In late August, as Hurricane Harvey began smashing into the Texas coast, a flood of data began pouring in along with the catastrophic quantities of rainwater.
It wasn’t from the nonstop news coverage; it was from the transmissions that lay behind it, in the pulses of information coming down from space.
The US National Oceanic and Atmospheric Administration’s (NOAA) geostationary and polar-orbiting satellites, crucial tools for monitoring big storms in the Gulf of Mexico, were capturing cloud formations, surface temperatures, and barometric pressures, which were then fed into computer models tracking the storm’s strength and intensity.
At the same time, Nasa (the National Aeronautics and Space Administration) was using a group of satellites to keep tabs on soil moisture, flood patterns, and power failures all over East Texas.
In various ways, this torrent of data was being collected continuously from hundreds (or even thousands) of kilometres overhead, through radar instruments and spectroradiometer sensors and exquisitely-calibrated imaging cameras.
The machines being used aren’t household names, but they demonstrate why the popular view of Earth as a big blue planet with only the Moon as its companion could do with some revising.
We are also surrounded by a constellation of satellites spinning elliptical webs of environmental observation, day and night.
The array of American satellites, comprising dozens of NOAA and Nasa missions, is the product of some 40 years of experimentation and investment on the part of the federal government.
They’re joined in their orbit by weather and climate satellites from scientific agencies in Europe and Asia, along with a host of satellite-borne sensors from both the private sector and the military, that measure everything from air pollution to land development to agriculture.
Without question, we’re living at the start of a dark era of warming climates.
But we’re also living in a golden age of environmental data, in which our technology in space can deliver surprising measurements with profound implications.
After a big hurricane such as Irma or Harvey dumps extraordinary amounts of water on a region, for instance, a pair of satellites known as the Gravity Recovery And Climate Experiment (Grace) is able to assess how much water floods in and how it dissipates as the storm recedes.
A joint mission of Nasa and the German Aerospace Center, Grace’s two spacecraft have been circling Earth every 90 minutes for the past 15 years at an altitude of 480km or so.
On a dark, clear night, you can sometimes see them for a brief moment: Two bright, blurry dots, rushing by at a velocity of about 27,600kph.
By monitoring how their positions in space are affected by gravity, scientists can draw a number of conclusions about what’s happening on Earth, especially to our freshwater resources.
Yet Grace also illustrates how tenuous the golden age of data really is. The two craft, which were launched in 2002, were originally expected to orbit the planet for five years.
They are now dying, and in fact the batteries on one of the satellites are so depleted that it periodically goes to sleep. Since 2010, Nasa has been planning and building replacements, and if all goes well, they will be in orbit early next year.
But if Grace goes dark or perishes before then, there will be a break in Nasa’s continuous observation of Earth’s gravity field and water dynamics.
Climate researchers will be confronted with what’s known as a data gap, which can leave them at a loss for drawing scientific conclusions about environmental trends.
This sort of gap has threatened to become a more common problem in recent months. The US federal government’s entire climate-science enterprise, much of it linked to Nasa’s satellite research, is under duress.
The White House asked that Nasa drop four climate-related missions in its Earth-sciences division, which accounts for about 10% of Nasa’s $19bn (€16bn) annual budget.
It also unveiled a plan to cut 18% from NOAA’s annual spending on satellites, which would force a huge reduction in the agency’s climate work.
Even if the science agencies avoid the worst, however, the Trump administration’s intention to slash funding on technology that helps make planetary surveys possible — much of it obscure to the public — signals an embattled future for this type of research.
The effects are hard to predict. Most of the US’s climatic and meteorological information shares a common origin, even when it seems to come from the Weather Channel or CNN.
“The monitoring of the atmosphere, of the surface of the Earth, of what’s going on in the ocean and under the ice — all of that is overwhelmingly funded by the federal government,” John Holdren, former president Barack Obama’s chief science adviser and a Harvard professor of environmental science and policy, told me recently.
Every satellite has its own story, and Grace’s begins in the summer of 1969 at a Nasa-sponsored conference in Williamstown, Massachusetts.
The scientists convened there to discuss how a variety of new technological tools and sensors might allow them to gain a better understanding of our planet.
Several recommendations emerged from the gathering, among them the suggestion that the agency launch satellites to measure sea levels, monitor changes in Earth’s crust and analyse the planet’s gravity.
The reason for wanting precise gravity measurements was practical as well as scientific. The gravitational pull on an object can be greater where Earth’s mass is denser — above mountain ranges such as the Rockies or Alps, say, or over vast ice sheets like Antarctica’s.
