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Earth Day Connections: NASA Investigates Vegetation

In Brief:

From the vantage point of space, NASA’s fleet of Earth-observing satellites investigates connections between ecosystems that are continents apart, or right next door.

Part II

From the vantage point of space, NASA’s fleet of Earth-observing satellites joins with those of partner interagency and international agencies to investigate and illuminate connections between ecosystems that are continents apart, or right next door. With a global perspective, scientists can observe how factors like deforestation, climate change and disasters impact forests and other plant life – while also studying how changes in vegetation impact air quality, waterways and the climate. Vegetation is the primary energy source for nearly all life on Earth, so monitoring it and forecasting how it could be impacted by climate change is key.

In the Amazon, NASA Earth scientists monitor forests and bring these data into the hands of local decision-makers. NASA data provides information about the clearing of trees for agriculture and ranching as well as the impacts of drought on tree mortality. People cut down forests and then ignite the piles of trees and other vegetation, leading to wildfires, which can be detected by instruments including the thermal imager on the Suomi NPP satellite. In 2020, these sensors detected where 1.4 million fires took place. The fires generate smoke that can drift over the continent and be seen from space.

With instruments that collect images of Earth’s surface, researchers can also track the scale of those fires and forest clearings over the years, and even over decades. With the joint NASA/U.S. Geological Survey’s Landsat mission, which launched its first satellite in 1972 and is scheduled to launch Landsat 9 in September 2021, scientists can track changing patterns of deforestation that tells them how Amazonian agricultural practices have changed, from small family holdings to massive ranching operations.

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The Amazon is the largest tropical rainforest in the world, nearly as big as the continental United States. But every year, less of that forest is still standing. Today's deforestation across the Amazon frontier is tractors and bulldozers clearing large swaths to make room for industrial-scale cattle ranching and crops. Landsat satellite data is used to map land cover in Brazil with a historical perspective, going back to 1984. Credit: NASA's Goddard Space Flight Center

Tracking Plant Health from Space

Satellites can detect how “green” an area is – showing the health of plants that are growing in a particular site. While fires, deforestation and drought lead to the tropical Amazon being less green, warming temperatures in the Arctic lead to tundra and boreal regions becoming greener. Using 87,000 Landsat images spanning nearly three decades, scientists found that a third of the land cover of Canada and Alaska looked different in 2012 as compared to 1985. With warmer temperatures, and longer growing seasons, shrubs become denser on grassy tundras, transforming what they looked like from space.

Since plants take up carbon dioxide from the air as they undergo photosynthesis to make food, it may seem that having a greener Arctic would a result in less of the greenhouse gas in the atmosphere. However, a recent study using satellite data and computer models found that any increased carbon uptake in the Arctic is offset by a decline in the tropics. There, warmer global temperatures have led to a drier atmosphere. That means less rainfall and more drought in places like the Amazon, which leads to a drop in tree growth and increases in tree mortality – and less carbon taken from the atmosphere. Soon, water availability could limit the amount of greening in the Arctic as well, the scientists found. As forests expand or are cut back, researchers use data from instruments including MODIS and satellites like Landsat to measure their extent and health.

A new suite of NASA instruments in space also measure the health of forests. The Global Ecosystem Dynamics Investigation – or GEDI – instrument aboard the International Space Station uses lasers to measure the height of trees, allowing researchers to investigate how ecosystems are changing and how the carbon and water cycles are shifting in a warming climate. The Ice, Cloud and land Elevation Satellite 2, or ICESat-2, uses a similar technique to measure heights, and can reach higher latitudes to see changes in the Arctic biomes as well. And the Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station, or ECOSTRESS, measures the temperature of plants, to help determine their water consumption and health.

From Forests to Farms

While climate change impacts the growth and health of vegetation, naturally occurring weather patterns have an impact as well. Scientists with NASA Harvest are looking into the connections between El Niño/La Niña weather patterns, and the farming conditions and crop yields in eastern and southern Africa. During El Niño years, winds and currents in the equatorial Pacific Ocean cause water to pile up against South America, impacting weather patterns around the globe – even in Africa. Researchers found that southern Africa tends to have decreased crop yields during El Niño phases, while eastern Africa sees increased crop yields in those years – knowing these relationships can help farmers and policy makers prepare for a given season.

