290 million new city dwellers benefit China's climate balance

Date:
February 22, 2022
Source:
University of Copenhagen - Faculty of Science
Summary:
Contrary to popular belief, China's massive emigration from rural
areas to cities has been shown to have a positive effect on China's
carbon stocks. Urbanization can even play a role in attaining
climate neutrality. This is the conclusion of researchers based
upon analyses of vast amounts of satellite data.



FULL STORY ========================================================================== Contrary to popular belief, China's massive emigration from rural areas to cities has been shown to have a positive effect on China's carbon stocks.

Urbanization can even play a role in attaining climate neutrality. This
is the conclusion of University of Copenhagen researchers based upon
analyses of vast amounts of satellite data.


========================================================================== Urbanization is an explosive trend across most of the planet. Nowhere has rural-urban migration transpired at such a massive scale as in China,
where more than 290 million people have relocated to cities over the
last three decades.

Urbanization is generally perceived as a trend that comes with increased greenhouse gas emissions. The assumption is that as forests, which
sequester carbon, are cleared to make room for urban growth, the carbon
stored in them is released and CO2 emissions increase.

However, with the help of remote sensing technology that uses satellite observations to map natural resources, researchers from the University
of Copenhagen have now rejected that assumption. To the contrary, their
study demonstrates that the past two decades of urbanization in China
has resulted in an increase in biomass and carbon stocks, both in rural
areas and recently developed cities. The findings were published in the
journal Nature Sustainability.

"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," explains the study's lead author,
PhD student Xiaoxin Zhang, of the University of Copenhagen's Department
of Geosciences and Nature Management.

From 2002-2010, China's urban areas experienced carbon loss from
aboveground biomass equivalent to 20 million tons. However, the combined
carbon balance from 2002-2019 ended up at a gain of 30 million tons of
carbon in urban areas.

China's total aboveground carbon stocks grew by 290 million tons per year.



==========================================================================
From large to small areas China's afforestation strategy has resulted in billions of new trees in recent decades and thereby played a key role in
the country's carbon balance. However new plantations of forest don't
explain everything: "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," says postdoctoral researcher Xiaowei Tong of UCPH's Department of Geosciences
and Natural Resource Management The growth of parks and green spaces
Tree cover has grown in cities over the past decade as well. The Chinese government's ecological civilization policy has ensured for a certain percentage of urban parks, trees, green roofs, vertical gardens and
the like.



========================================================================== "There may be plenty of things to criticize China about, but the country
is very advanced when it comes 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," says Professor Rasmus Fensholt of the Department of Geosciences and Natural Resource Management.

He adds: "It even suggests that urbanization can be an integral component
of a recipe for reducing CO2 emissions, if urban development is designed
to be sufficiently green." Minimal encroachment on forests and farmland
The analyses also demonstrate that the growing pains of cities have had
very little impact on the country's forests. Only 6% of urban expansion
has come at the expense of forested land. Instead, new development
has primarily replaced agricultural land (81%) and grasslands (10%) --
types of vegetation that have low carbon storage potential compared to
tree cover.

Despite cities having made the biggest inroads into agricultural land,
China's agricultural area has only shrunk by 3.8% during the period. For
the most part, this is probably due to the intensification of agriculture
and increased food imports.

"There is a narrative that increasing urbanization simply destroys large
tracts of vegetation and replaces greenery with concrete and asphalt. We demonstrate that this is not the case in China," says Martin Brandt,
an assistant professor at the Department of Geosciences and Natural
Resource Management.

Tree planting isn't enough If China is to achieve its goal of climate neutrality by 2060, the researchers point out that planting trees won't suffice: "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,"
explains Professor Fensholt.

"All in all, our data from China shows that you can expand cities while at
the same time increasing your carbon capture if the right conditions are established. This could serve as an inspiration to low-income countries
wanting to improve their climate footprint and overall environmental conditions," says Martin Brandt.

The researchers underscore that the study results are composed of
significant components, but not the entire equation for China's climate footprint in urban areas. Among other things, the footprint of food
imports is not accounted for.

The researchers primarily used 'Remote Sensing' technology, where time
series of satellite images of China's tree cover were used to estimate the development of biomass. They also used demographics and population density data. Finally, using mobile phone log data and satellite observations
of nighttime light, the researchers were able to calculate whether the proportion of the Chinese population registered in rural areas actually
lives in cities.

ABOUT THE STUDY
* Demographic data shows that the rural population of China
increased by
3.59 million people annually between 1990 and 1995. In 1995,
859 million Chinese lived in rural areas. By 2020, the figure was
510 million.

* Over the same period, the urban population grew from 301 million
(26.41%)
in 1990 to 848 million (63.89%) in 2020. China's urban population
exceeded its rural population for the first time in 2011.

special promotion Explore the latest scientific research on sleep and
dreams in this free online course from New Scientist -- Sign_up_now_>>> ========================================================================== Story Source: Materials provided by University_of_Copenhagen_-_Faculty_of_Science. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Xiaoxin Zhang, Martin Brandt, Xiaowei Tong, Philippe Ciais,
Yuemin Yue,
Xiangming Xiao, Wenmin Zhang, Kelin Wang, Rasmus Fensholt. A large
but transient carbon sink from urbanization and rural depopulation
in China.

Nature Sustainability, 2022; DOI: 10.1038/s41893-021-00843-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220222135235.htm

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