Volume 11 Issue 9, September 2021

Climate extremes dominate headlines around the world as the IPCC releases its physical climate assessment report.

Climate services have long sought to bridge the gap between climate science and improved societal decision-making. Now, a study finds that fulfilling that promise will require rethinking the norms, institutions and governance of science itself.

Economically optimal climate strategies may be politically less feasible because they need strong collective action. Fortunately, achieving climate goals through more realistic differentiated policies may not be much more expensive.

Climate models disagree on how the year-to-year variability of the El Niño/Southern Oscillation will change in a warmer world. Using a high-resolution climate model with an improved tropical Pacific mean state, research now suggests that El Niño activity tends to get weaker under GHG-induced warming.

Changes in river discharge due to climate change are highly uncertain, and a recent study used a global streamflow dataset to assess whether such trends are detectable. Streamflow changes occurred more often in basins impacted by human disturbances than in pristine ones, and there was no clear signal from climate change alone.

Observational data from long-term monitoring plots show that the carbon sink of remaining, undisturbed African and Amazonian tropical rainforest is declining. A study now finds that simulations from Earth system models cannot reproduce this decline.

As climate change impacts marine ecosystems, fish must migrate or adapt and eventually speciate to preserve their diversity. Research now shows that warming has coincided with reduced fish body size throughout evolutionary history, hindering both preservation strategies.

Climate services aim to make climate data and information accessible for climate-sensitive decision-making. However, the grounding of climate services in the norms and institutions of climate science creates tensions that reduce the impact of climate services.

The nationwide cost of cutting emissions can be affected by local policies. This study considers the differences across the US states, with integrated assessment model results showing that varying state policies only increases nationwide costs by about 10%.

Combining previous estimates in a multimethod approach, extreme sea levels are assessed under global warming levels of 1.5–5 °C at over 7,000 coastal sites worldwide. By 2100 or before, about 50% of locations exhibit present-day 100-year extreme sea levels at least once per year, even at 1.5 °C of warming.

The impact of climate warming on El Niño/Southern Oscillation (ENSO) amplitude is uncertain in centennial-scale model projections due to internal variability, but an ensemble of millennial-scale simulations suggests decreased ENSO amplitude in the equilibrium response to greenhouse gas forcing.

High-resolution climate models exhibit reduced tropical Pacific mean-state biases due to better representation of ocean mesoscale processes, like tropical instability waves. With climate warming, these improved dynamics project weaker El Niño/Southern Oscillation sea surface temperature variability.

Climate change may result in larger releases of CH₄ than CO₂ from wetlands as CH₄ emissions seem to be more sensitive to temperature. Globally, CO₂ and CH₄ emissions show a similar temperature dependence but this is modulated by wetland water table depth, which affects CH₄ (but not CO₂) emissions.

The authors show increased negative extremes in gross primary productivity in northern midlatitude ecosystems, particularly over grasslands and croplands, attributed to impacts of warm droughts. This highlights the vulnerability of terrestrial carbon sinks and food security to increasing extreme events.

The authors investigate temperature and pH effects on fitness of an abundant marine crustacean (copepod) across 25 generations. Reduced fitness under combined warming and acidification was recovered rapidly, but incompletely, due to interactions between warming and acidification effects.

Phylogenetic data over the past ~150 million years show smaller fish occurred in warmer waters, moved shorter distances at low speed and had low speciation rates. Fish moved faster and evolved quicker under periods of rapid change, with implications for movement and survival under climate change.