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Until relatively recently, humans were limited by the horizon. Climate scientists of the early 20th century could gather data from the world around them and perhaps what they were able to see from a hot air balloon or plane. But the really big picture – the global snapshot – remained out of sight.
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The first satellite of any kind was the USSR’s Sputnik 1, launched in 1957. But it wasn’t until the 1960s that satellites designed specifically to observe the Earth and its climate made it into orbit and gave us the first overview of weather patterns. By the 1970s Nasa’s Landsat satellites were able to monitor things like tree cover.
Jonathan Bamber, a climate scientist at the University of Bristol, says this “revolutionised our ability to carry out a comprehensive and timely health check on the planetary systems we rely on for our survival”. Data that once required months or even years of fieldwork was suddenly available in the time it took a satellite to orbit the planet.
These days, this data can be remarkably precise and detailed. Bamber says: “We can measure changes in sea level down to a single millimetre, changes in how much water is stored in underground rocks, the temperature of the land and ocean and the spread of atmospheric pollutants and greenhouse gases, all from space.”
Here’s a map of sea level rise, from Bamber’s article highlighting five satellite images that show how fast our planet is changing:
“This image,” writes Bamber, “shows mean sea level trends over 13 years in which the global average rise was about 3.2mm a year. But the rate was three or four times faster in some places, like the south western Pacific to the east of Indonesia and New Zealand, where there are numerous small islands and atolls that are already very vulnerable to sea level rise.”
Read more: Five satellite images that show how fast our planet is changing
In recent years, scientists have used AI to sift through and analyse satellite data. Bamber’s latest research, published in January this year, illustrates this nicely.
A team of scientists, lead by Tian Li also of the University of Bristol, gathered millions of satellite images of glaciers in Svalbard, a remote and icy archipelago in the Arctic Ocean. In their write up, they note that human researchers once painstakingly looked through this sort of data.
“This process”, they write, “is highly labour-intensive, inefficient and particularly unreproducible as different people can spot different things even in the same satellite image. Given the number of satellite images available nowadays, we may not have the human resources to map every region for every year.”
Their solution was to use AI to “quickly identify glacier patterns across large areas”. The satellite-AI combo meant they could examine Svalbard’s retreating glaciers – surely among the least accessible places on the planet – in “unprecedented scale and scope”.
They found that 91% of the many glaciers that flow into the sea around the archipelago have been “shrinking significantly”. They note that the same types of glacier can be found across the Arctic, and “what happens to glaciers in Svalbard is likely to be repeated elsewhere”.
Many of those glaciers can be found in Greenland, home of the northern hemisphere’s largest ice sheet. In research published earlier this month, Tom Chudley of Durham University used satellite images to assess crevasses (cracks in the glaciers) in Greenland.
Chudley also combined satellite images with computerised analysis. His work made use of “ArcticDEM”, three dimensional maps of the polar regions based on high resolution satellite images.
“By applying image-processing techniques to over 8,000 maps, we could estimate how much water, snow or air would be needed to “fill” each crevasse across the ice sheet. This enabled us to calculate their depth and volume, and examine how they evolved.“
His conclusion was very blunt: the Greenland ice sheet is falling apart.
Read more: The Greenland ice sheet is falling apart – new study
Health watchdogs
Many of you will be well aware that satellites are being used to monitor the health of the planet. What’s less well known is the role they can play in monitoring human health.
Dhritiraj Sengupta, a satellite scientist at Plymouth Marine Laboratory, says satellites have become Earth’s new health and nature watchdog. His article details how satellites can map mosquito breeding sites to combat malaria, for instance, or can identify air pollution hotspots in cities.
In his own research, he’s used satellite-derived chlorophyll data to assess the risk of cholera. Chlorophyll is the green pigment in plants that helps them use sunlight to make their food and grow.
“Many bacteria like Vibrio cholerae which causes cholera, thrive in stagnant water,” Sengupta writes. “My team worked with the European Space Agency to show that its presence can be modelled using the concentration of chlorophyll found on the surface of bodies of water.”
Read more: How satellites have become Earth’s new health and nature watchdogs
So far, so good. Satellites have undeniably been useful for climate scientists. But in the longer-term, the satellites themselves may have an unforeseen effect on the climate.
Last year, SpaceX announced it would “deorbit” 100 of its Starlink satellites to burn up in the atmosphere. Fionagh Thomson is a space expert, also at Durham University. She says that “atmospheric scientists are increasingly concerned that this sort of apparent fly-tipping by the space sector will cause further climate change down on Earth.”
Particles from the satellites themselves won’t have a huge effect compared to the “440 tonnes of meteoroids that enter the atmosphere daily, along with volcanic ash and human-made pollution from industrial processes on Earth.”
But one team “recently, and unexpectedly, found potential ozone-depleting metals from spacecraft in the stratosphere, the atmospheric layer where the ozone layer is formed.” The worry is that satellite debris may help form certain types of clouds that lead to ozone loss and may add to the greenhouse effect.
She notes that this is all uncertain and needs more research. “But,” she writes, “we’ve also learnt that if we wait until indisputable evidence is available, it may be too late, as with the loss of ozone. It’s a constant dilemma.”
Something for SpaceX scientists to look into, perhaps, once they’ve finished rescuing stranded astronauts from the International Space Station.
