NASA on Combating Climate Change: Establish Green Spaces in Cities

A new study published in Nature Communications used data from NASA satellites to suggest a method for increasing cities’ cooling capacity: Establish more green spaces. The study found that green spaces in cities could absorb carbon, provide shade, and reduce temperatures in those cities.

The study compared cities in the Global North, which tend to have more green spaces, with similar cities in the Global South which had less green space. Most cities featured in the study tended to be hotter than rural areas due to the urban heat island effect caused by the increased density of artificial elements like sidewalks, roads, and buildings that replaced green areas. These elements tend to be darker and absorb more heat.

“Cities can strategically prioritize developing new green spaces in areas that have less green space,” said Christian Braneon, a climate scientist at NASA’s Goddard Institute for Space Studies in New York. While Braneon did not participate in the study, he highlighted the value of satellite data for studies like this.

The international team of scientists led by Nanjing University doctorate student Yuxiang Li used data from Landsat 8 for this study. NASA and the U.S. Geological Survey jointly manage Landsat 8, which can collect data in visible light and infrared. Originally launched in 2013, it was meant to have an operational life of 5 years and is still functional.

The team used data collected by Landsat 8 during the hottest months of 2017, 2018, and 2019 to calculate the average land surface temperature for those months. Then they compared it to the Normalized Difference Vegetation Index (NDVI) for each city. The NDVI uses plants’ ability to absorb red light and reflect infrared to determine the amount of healthy vegetation in a satellite image.The below video demonstrates the ways that satellites can track information about urban heat islands, flooding, and canopy cover, for instance.

They found that cities in the Global South had 70% of the vegetation that similar cities in the Global North have. The Global South had an average cooling capacity that was 1.1 degrees Celsius less than cities in the Global North (2.5 C in the South, compared to 3.6 C in the North). The Global South consists mostly of developing regions in the southern hemisphere. The Global North consists of more developed regions of the northern hemisphere.

“It’s already clear that Global South countries will be impacted by heat waves, rising temperatures, and climatic extremes more than their Global North counterparts,” said Chi Xu, a professor of ecology at Nanjing University and a co-author of the study.

Complicating the situation, power outages are more common and air conditioning is less common in the Global South. Because poorer regions tend to have less green space than wealthier regions, incentivizing the development of more green space could include planting more fruit trees and creating space for community vegetable gardens. Other solutions could include painting the tops of buildings in lighter colors or even establishing “rooftop gardens” on buildings with flat rooftops.

Previous studies showed that urban city gardens could help cool cities down. University of Delaware undergraduate researcher Ryan DeRosa took a closer look at the optimal garden compositions and foliage could provide the best cooling effect, for instance, as seen in the below video:

Improved infrastructure like a more reliable power grid and better transportation-related infrastructure could also help improve conditions. Better public transportation and more support for alternative transportation options like walking or bicycling could also be an option in cities with more urban sprawl to reduce the need to add more traffic lanes to heavily used roads. Some countries like India have been working on improving their power grid, especially in regions with more poverty.

The researchers did note that climate and population could be a challenge. The city with the least green space, Mogadishu, Somalia, has a hot, dry climate and dense population that can limit its ability to grow more vegetation.

Cities with lower population densities could still improve their green spaces to reduce temperatures. NASA highlighted its capacity to track important environmental components like green spaces in cities using data from satellites like Landsat 8. This not only established the importance of green spaces for helping keep cities cool but could also help track progress in developing green spaces for cities that could still rethink their approach to urban planning.