NASA satellites and science also help farmers in the United States monitor and track their crops. Having more information about rainfall, plant health and other data gives farmers information they use to deal with the extreme weather events that are increasing due to climate change, as well as shifting planting zones and other effects like early freezes and heavier spring rains. The U.S. Department of Agriculture estimates and tracks crop production using farmer surveys and ground observations, with a big-picture assist from Landsat data, NASA computer models and other Earth science resources. They also use MODIS instruments to monitor daily vegetation health – all to help determine what the crop yield will be, and which areas could be facing problems.

These same satellites can also help scientists track the unwanted products of some agricultural fields, including runoff that flows into waterways. Farms, forests, tundra – all these vegetated ecosystems connect to other spheres of our home planet.

Read Part I of this series, 'Earth Day Connections: NASA Study Predicts Less Saharan Dust in Future Winds'

Read Parts III and IV of this series:
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Earth Day Connections: NASA Study Predicts Less Saharan Dust in Future Winds

In Brief:

Temperature and weather systems each interact with, and are influenced by, a multitude of Earth systems, each affected by the warming climate. One of those is the global transport of massive dust plumes from one continent to another.

Part I

During 2020, global average surface temperatures were the hottest on record, tying with 2016 as the warmest recorded year. Last year was also the most active hurricane season to date, with many storms quickly intensifying. Temperature and weather systems each interact with, and are influenced by, a multitude of Earth systems, each affected by the warming climate. One of those is the global transport of massive dust plumes from one continent to another.

In June 2020, a “Godzilla” dust plume travelled from the Sahara, the planet’s largest, hottest desert, across the Atlantic ocean to North America. While this eye-catching plume made headlines, NASA scientists, using a combination of satellite data and computer models, predict that Africa’s annual dust plumes will actually shrink to a 20,000-year minimum over the next century as a result of climate change and ocean warming.

The Sahara Desert is 3,600,000 square miles (9,200,000 square kilometers) of arid land stretched across the northern half of Africa, coming in just slightly smaller in size than the continental United States. Upwards of 60 million tons of its nutrient-laden mineral dust are lifted into the atmosphere each year, creating a massive layer of hot, dusty air that winds carry across the Atlantic to deliver those nutrients to the ocean and vegetation in South America and the Caribbean.

Recent NASA research outlines the domino-like connections between factors beyond the desert’s borders and the development of dust plumes. These start with temperature differences between the North and South Atlantic, which then impact the region’s consistent east to west winds as well as a tropical band of relatively high rainfall located near the Equator, both of which impact the annual dust plumes. Supported by NASA’s Modeling, Analysis, and Prediction (MAP) Program, and its Radiation Sciences Program, the scientists used their new understanding of these relationships to forecast a more substantial reduction in dust activity than previous studies had predicted based on anticipated climate warming.

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Every year millions of tons of dust from the Sahara Desert are swirled up into the atmosphere by easterly trade winds, and carried across the Atlantic. The plumes can make their way from the African continent as far as the Amazon rainforest, where they fertilize plant life. Credit: NASA's Goddard Space Flight Center

A Dusty Past

“From ground observations and satellite observations, we see African dust variability,” said Tianle Yuan, atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. “In fact, it can change quite a bit, from month to month, day to day, year to year, even decade to decade.”

Recent dust estimates are derived from data collected by NASA satellite missions, including Terra, Aqua, and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), a joint mission between NASA and the French space agency, Centre National d'Etudes Spatiales.

The researchers were also interested in seeing if the relationship between global average temperature and Saharan dust activity occurred in the past. Geological records going back thousands of years help reveal past precipitation and nutrient levels as the Sahara went through dramatic environmental shifts.

The peak of Saharan dust transport to the eastern side of the Americas took place roughly between 12,000 to 17,000 years ago, at the end of the last Ice Age. Then began the African Humid Period, during which the vast expanse of desert was speckled with lakes, vegetation, and human habitation. The increased moisture and plant-life stabilized the ground and minimized dust plumes.

