Changing colors of our living planet
KARACHI:A NASA report says life is the one thing that, so far, makes Earth unique among the thousands of other planets we’ve discovered. Since the fall of 1997, NASA satellites have continuously and globally observed all plant life at the surface of the land and ocean. During the week of Nov. 13-17, NASA is sharing stories and videos about how this view of life from space is furthering knowledge of our home planet and the search for life on other worlds.
NASA satellites can see our living Earth breathe. In the Northern Hemisphere, ecosystems wake up in the spring, taking in carbon dioxide and exhaling oxygen as they sprout leaves — and a fleet of Earth-observing satellites tracks the spread of the newly green vegetation.
Meanwhile, in the oceans, microscopic plants drift through the sunlit surface waters and bloom into billions of carbon dioxide-absorbing organisms — and light-detecting instruments on satellites map the swirls of their color. This fall marks 20 years since NASA has continuously observed not just the physical properties of our planet, but the one thing that makes Earth unique among the thousands of other worlds we’ve discovered: Life.
Satellites measured land and ocean life from space as early as the 1970s. But it wasn’t until the launch of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) in 1997 that the space agency began what is now a continuous, global view of both land and ocean life. A new animation captures the entirety of this 20-year record, made possible by multiple satellites, compressing a decades-long view of life on Earth into a captivating few minutes.
“These are incredibly evocative visualizations of our living planet,” said Gene Carl Feldman, an oceanographer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That’s the Earth, that is it breathing every single day, changing with the seasons, responding to the Sun, to the changing winds, ocean currents and temperatures.”
Sixty years ago, people were not sure that Earth’s surface could be seen clearly from space. Many thought that the dust particles and other aerosols in the atmosphere would scatter the light, masking the oceans and continents, said Jeffrey Masek, chief of the Biospheric Sciences Laboratory at NASA Goddard.
The Gemini and Apollo programs demonstrated otherwise. Astronauts used specialized cameras to take pictures of Earth that show the beauty and complexity of our living planet, and helped kickstart the era of Earth science research from space. In 1972, the first Landsat mission began its 45-year record of vegetation and land cover. “As the satellite archive expands, you see more and more dynamics emerging,” Masek said. “We’re now able to look at long-term trends.”
The grasslands of Senegal, for example, undergo drastic seasonal changes. Grasses and shrubs flourish during the rainy season from June to November, then dry up when the rain stops. With early weather satellite data in the 1970s and ’80s, NASA Goddard scientist Compton Tucker was able to see that greening and die-back from space, measuring the chlorophyll in the plants below. He developed a way of comparing satellite data from two wavelengths, which gives a quantitative measurement of this greenness called the Normalized Difference Vegetation Index.
“We were astounded when we saw the first images. They were amazing because they showed how vegetation changed annually, year after year,” Tucker said, noting that others were surprised as well when the study came out in 1985. “When we produced this paper, people accused us of ‘painting by numbers,’ or fudging data. But for the first time, you could study vegetation from space based on their photosynthetic capacity.”
When the temperature is right, and water and sunlight are available, plants photosynthesize and produce vegetative material. Leaves strongly absorb blue and red light but reflect near-infrared light back into space. By comparing the ratio of red to near-infrared light, Tucker and his colleagues could quantify the vegetation covering the land. Expanding these observations to the rest of the globe, the scientists could track the impact on plants of rainy and dry seasons elsewhere in Africa, see the springtime blooms in North America, and the after-effects of wildfires in forests worldwide.
Satellites that can monitor the subtle changes in color of the ocean have helped scientists track changes in phytoplankton populations across the globe. The first view of ocean color came from the Coastal Zone Color Scanner, a proof-of concept instrument launched in 1979. Continuous observations of ocean color began with the launch of SeaWIFS in late 1997. The satellite was just in time to capture the transition from El Niño to La Niña conditions in 1998 — revealing just how quickly and dramatically phytoplankton respond to changing ocean conditions.
“The entire Eastern Pacific, from the coast of South America all the way to the dateline, transitioned from what was the equivalent of a biological desert to a thriving rainforest. And we watched it happen in real time,” Feldman said. “For me, that was the first demonstration of the power of this kind of observation, to see how the ocean responds to one of the most significant environmental perturbations it could experience, over the course of just a few weeks. It also showed that the ocean and all the life within it is amazingly resilient — if given half a chance.”
With 20 years of satellite data tracking ocean plant life on a global scale, scientists are investigating how habitats and ecosystems are responding to changing environmental conditions. Recent studies of ocean life have shown that a long-term trend of rising sea surface temperatures is causing ocean regions known as “biological deserts” to expand. These regions of low phytoplankton growth occur in the center of large, slow-moving currents called gyres.
“As the surface waters warm, it creates a stronger boundary between the deep, cold, nutrient-rich waters and the sunlit, generally nutrient-poor surface waters,” Feldman said. This prevents nutrients from reaching phytoplankton at the surface, and could have significant consequences for fisheries and the marine ecosystem.
In the Arctic Ocean, an explosion of phytoplankton indicates change. As seasonal sea ice melts, warming waters and more sunlight will trigger a sudden, massive phytoplankton bloom that feeds birds, sea lions and newly hatched fish. But with warming atmospheric temperatures, that bloom is now happening several weeks early — before the animals are in place to take advantage of it. “It’s not just the amount of food, it’s the location and timing that are just as critical,” Feldman said. “Spring bloom is coming earlier, and that’s going to impact the ecosystem in ways we don’t yet understand.”
The climate is warming fastest in Arctic regions, and the impacts on land are visible from space as well. The tundra of Western Alaska, Quebec and elsewhere is turning greener as shrubs extend their reach northwards. The neighboring northern forests are changing as well. Massive fires in 2004 and 2015 wiped out millions of acres of forests in Alaska, including spruce forests, noted Chris Potter, a research scientist at NASA’s Ames Research Center in California’s Silicon Valley.
“These fires were amazing in the amount of forest area they burned and how hot they burned,” Potter said. “When the air temperature hits 90 degrees Fahrenheit in late May up there, and all these lightning strikes occurred, the forest burned very extensively — close to rivers, close to villages — and nothing could stop it.”
But land is only part of the story. At the base of the ocean’s food web are phytoplankton — tiny organisms that, like land plants, turn water and carbon dioxide into sugar and oxygen, aided by the right combination of nutrients and sunlight.
19/11/2017 5:03 PM
NNNN[related_post themes="text" id="324587"]