However, throughout the United States, the elevations of various structures, natural features, and landscapes are expected to change in relation to average sea level. This shift will result in most areas becoming shorter, with regions in the Pacific Northwest predicted to decrease by up to 5 feet and parts of Alaska by 6 1/2 feet, according to Juliana P Blackwell, director of the National Geodetic Survey. Seattle, for example, is projected to be 4.3 feet lower than its current elevation. This adjustment is due to the fact that height is relative to a reference point, and geodesists are revising the reference point, or vertical datum, from which height measurements are determined while calculating the Earth's shape, size, gravitational field, and orientation in space over time. It is a highly challenging task in mathematics and physics that has taken fifteen years to complete. Chris Rizos, president-elect of the International Union of Geodesy and Geophysics and an emeritus professor at the University of New South Wales, describes the project as significant for the US. The project, known as "height modernization," is part of a larger initiative by the National Oceanic and Atmospheric Administration to accurately determine the US's location on Earth. The new National Spatial Reference System, including height, latitude, longitude, and time, is expected to be implemented in late 2022 or 2023. This system will replace outdated reference systems from the 1980s that were based on outdated calculations. The mistakes in elevation become larger as you travel diagonally from the southeast to the northwest in the country. The only region in the US where the elevation is predicted to remain the same or increase slightly is the southern tip of Florida. Blackwell noted that there is a noticeable tilt where all the errors in the vertical network are shifted towards the northwest. Height has always been linked to pride and some people in Colorado are concerned that a few of their mountain peaks may not meet the minimum elevation required for bragging rights under the new system, according to Blackwell. “They are very proud of how high these things are, and I know that it’s going to be a bit of a bummer if they start to be a little bit shorter than they were thought to be previously,” she said. She added that she is not yet sure precisely what the new measurements of Colorado’s peaks will be. And near Beaumont, Texas, citizens are grappling with the unwelcome news that certain areas have subsided so much since previous height calculations that these regions now sit in the floodplain. As a result, some landowners may now need to insure themselves against losses from floods, said Daniel R Roman, chief geodesist at NOAA. “They didn’t want to know that the heights had changed,” he said, “because when they do floodplain mapping, they’re like, ‘Well, I’m this height — it hasn’t changed.’” The US has been measuring its height since 1807, when Thomas Jefferson, then the president, established the Survey of the Coast, forerunner to the National Geodetic Survey, to chart the waters and coasts on the Eastern Seaboard. The survey was the first civilian scientific organization in the country with the goal of improving shipping safety. As the nation expanded towards the west, so did the process of measuring, with the coast serving as a reference point for sea level. Surveyors placed metal bench marks in the land as they journeyed, noting the height above sea level at each point, often on a mile by mile basis. Those interested in measuring the height of a building or hill would do so in relation to the bench mark and, ultimately, to sea level. Geodetic levelling, which was known for being meticulous and costly, aimed to ensure that heights were consistently measured nationwide over time, rather than each region having its own method. For instance, if engineers from different states were constructing a bridge spanning state borders, they needed to be confident it would align perfectly in the center. By 1900, geodesy had advanced, with experts no longer relying on a coastline as a substitute for sea level, but instead creating a model of sea level based on tidal data. They have made adjustments to the height reference five times since then, in the years 1903, 1907, 1912, 1929, and 1988. The 1988 model is currently the standard in the US and Mexico. However, the 1988 version did not provide accurate information for California and parts of Texas and North Carolina due to significant movements in the crust caused by tectonic plate activity and extraction of oil, gas, and water from underground. To address this issue, David B Zilkoski, a former director of the National Geodetic Survey and geodesist, suggested using global navigational satellite system technologies like GPS, which were becoming more widely available at the time. GPS is very accurate in determining your location in a two-dimensional space, such as at a specific intersection. However, it can also provide your location in a three-dimensional world, including your height above sea level. By the mid-1990s, the idea of using GPS to update height measurements became popular due to its cost-effectiveness and simplicity. Satellites and GPS systems calculate height based on a smoothed-out mathematical model of the Earth's shape known as an ellipsoid. Imagine a basketball that is flattened at the top and bottom. However, there was a significant issue. According to James L Davis, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory in New York, GPS technology has limitations when it comes to understanding gravity. This topographic research is being conducted in the Glacier Bay region of Alaska. Geodesists are concerned with gravity because height is determined by the direction and strength of gravity, which is influenced by the density of the material below and near the terrain. This means that height is not just a measurement of distance above the ground, but is closely connected to gravity. Geodesists prefer to use the term "height" instead of "elevation" because gravity is linked to the distribution of mass. According to Davis, when giving public lectures on gravity, a significant portion of the talk is dedicated to changing people's perspective on the topic. Therefore, relying solely on GPS for measuring height can lead to inaccuracies, as variations in gravity must also be considered. The National Geodetic Survey initiated the GRAV-D mission in 2007 to incorporate detailed gravitational field measurements into GPS height calculations to create a more accurate model of average sea level worldwide, including on land. Due to the varying pull of gravity across different locations, a model known as the geoid is used, which has a lumpy potato-like shape. All height measurements will now consider this model. Once the new height system is implemented, it is expected that people will discover unexpected applications for it, according to Blackwell from the National Geodetic Survey. She referenced "The Jetsons," a futuristic animated show from the 1960s where characters traveled around their cities in small spacecraft. The technology that allows for quick and accurate calculations of heights and other positional coordinates was previously unimaginable. Today, the importance of precise three-dimensional navigation is increasing with the widespread use of drones, self-driving cars, and remote aerial systems. Despite improvements in calculating the Earth's shape by geodesists, human activities such as global warming are altering the planet. As glaciers and ice sheets melt, their mass is transferred from land to ocean, leading to rising sea levels and ultimately affecting elevation measurements based on sea level. The change in mass also impacts the planet's structure, according to Davis from Columbia University. The mass on Earth's surface causes it to deform, due to the pressure applied. Essentially, human activity, particularly through the alteration of the atmosphere, is changing gravity globally. Davis explained that this is happening as chemical changes in the atmosphere lead to the redistribution of mass, resulting in a significant increase in overall mass. Davis and other researchers are working to improve their calculations of the impact of human activity on the Earth, particularly in terms of changes in the geoid shape and rotation. The focus has shifted from understanding the Earth's shape to predicting future changes, such as glacier mass loss. The urgency of the situation is evident as scientists strive to accurately predict what will happen in the coming years.