“The Sahara Desert was relatively wet back then,” said Yuan. North African sediment cores off the coast and pollen records show that there was more rainfall and vegetation present. “Dust was much rarer.”

Though dust transport has increased since then, the research team found that both natural processes and human activity are now likely driving Earth back toward a dust minimum as climate warms.

Sea surface temperatures directly impact wind speeds, so when the northern Atlantic warms relative to the south Atlantic, the trade winds that blow the dust from east to west become weaker. As a result, the slower winds pick up and transport less dust from the Sahara.

In addition to carrying less dust, the weakened winds also allow the band of steady rain that traverses the tropics to drift north over more of the desert, which dampens the dust and keeps it from getting swept away. Less dust in the air, which can reflect sunshine away from Earth’s surface like a sunshield, means more sunlight and heat reach the ocean, warming it further. All together, this creates a feedback loop of warm sea surface temperatures leading to reduced dust, and reduced dust in turn contributing to additional warming, combining to impact climate, air quality, and storm and hurricane formation.

From Dust to Dust Impacts

“Dust plays a major role in the Earth system,” said Hongbin Yu, an atmospheric researcher at Goddard. “A decrease of dust as the climate warms may have profound influences on a variety of phenomena, but these potential impacts may be good or bad.”

On its journey across the Atlantic, Saharan dust sprinkles into the ocean, feeding the marine life, and similarly plant life once it makes landfall. Minerals like iron and phosphorus in the dust act as a fertilizer for the Amazon rainforest, Earth’s largest and most biodiverse tropical forest. Rains wash many of these valuable nutrients from the soil into the Amazon river basin, making the nutrient delivery from Africa important for maintaining healthy vegetation.

Though African dust transport plays an important role in the genesis of soils and sustaining vegetation, Yu says there are some negative effects because the increase in nutrients can lead to harmful algal blooms off the coast of Florida, and coral reef sicknesses and death linked to dust deposition.

Residents in the Caribbean could also see some benefits as less dust means better air quality. Breathing in dust is particularly hazardous for children, the elderly, and those with respiratory conditions such as asthma. That led a team from NASA Earth Applied Sciences Program to develop an early-warning system for Puerto Rico that now provide three days of lead time before a Saharan dust storm reaches the island, giving doctors and public health officials time to prepare and work with meteorologists on air quality alerts. They use data from the Moderate Resolution Imaging Spectroradiometers (MODIS) on NASA's Terra and Aqua satellites, the Advanced Baseline Imager (ABI) instrument aboard the National Oceanic and Atmospheric Administration (NOAA) Geostationary Operational Environmental Satellite (GOES-16 EAST), and the Visible Infrared Imaging Radiometer Suite (VIIRS) on the joint NASA/NOAA Suomi NPP satellite were employed to help detect the advancing Saharan dust plume before it reached islands like Puerto Rico this past year, so that at-risk communities could prepare for the potentially adverse health effects.

Will the Dust Settle?

“The final piece of the story is looking to the future,” said Yuan. “We want to know what the Sahara dust will be, given the climate change picture we are painting. But directly predicting dust activity is really hard because it involves a lot of processes.”

With projected global warming, the research team used model data from the Coupled Model Intercomparison Project 5 (CMIP5) that indicate at least a 30% reduction in Saharan dust activity from current levels over the next 20 to 50 years, and a continued decline beyond that.

“The minimum humans experienced during the African Humid Period will likely be surpassed because of climate change,” Yuan says of the dust levels during the African Humid Period. As the plumes of dust decline, so will their impacts on vegetation an ocean away.

Media contact:

Ellen Gray
NASA's Earth Science News Team

Read Part II of this series, 'Earth Day Connections: NASA Investigates Vegetation'

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Biden’s moment: What to expect from Thursday’s climate leaders summit

The US is expected to unveil a stronger emissions target and call for higher ambition from big emitters at a leaders’ summit on Thursday

The post Biden’s moment: What to expect from Thursday’s climate leaders summit appeared first on Climate Home News.