The resulting variations in gravity have subtle but important effects on the paths of ballistic missiles, for example, which the US Department of Defense cares deeply about.
By the time of the Williamstown conference, satellite observations of Earth, which were beginning to be referred to as “remote sensing,” seemed enormously promising.
In the 1960s, Nasa and other government agencies started launching Earth-orbiting satellites to study weather patterns, ocean circulation and agriculture.
By the late 1970s, some of them, with names such as Landsat and Seasat, carried sophisticated microwave and laser instruments and imaging equipment.
A few of these satellites fulfilled the recommendations laid out at illiamstown. Subsequent missions took their cue from an expanded vision for Earth observations put forward by Nasa administrators in the 1980s.
One of their reports presciently urged that scientists focus on how human activity was warming the planet, noting that “the burning of oil and coal is injecting carbon dioxide into the atmosphere at unprecedented and accelerating rates”.
Eventually, the Nasa directives of the 1980s led to a number of satellites that were deployed in the 1990s and early 2000s, like Aqua, Terra, Aura, and IceSat.
Some of these missions are still orbiting and considered vital to Earth observations. Byron Tapley, the director of the Center for Space Research at the University of Texas at Austin, told me that during this era he worked on various Nasa satellite efforts that would have measured Earth’s gravity field, but none of them made it to launch.
That changed with the proposal for Grace, which was written in large part by Dr Tapley’s former student from Austin, Mike Watkins, who had gone to work at Nasa’s Jet Propulsion Laboratory (JPL). Nasa gave the go-ahead in 1997.
The goal for Grace was to produce an unprecedentedly accurate reading of Earth’s gravity field. But, early on, Dr Watkins began to think that its two craft could also register details on what’s known as variable gravity, which mostly depends on the way water moves around the world under the influence of seasonal changes, droughts and other climate factors. Where there’s more water in one place, there’s more gravitational pull.
A good illustration of the satellite’s promise had to do with the problem of measuring variation in the world’s great ice caps.
When the first Grace satellite approached, say, the Greenland ice sheet, which weighs about three quadrillion tons, the craft would presumably respond to the subtle gravitational tug and be pulled slightly forward and away from its trailing partner.
The distance between them — 200km or so — might increase by less than a human hair. But because the twin spacecraft were in constant contact with each other through a microwave communication link, that change could still be measured precisely.
And it could be measured over and over again, month after month, year after year. In the mid-1990s, Dr Watkins and his colleagues started to do detailed simulations.
“We wondered: How much can we measure changes in the Greenland and Antarctic ice sheets? How well can we measure aquifer changes in groundwater? And we started to realise that this was the thing that was really going to break the mission wide open.”
The proposal he wrote expressed confidence that they could get a measurement for the planet’s gravity field, but as Dr Watkins recalled, it also hinted: “Here’s this other supercool thing we can do.”
Grace was authorised during an era at Nasa, the late 1990s, when some science missions were approved on the condition that they satisfy an agency directive to be “faster, better, cheaper”.
The joke at Nasa at the time was that you get only two out of the three. What ultimately made Grace possible was a cost-sharing partnership between American scientists and the German Research Centre for Geosciences, GFZ, and the German Aerospace Center (DLR).
By the time of the launch, the cost amounted to $97m for Nasa and about $30m for Germany.
One lesson of publicly funded science is that Americans are not very good at predicting how useful it will be. It’s only later that we look back and see how the investments paid off.
Some of the returns are economic; most of the crucial components of smartphones (not to mention the internet itself) began with publicly-funded science, for instance. Investments in the collection of climate data fall into a similar category: They started as science projects, then gave us significant economic and social information — such as insights into hurricanes and droughts.
The ‘E’ in Grace may stand for “experiment”, but the project produced useful data fairly quickly. Measuring the Greenland and Antarctic ice sheets was a case in point.
In the 1990s, researchers tried various methods on the ground to record the height of the Greenland ice sheet from year to year to determine its loss or gain.
But Grace promised a different, and previously impossible, kind of calculation.
In 2006, Isabella Velicogna (inset) and John Wahr, both at the University of Colorado at Boulder, published two studies that interpreted the first few years of Grace data; their initial paper was about Antarctica’s loss of ice, while the second was about Greenland’s, which appeared to be losing at least 100bn tons per year.
Some scientists were awestruck. Dr Velicogna, now a professor at the University of California at Irvine and a JPL scientist, told me the Grace measurements didn’t suddenly make field studies of individual glaciers less important — the data couldn’t tell scientists why the ice sheet was losing mass.
But they let her systematically account for drastic losses in places so far-flung that they were almost impossible for human beings to reach, such as parts of Greenland and West Antarctica.
