Volume 10 Issue 2, 2 February 2020

Framing solutions to climate change as natural strongly influences their acceptability, but what constitutes a ‘natural’ climate solution is selected, not self-evident. We suggest that the current, narrow formulation of natural climate solutions risks constraining what are thought of as desirable policy options.

For years, halogens have been known as destroyers of ‘good’ ozone, which acts as an upper-atmosphere shield from harmful ultraviolet radiation. Research now shows that natural halogen compounds emitted from the ocean help to control ‘bad’ ozone pollution at ground level and may continue to do so at a similar rate in future climate.

The impacts of climate change on the ecohydrology of forested mountain regions are uncertain. New high-resolution modelling suggests that during a hot, dry summer in the Alps, stressed vegetation capitalizes on downslope water subsidies, amplifying runoff deficits and further depleting water resources.

Ground-level ozone is an air pollutant that is harmful to human health, as well as to plants, trees and crops. New analyses based on Earth system modelling show that reducing ozone from the energy, industrial and transportation sectors could mitigate climate change by enhancing the ability of vegetation to remove carbon dioxide from the atmosphere through photosynthesis.

As tundra ecosystems respond to rapid Arctic warming, satellite records suggest a widespread greening. This Perspective highlights the challenges of interpreting complex Arctic greening trends and provides direction for future research by combining ecological and remote sensing approaches.

The rapid growth of climate change research presents challenges for IPCC assessments and their stated aim of being comprehensive, objective and transparent. Here the authors use topic modelling to map the climate change literature, and assess how well it is represented in IPCC reports.

The relative roles of local and remote processes in determining equatorial warming are still debated. Model simulations show that coupled feedbacks strongly damp the equatorial surface temperature response to local equatorial forcing, while amplifying the response to remote off-equatorial forcing.

Arctic warming is attributed to GHGs and feedbacks, but the specific contribution of ozone-depleting substances (ODS)—also potent GHGs—has never been quantified. Here, model simulations suggest ODS contributed 0.8°C of Arctic warming and led to considerable sea-ice loss during the period 1955–2005. [This summary has been amended to reflect the addendum published 28 January 2020]

Ozone forms in the atmosphere when other anthropogenically emitted gases react with sunlight and negatively impacts terrestrial gross primary productivity (GPP). Reducing emissions of ozone precursors by 50%, particularly in the road transportation and energy sectors, could increase GPP by 750 TgC yr^–1.

N₂O emissions from rivers have increased globally by a factor of four between 1900 and 2016, with emissions starting to decline since the early 2000s. Most riverine N₂O emissions come from smaller streams, driven primarily by the use of nitrogen fertilizers in agriculture.

Crustose coralline algae help build coral reef structures through calcification, a process threatened under ocean acidification. Juvenile algae were highly sensitive on initial exposure to ocean acidification, but continued exposure over six generations showed a gain of tolerance.

An Earth system model estimates that natural halogens, of marine biotic and abiotic origin, remove about 13% of present-day global tropospheric O₃. Projections suggest this ratio is stable through 2100, with high spatial heterogeneity, despite increasing natural halogens.

Mountain forest drought can paradoxically increase evapotranspiration (green water), helping vegetation at the expense of runoff (blue water). This is quantified for the 2003 event in the European Alps, highlighting underappreciated vulnerability of blue-water resources to future warmer summers.

Changes in ocean temperature and pH will impact on species, as well as impacting on community interactions. Here warming and acidification cause a clam species to change their feeding mode, with cascading effects for the marine sedimentary food web.