Could urbanisation be good for the climate?

In the last few decades, China has undergone enormous urbanisation. It has been assumed that as forests are cleared to build cities, they release the carbon stored in them, consequently increasing greenhouse gas emissions. However, this is not the case, according to a new study conducted by an international team of researchers. Supported by the EU-funded TOFDRY and CabaKarst projects, the research team has found that, contrary to popular belief, China’s massive population shift from rural to urban areas has had a positive effect on the country’s carbon stocks. Their findings were published in the journal ‘Nature Sustainability’.

Aided by remote sensing technology, the scientists demonstrated that the last two decades of urbanisation have led to an increase in biomass and carbon stocks in China’s rural areas and in its recently developed cities. Despite an initial carbon loss from above-ground biomass of 20 million tonnes between 2002 and 2010, by 2019 there was an overall gain of 30 million tonnes of carbon stored in urban areas thanks to urban greening. “Even though urban growth is to blame for a loss of carbon during the first half of the period, green policy initiatives compensated for the loss and lead to an overall balancing effect. Indeed, a slight surplus in the climate account has been achieved,” states study lead author and PhD student Xiaoxin Zhang of TOFDRY and CabaKarst project coordinator University of Copenhagen (UCPH), Denmark, in a news release posted on ‘ScienceDaily’.The billions of new trees planted in recent decades as part of China’s afforestation strategy is not the only reason for this surplus. “As people move into dense urban areas, they leave large tracts of land behind. This eases pressures on natural vegetation and lets new vegetation absorb carbon. At the same time, the ebb of population from rural areas has provided more space to plant new trees in the countryside,” explains Dr Xiaowei Tong of UCPH.

Tree cover has also grown in China’s cities in the last decade. “There may be plenty of things to criticize China about, but the country is very advanced when it comes [to] incorporating green spaces into urban planning. An increase in carbon sinks in urban areas during recent years is very likely the result of an active urban greening policy. This compensates for the CO2 released as trees and plants are cleared for urban development,” notes study co-author Prof. Rasmus Fensholt of UCPH, adding that “urbanization can be an integral component of a recipe for reducing CO2 emissions, if urban development is designed to be sufficiently green.”

However, the study supported by TOFDRY (Trees outside forests in global drylands) and CabaKarst (Between degradation and conservation: The carbon balance of the Chinese karst ecosystem) warns that current efforts are not enough for China to meet its goal of climate neutrality by 2060. “There is a limit as to how much and for how long trees can suck up CO2. At some point, a mature forest will completely stop capturing carbon. Thus, if China wants to be climate neutral, planting more trees won’t be enough. For this reason, it is crucial for them to drastically reduce emissions from fossil fuels. Nevertheless, in this study we observed what could be called a kickstart of their green transition,” observes Prof. Fensholt.

For more information, please see:

TOFDRY project website

CabaKarst project