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Significance

Pollinators are critical to maintaining terrestrial ecosystem function and the global food supply, but many are in decline. However, we have limited information identifying which species are at elevated extinction risk, limiting efforts to prioritize scarce conservation resources. We assessed the extinction risk of nearly 1,600 species of vertebrate and insect pollinators and found that more than one in five species is at risk of extinction. The major threats are climate change, agriculture, modifications to hydrological and fire regimes, and housing and urban development. These results can inform management actions to help prevent pollinator extinctions.

Abstract

Pollinators are critical for food production and ecosystem function. Although native pollinators are thought to be declining, the evidence is limited. This first, taxonomically diverse assessment for mainland North America north of Mexico reveals that 22.6% (20.6 to 29.6%) of the 1,579 species in the best-studied vertebrate and insect pollinator groups have elevated risk of extinction. All three pollinating bat species are at risk and bees are the insect group most at risk (best estimate, 34.7% of 472 species assessed, range 30.3 to 43.0%). Substantial numbers of butterflies (19.5% of 632 species, range 19.1 to 21.0%) and moths (16.1% of 142 species, range 15.5 to 19.0%) are also at risk, with flower flies (14.7% of 295 species, range 11.5 to 32.9%), beetles (12.5% of 18 species, range 11.1 to 22.2%), and hummingbirds (0% of 17 species) more secure. At-risk pollinators are concentrated where diversity is highest, in the southwestern United States. Threats to pollinators vary geographically: climate change in the West and North, agriculture in the Great Plains, and pollution, agriculture, and urban development in the East. Woodland, shrubland/chaparral, and grassland habitats support the greatest numbers of at-risk pollinators. Strategies for improving pollinator habitat are increasingly available, and this study identifies species, habitats, and threats most in need of conservation actions at state, provincial, territorial, national, and continental levels.

Abstract

Tropical marine low cloud feedback is key to the uncertainty in climate sensitivity, and it depends on the warming pattern of sea surface temperatures (SSTs). Here, we empirically constrain this feedback in two major low cloud regions, the tropical Pacific and Atlantic, using interannual variability. Low cloud sensitivities to local SST and to remote SST, represented by lower-troposphere temperature, are poorly captured in many models of the latest global climate model ensemble, especially in the less-studied tropical Atlantic. The Atlantic favors large positive cloud feedback that appears difficult to reconcile with the Pacific—we apply a Pareto optimization approach to elucidate trade-offs between the conflicting observational constraints. Examining ~200,000 possible combinations of model subensembles, this multi-objective observational constraint narrows the cloud feedback uncertainty among climate models, nearly eliminates the possibility of a negative tropical shortwave cloud feedback in CO2-induced warming, and suggests a 71% increase in the tropical shortwave cloud feedback.

Editor’s summary

As climate has warmed, precipitation and evapotranspiration changes have affected land surface water fluxes. What impact has that had on terrestrial water storage, the amount of water stored on and in the land? Seo et al. combined soil moisture data from satellites, measurements of sea level, and observations of polar motion to estimate terrestrial water storage over the past four decades, which revealed a dramatic decline (see the Perspective by Samaniego). During the interval from 2000 to 2002, terrestrial water storage decreased by nearly twice as much as Greenland ice mass loss over the same period. —Jesse Smith

Abstract

Rising atmospheric and ocean temperatures have caused substantial changes in terrestrial water circulation and land surface water fluxes, such as precipitation and evapotranspiration, potentially leading to abrupt shifts in terrestrial water storage. The European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) soil moisture (SM) product reveals a sharp depletion during the early 21st century. During the period 2000 to 2002, soil moisture declined by approximately 1614 gigatonnes, much larger than Greenland’s ice loss of about 900 gigatonnes (2002–2006). From 2003 to 2016, SM depletion continued, with an additional 1009-gigatonne loss. This depletion is supported by two independent observations of global mean sea level rise (~4.4 millimeters) and Earth’s pole shift (~45 centimeters). Precipitation deficits and stable evapotranspiration likely caused this decline, and SM has not recovered as of 2021, with future recovery unlikely under present climate conditions.