rapid reactions. In contrast, aged plumes differ in composition due to shifts in chemical regimes. The presence of sunlight influences oxidative reactions, while its absence favors oxidation paths driven by NO x chemistry. The complexity of fire plume chemistry presents challenges in efficient characterization of species formation and decomposition. It also directly influences gas‐phase species chemical pathways, in‐plume evolution and formation of secondary air pollutants, as well as particulate matter composition and fate. This review provides a detailed description of the chemical mechanisms and pathways inside fresh and aged fire plumes and discusses the implications of critical parameters influencing plume composition. Main tracers are identified, and key processes are described, with information reviewed from laboratory, field, and satellite studies. Unaddressed aspects and emerging opportunities are discussed to provide potential future directions of investigation.
Abstract Concerted exploration and a ten‐fold increase in Martian meteorites reveal a mostly ancient (>4 Ga), lithologically diverse mafic crust (igneous SiO 2 ranging from ∼40%–70%), commonly exhibiting alkaline affinities and with felsic compositions restricted to ancient crust. Most crustal growth (∼80%) took place during the pre‐Noachian, resulting from magma ocean processes. Later crustal additions continued at diminishing rates to the latest Amazonian (<200 Ma). Data from the first fully operational seismometer (InSight mission) indicate the crust is 49 7 km thick on average (∼4 1% of the primitive mantle), with an intracrustal discontinuity, of possible global extent, at about 20–30 km depth. InSight results also suggest a ∼150 km‐thick molten silicate layer (MSL) at the base of the mantle, a possible remnant of the early magma ocean. The MSL represents a distinctive, incompatible (including heat producing) element‐enriched geochemical reservoir, comparable in physical size to the crust. A model for Martian crustal composition indicates a mildly incompatible and heat‐producing element‐enriched basaltic composition (e.g., SiO 2 = 48%, K 2 O = 0.5%, La N /Yb N ∼ 1.8) that becomes less incompatible element‐enriched over geological time. The petrological nature of the crust likely varies in a complex way with depth that may explain the intracrustal seismic discontinuity. The crust contains ∼45 10% of the most incompatible elements in the primitive mantle and this composition is consistent with a mass balance model among crust, MSL, “depleted” mantle and primitive mantle. A geodynamic model for Mars can be constructed that is consistent with geophysical and geochemical constraints currently available.
Abstract River sand and gravel are mined worldwide at volumes that now rival their natural replenishment, yet quantitative knowledge of this mining activity and its consequences lags far behind many other global environmental pressures. We synthesize 411 peer‐reviewed studies published since 1974 within a new Driver‐to‐Management Pathway for Sustainable Sand and Gravel Mining framework that links socio‐economic demand, spatial‐temporal extent of extraction, hydrogeomorphic change, socio‐ecological disruption, and management response. Evidence shows a pronounced scale mismatch: regional‐to‐global drivers fuel largely unreported local extraction, while impacts propagate well beyond mining sites. In most documented cases, annual removal exceeds bed‐material supply several‐fold, producing channel incision, bank collapse, declining groundwater tables, deteriorating water quality, and inland migration of saline water in coastal areas. These physical changes cascade into habitat loss, infrastructure damage, and livelihood insecurity, especially across rapidly developing regions of Asia and Africa. Despite the proliferation of impact studies (69% of the literature), research is dominated by hydrogeomorphic perspectives, with ecological and socio‐economic impacts far more often treated as secondary or co‐occurring components rather than primary foci; meanwhile, only 27% of studies quantify extraction extent and 24% analyze demand drivers, hampering the design of effective interventions. Together, these findings highlight the need for basin‐scale monitoring, cross‐boundary governance, and demand‐side interventions that explicitly link extraction limits to sediment budgets.
