Letters in 2019

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.

It has been assumed that spatial patterns of warming are the same under transient and equilibrium scenarios. Analysis of a multi-model ensemble shows that this is not the case, with greater land warming for a transient state, increasing risks that need to be considered in adaptation planning.

Climate change affects the timing of bird migration, which can lead to mismatch with resource availability. Migration occurred earlier in spring and autumn in the United States during the past 24 years; warming led to later arrival in the western Unites States and earlier arrival in the rest of the country.

The Pacific Decadal Oscillation (PDO), a natural climate cycle, alters global climate and influences ecosystems as it varies between positive and negative phases. PDO predictability is reduced under warming as intensified ocean stratification shortens its lifespan and curtails its amplitude.

The risk of concurrent climate extremes affecting breadbasket regions is increasing with climate change, with wheat, maize and soybean crops at risk of simultaneous failure. Correlation between the regions and climate extremes should be considered to ensure food security in the future.

A large-scale meandering in the jet stream can cause simultaneous heat extremes in distant regions. When Rossby waves with wavenumbers 5 and 7 dominate circulation, there is an increased risk of heat extremes across major food-producing regions, raising the potential of multiple crop failures.

Terrestrial primary productivity will increase with CO₂ fertilization, but water limitation will decrease this positive effect. Analyses of Earth system model projections show that extreme droughts will have a much stronger impact on future productivity than mild and moderate droughts.

The ways in which ocean communities respond to warming are related to their composition. The variety of thermal affinities and thermal ranges of individual species, along with vertical temperature gradients, shape community response and allow the prediction of regional responses to warming.

Increased hybridization has the potential to threaten species diversity. Here population genetic computer simulations show that climate-induced adaptive introgression could readily lead to hybridization even when reproductive isolation is independent from climate.

Opinions on climate policy in the United States are politically polarized. Here, survey research shows that opinion polarization on the Green New Deal developed rapidly due to decreasing support among Republicans, which was associated with exposure to conservative media and increasing familiarity with the policy.

Natural peatlands accumulate carbon but land-use change and drainage leads to emission of GHGs from peatlands. Loss of natural peatland area globally has shifted the peatland biome from a sink to a source of carbon, but restoration of drained peatlands could make them carbon neutral.

Nitrous oxide, a strong GHG, is produced during nitrification. Changes in ocean pH cause its production to increase, relative to nitrification rates, suggesting large potential increases in the future as ocean acidification continues.

Permafrost thaw due to rising temperatures will impact soil hydrology in the Arctic. Abrupt changes in soil moisture and land–atmosphere processes may alter the bearing capacity of soil and increase susceptibility to wildfires, with consequences for adapting engineering systems in the region.

Increasingly, financial institutions will be exposed to climate risks that will exacerbate the negative economic impacts of climate change. An agent-based integrated assessment model is used to analyse climate impacts on the global banking system, finding an increase in banking crises and public bailout costs.

Winter warming in the Arctic will increase the CO₂ flux from soils. A pan-Arctic analysis shows a current loss of 1,662 TgC per year over the winter, exceeding estimated carbon uptake in the growing season; projections suggest a 17% increase under RCP 4.5 and a 41% increase under RCP 8.5 by 2100.

Global warming projections exhibit a contracted intertropical convergence zone (ITCZ) and an expanded Hadley cell. Here, equatorial Pacific warming is shown to contract seasonal ITCZ migration and counteract Hadley cell expansion, leading to an equatorward shift in the Asian subtropical monsoon.

Ocean warming and acidification will affect the structure and bioavailability of biomolecules. The toxic form of two neurotoxins will increase with climate change, presenting an ecotoxicology risk with global hotspots as exemplified by saxitoxin toxicity in Alaskan butter clam.

Improved predictions of coral bleaching are critical. In a coordinated global survey effort during the 2016 El Niño, time-series patterns of peak hot temperatures, cool period durations and temperature bimodality were found to be better predictors of coral bleaching than common threshold metrics.

A 30-year dataset shows that marsh plants increased primary productivity and stem density with CO₂ enrichment, but diameter and height decreased under nitrogen limitation. The addition of nitrogen reversed these changes, which is important to allow marshes to keep pace with rising sea levels.

Understanding which factors influence future economic impacts from climate change is important for informing mitigation and adaptation strategies. This study demonstrates that projected economic impacts are primarily attributed to variation in socioeconomic development and future emissions trajectories, rather than uncertainties in the climate response.