Volume 10 Issue 8, 2 August 2020

Planned relocation of communities exposed to climate hazards is an important adaptation measure. However, relocation planning and policies must recognize and support those who do not wish to relocate, particularly groups with strong place attachment and for whom relocation may increase, not reduce, vulnerability.

Phasing out coal requires expanding the notion of a ‘just transition’ and a roadmap that specifies the sequence of coal plant retirement, the appropriate policy instruments as well as ways to include key stakeholders in the process.

Over the last two decades, many countries have passed laws addressing climate change and related areas. Research now shows that these laws make a difference to emission outcomes, but the pathways of impact require further research.

Over the last half of the twentieth century, surface temperature over the South Pole was steady if not slightly cooling, suggesting the high Antarctic interior might be immune to warming. Research now shows a dramatic switch; in the past 30 years, the South Pole has been warming at over three times the global rate.

Warming can change the vegetation growing season, but the response of autumn phenology to warming remains uncertain. Now research shows warming can lead to autumn greening by delaying leaf senescence, but carbon uptake is constrained by radiation.

In recent decades, the Arctic has warmed at over twice the global rate. This Perspective places these trends into the context of abrupt Dansgaard–Oeschger warming events in the palaeoclimate record, arguing that the contemporary Arctic is undergoing comparably abrupt climate change.

Large-scale mechanisms causing regional drying are not well understood. Models and observational data reveal that human-caused changes in GHGs and aerosols led to detectable global and hemispheric signals in the joint behaviour of precipitation, temperature and aridity since the 1950s.

Polar bear numbers are expected to decline as the sea ice they rely on to catch their prey declines with global warming. Projections show when fasts caused by declining sea ice are likely to lead to rapid recruitment and survival declines across the polar bear circumpolar range.

Phenological shifts due to warming extend the growing season for plants, with implications for ecosystem productivity. Carbon uptake through photosynthesis is limited by radiation, particularly in autumn, which explains contrasting regional responses of autumn carbon uptake to rising temperatures.

Carbon dioxide removal technologies may be needed to meet climate targets. In this study, national surveys and deliberative workshops in the United States and the United Kingdom show that carbon dioxide removal is perceived as too slow to address the immediate climate crisis while not addressing the root causes of climate change.

Climate change laws are shown to reduce national CO₂ emissions by 0.78% in their first three years and 1.79% in the longer term. These reductions add up to 38 GtCO₂ of avoided emissions for 1999–2016—equal to a year of CO₂ emissions.

A large proportion of anthropogenic heat energy is being taken up by ocean warming. Analysis of yearly 0–700 m ocean heat content maps from four different estimates shows that the longer the period over which regional trends are estimated, the larger the area of statistically significant warming.

Surface air temperatures at the South Pole warmed at over three times the global rate in recent decades. Research shows this trend was driven remotely by the tropics and locally by a positive phase of the Southern Annular Mode, increasing the influx of warm moist air atop anthropogenic warming.

Climate change has altered the vertical structure of atmospheric temperature. Global land observations show melting level height (the altitude where falling precipitation begins to melt) has increased, deepening the warm cloud layer and intensifying rainfall extremes at the expense of snow and hail.

Autumn leaf senescence has later onset, higher phenological plasticity and a stronger climatic response under warm compared to cold autumns. While night-time warming delays senescence, drought induced by daytime warming advances it, which may lead to loss in growing season under global warming.

The economic optimality of limiting global warming to below 2 °C has been questioned. This analysis shows that the 2 °C target is economically optimal in a version of the DICE model that includes updated climate science, climate damage estimates and evidence on social discount rates.