Climate change: Potential global threat to city greenery

Up to two-thirds of urban tree species may already be experiencing climate conditions that exceed their safety margins (or potential climatic tolerance), according to a study published in Nature Climate Change. These findings — from the investigation of climate change risk for 3,129 tree and shrub species found across 164 global cities — could help to prioritize efforts to protect urban plants and secure their associated ecosystem services.

Increasing interest has been placed on the vital roles of urban forests in providing services related to human health and well-being, as well as climate control. However, the ability to provide those services relies on the persistence of urban forests in the face of shifting climate regimes.

Manuel Esperon-Rodriguez and colleagues evaluated the climate risk to 3,129 tree and shrub species in 164 cities across 78 countries, under current and future climate conditions. The authors reveal that 56% of species already experience climate conditions that exceed their safety margins for mean annual temperature, while 65% already exceed their safety margin for annual precipitation. Under medium emissions scenarios (RCP6.0, whereby emissions peak around 2080, then decline) by 2050, these numbers are predicted to increase to 76% and 68% of species at risk of predicted changes in mean annual temperature and annual precipitation, respectively. Such predictions are likely conservative, the authors state, as they do not include the additional potential effects of changes in human population and urbanization. Climate risk for urban species is revealed to be particularly high in cities at low latitudes and in countries with high climate change vulnerability and low readiness (as indicated by low Notre Dame Global Adaptation Initiative scores), for example, India, Niger, Nigeria and Togo.

The authors conclude that immediate action is needed to protect global urban forests and prolong the benefits these socioecological systems provide.