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Accelerating the Green Transition
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By NASA
As any urban dweller who has lived through a heat wave knows, a shady tree can make all the difference. But what happens when there’s no shade available?
A recent study in Nature Communications used NASA satellite data to identify a major gap in global resilience to climate change: cities in the Global South have far less green space — and therefore less cooling capacity — than cities in the Global North. The terms Global North and Global South were used in the study to distinguish developed countries (mostly in the Northern Hemisphere) from developing nations (mostly in the Southern Hemisphere).
Cities tend to be hotter than nearby rural areas because of the urban heat island effect. Heat-trapping dark surfaces such as sidewalks, buildings, and roads absorb heat from the Sun’s rays, which raises the temperature of the city. Extreme heat poses serious health threats for urban residents, including dehydration, heat stroke, and even death. Though not a cure-all, greenery provides shade and releases moisture into the air, cooling the surroundings.
“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 who was not affiliated with this study. “Satellite data can be really helpful for this.”
The Operational Land Imager (OLI) on the NASA and U.S. Geological Survey’s Landsat 8 satellite captured this natural color image of Sanaa, Yemen, on June 8, 2024. Sanaa, which has a hot, dry climate and little green space, had the second-lowest cooling capacity of 500 cities studied in a paper recently published in the journal Nature Communications. Wanmei Liang, NASA Earth Observatory An international team of researchers led by Yuxiang Li, a doctoral student at Nanjing University, analyzed the 500 largest cities in the world to compare their cooling capacities. They used data from the Landsat 8 satellite, jointly managed by NASA and the U.S. Geological Survey, to determine how effective green space was at cooling each city.
First, they calculated the average land surface temperature for the hottest month of 2018 for each city, as well as the average of the hottest months from 2017 to 2019. Next, the researchers used a metric called the Normalized Difference Vegetation Index (NDVI) to map how much green space each city had. The NDVI relies on the fact that healthy vegetation absorbs red light and reflects infrared light: the ratio of these wavelengths can show the density of healthy vegetation in a given satellite image.
Researchers found that cities in the Global South have just 70% of the greenery-related cooling capacity of cities in the Global North. The green spaces in an average Global South city cool the temperature by about 4.5 F (2.5 C). In an average Global North city, that cooling capacity is 6.5 F (3.6 C). This compounds an existing problem: cities in the South tend to be at lower latitudes (that is, nearer to the Equator), which are predicted to see more heat extremes in the coming years.
“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. The Global South has less capacity to adapt to heat because air conditioning is less common and power outages are more frequent.
Why do cities in the Global South struggle to stay cool? Cities in the Global South tend to have less green space than cities in the Global North. This mirrors studies of the disparities within cities, sometimes referred to as the “luxury effect”: wealthier neighborhoods tend to have more green space than poorer neighborhoods. “Wealthier cities also have more urban green spaces than the poorest cities,” Chi said.
It’s unlikely that urban planners can close the gap between the study’s worst-performing city (Mogadishu, Somalia) and the best-performing one (Charlotte, North Carolina).
Mogadishu is a dense city with a dry climate that limits vegetation growth. Still, there’s a lot that each city can learn from its neighbors. Within a given region, the researchers identified the city with the greatest cooling capacity and used that as a goal. They calculated the difference between the best-performing city in the region and every city nearby to get the potential additional cooling capacity. They found that cities’ average cooling capacity could be increased substantially — to as much as 18 F (10 C) — by systematically increasing green space quantity and quality.
“How you utilize green space is really going to vary depending on the climate and the urban environment you’re focused on,” said Braneon, whose research at NASA focuses on climate change and urban planning.
Greener cities in the U.S. and Canada have lower population densities. However, fewer people per square mile isn’t necessarily good for the environment: residents in low-density cities rely more on cars, and their houses tend to be bigger and less efficient. Braneon noted that there’s a suite of solutions beyond just planting trees or designating parks: Cities can increase cooling capacity by creating water bodies, seeding green roofs, and painting roofs or pavement lighter colors to reflect more light.
With a global study like this, urban planners can compare strategies for cities within the same region or with similar densities. “For newly urbanized areas that aren’t completely built out, there’s a lot of room to still change the design,” Braneon said.