What’s more, the measurements enabled glaciologists to look at the decline of massive mountain glaciers, like those in Central Asia, which are a critical resource for regional water supplies.
As Dr Velicogna noted, those glaciers “could mean the difference between life and death in those places”. They can also lead to profound geopolitical conflicts. Grace soon indicated that many were shrinking.
Similar changes began to be revealed in the world’s hidden aquifers. Jay Famiglietti, a hydrologist at JPL who focuses on tracking changes in groundwater — water stored in underground aquifers around the world — worked as a professor at the University of Texas at Austin in the late 1990s.
As the data began coming in, Dr Famiglietti found that Grace could measure groundwater with astounding effectiveness. He came up with a nickname for Grace — “the scale in the sky” — and began tracking California’s water supplies during what eventually became a decade of unrelenting drought.
One of Grace’s shortcomings is its limited resolution: It can map increases and losses in only large aquifers. Still, Dr Famiglietti told me that, from 2011 to 2015, California lost so much water every year — trillions of litres — that it showed up clearly in the Grace measurements.
About two-thirds of the losses appeared to be groundwater. He also noted that the satellites were able to capture a freshwater predicament bigger than California’s.
Before Grace, Dr Famiglietti said, most of our knowledge about underground water reserves was a hodgepodge.
“What Grace added was a regional, global understanding — like, holy crap, this is happening all over the world,” he said.
In 2015, Dr Famiglietti’s team used Grace to determine that more than half of the world’s largest aquifers were “past sustainability tipping points”. And beyond showing declines in the world’s ice sheets and aquifers, Grace clarified the factors influencing the rise in sea levels.
The goal of remote sensing is not merely to measure unmeasured aspects of the planet. It’s to measure them nonstop, ideally for decades on end, so that long-term trends can be identified in a notoriously chaotic and variable natural world.
The US administration’s exit from the Paris accords this year represents a public retreat from diplomatic engagement on climate change.
But its budget priorities — seeking to minimize the need, as well as the means, for gathering climate information — suggest the start of a quieter but arguably more consequential shift: undercutting the very data and evidence that has helped bring urgency to the issue.
While there have always been policy debates about allocating taxpayer money to environmental research, according to Dr Holdren, the fundamental reason we collect the data is because it has long been considered an apolitical “public good”, with a variety of benefits for the nation’s economy, public health and safety.
For almost a decade, the fear has been that Grace will die before a replacement mission could sustain its data stream.
Dr Tapley, the lead investigator, recalled that, in 2010, his team settled on replicating Grace precisely rather than building a more sophisticated and expensive improvement.
“We decided we want to get the follow-on as quick as we can,” he told me. “We don’t want to break the timeline. We’ll use a cookie-cutter approach.
And let’s see if we can get the Germans to partner with us again.”
In fact, the proposed model wasn’t called Grace-2 — that was the souped-up version — but Grace-FO, for Grace Follow-On.
This time, though, the process would not be “better, faster cheaper” — not when it would require about $450m (€381m) from Nasa and $100m from Germany.
I went to see the replacement satellites at an aerospace facility on the outskirts of Munich. The Grace-FO twins — each about three metres long and a metre high — were positioned next to each other under bright lights in a sealed white room.
Supporting racks held each spacecraft at shoulder height; each had its side panels open, exposing metallic innards. The engineers hovering around gave the place the feel of a surgical theatre.
Frank Webb, Grace-FO’s project scientist, who works out of the JPL happened to be there. We were joined by Peter Gath, the project manager for the German team. Everyone wore long white coats and covers over shoes and hair. As we entered the clean room, he warned me: “Don’t touch anything.”
At the time of my visit, the satellites were essentially finished. If all went according to plan, before the end of the year they would return to California and be installed within a SpaceX Falcon 9 rocket that would take off from Vandenberg Air Force Base, northwest of Los Angeles. The launch date, Webb said, would most likely be in early 2018.
Before we left the room in Munich, Dr Gath also let me know that while the satellites had been built separately, “they will stay together from now on”.
I found this reassuring. It was as though the two spacecraft were the kind of close companions that would need each other’s support to endure a difficult set of circumstances, which in a sense they will.
Whatever the larger fate of our climate research, if you assume a safe deployment for Grace-FO, the twins might circle Earth together for 3bn kilometres or so, measuring the subtle gravitational tug of our water much as their predecessors have, until their orbits drop and drop and then drop so much that both burn up and vanish.
And at that far-off point — assuming that there is still the will to spend the money and keep taking the measure of the planet — the whole process would begin again.