By Madeleine Gregory
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Nov 26, 2024 Editor Rob Garner Contact Rob Garner rob.garner@nasa.gov Location Goddard Space Flight Center Related Terms
Climate Change Earth Goddard Institute for Space Studies Goddard Space Flight Center Landsat Landsat 8 / LDCM (Landsat Data Continuity Mission) View the full article
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By Space Force
U.S. Space Force and U.S. Space Operations Command have transitioned two additional Space Deltas to fully-integrated Mission Deltas under the Unified Mission Readiness concept, marked by ceremonies Oct. 30-31, 2024.
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By NASA
Mars: Perseverance (Mars 2020) Perseverance Home Mission Overview Rover Components Mars Rock Samples Where is Perseverance? Ingenuity Mars Helicopter Mission Updates Science Overview Objectives Instruments Highlights Exploration Goals News and Features Multimedia Perseverance Raw Images Images Videos Audio More Resources Mars Missions Mars Sample Return Mars Perseverance Rover Mars Curiosity Rover MAVEN Mars Reconnaissance Orbiter Mars Odyssey More Mars Missions The Solar System The Sun Mercury Venus Earth The Moon Mars Jupiter Saturn Uranus Neptune Pluto & Dwarf Planets Asteroids, Comets & Meteors The Kuiper Belt The Oort Cloud 2 min read
Red Rocks with Green Spots at ‘Serpentine Rapids’
NASA’s Mars Perseverance rover acquired this image, a nighttime mosaic of the Malgosa Crest abrasion patch at “Serpentine Rapids,” using its SHERLOC WATSON camera, located on the turret at the end of the rover’s robotic arm. The diameter of the abrasion patch is 5 centimeters (about 2 inches) and the large green spot in the upper center left of the image is approximately 2 millimeters (about 0.08 inch) in diameter. Mosaic source images have been debayered, flat-fielded, and linearly color stretched. This image was acquired on Aug. 19, 2024 (sol 1243, or Martian day 1,243 of the Mars 2020 mission) at the local mean solar time of 19:45:30. NASA/JPL-Caltech After discovering and sampling the “leopard spots” of “Bright Angel,” it became apparent that Perseverance’s journey of discovery in this region was not yet finished. Approximately 20 sols (Martian days) after driving south across Neretva Vallis from Bright Angel, the rover discovered the enigmatic and unique red rocks of “Serpentine Rapids.”
At Serpentine Rapids, Perseverance used its abrading bit to create an abrasion patch in a red rock outcrop named “Wallace Butte.” The 5-cm diameter abrasion patch revealed a striking array of white, black, and green colors within the rock. One of the biggest surprises for the rover team was the presence of the drab-green-colored spots within the abrasion patch, which are composed of dark-toned cores with fuzzy, light green rims.
On Earth, red rocks — sometimes called “red beds” — generally get their color from oxidized iron (Fe3+), which is the same form of iron that makes our blood red, or the rusty red color of metal left outside. Green spots like those observed in the Wallace Butte abrasion are common in ancient “red beds” on Earth and form when liquid water percolates through the sediment before it hardens to rock, kicking off a chemical reaction that transforms oxidized iron to its reduced (Fe2+) form, resulting in a greenish hue. On Earth, microbes are sometimes involved in this iron reduction reaction. However, green spots can also result from decaying organic matter that creates localized reducing conditions. Interactions between sulfur and iron can also create iron-reducing conditions without the involvement of microbial life.
Unfortunately, there was not enough room to safely place the rover arm containing the SHERLOC and PIXL instruments directly atop one of the green spots within the abrasion patch, so their composition remains a mystery. However, the team is always on the lookout for similar interesting and unexpected features in the rocks.
The science and engineering teams are now dealing with incredibly steep terrain as Perseverance ascends the Jezero Crater rim. In the meantime, the Science Team is hanging on to the edge of their seats with excitement and wonder as Perseverance makes the steep climb out of the crater it has called home for the past two years. There is no shortage of wonder and excitement across the team as we contemplate what secrets the ancient rocks of the Jezero Crater rim may hold.
Written by Adrian Broz, Postdoctoral Scientist, Purdue University/University of Oregon
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Last Updated Oct 25, 2024 Related Terms
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