A new NASA tool links changes in sea level in 293 global port cities to specific regions of melting land ice, such as southern Greenland and the Antarctic Peninsula. It is intended to help coastal planners prepare for rising seas in the decades to come.
All coastal cities will see some impacts of global sea level rise. But the new tool shows that, for example, New York City is more strongly affected by melting ice in northeastern Greenland than in southwestern Greenland; while Sydney has a greater risk from the rapidly melting Antarctic Peninsula than from East Antarctica.
A paper describing the new tool, titled "Should coastal planners have concern over where land ice is melting?," was recently published in the journal Science Advances. The research team is Eric Larour, Erik Ivins and Surendra Adhikari of NASA's Jet Propulsion Laboratory in Pasadena, California.
Melting ice and rising ocean temperatures contribute about evenly to global sea level rise today. Individual cities are also affected by local conditions such as land sinking. Other Web-based resources such as the U.S. Climate Resilience Toolkit address some of these issues, but the new NASA tool is the only resource to match specific melting ice locations with their effects on the world's ports.
Water from melted ice on land doesn't spread evenly across the world's oceans because of a gravitational push-pull between ice and ocean. As a melting glacier or ice sheet dwindles, it loses mass, causing its local gravitational pull on nearby ocean water to diminish. Seawater that had been pulled toward the ice by the force of gravity flows away — in other words, sea level drops in the vicinity of a melting glacier but rises farther away. When this spatial pattern can be attributed to a given glacier or ice sheet, it is known as a sea level fingerprint.
To calculate this and other influences on sea level such as Earth's rotation, Larour and his colleagues used a dynamic mathematical formula called the adjoint method, which is used in seismic and meteorological studies. The method enables fast computation of the sensitivity of a model's output to its inputs — in this case, the sensitivity of sea level to ice melting. They used the method with JPL's well-tested computer model of ice sheet melting, the Ice Sheet System Model, to develop their new tool, called Gradient Fingerprint Mapping.
Users of the tool need no specialized training or extreme computer power; they simply download it, input data or projections of ice loss, and let it evolve the shifting ice and water patterns forward into the future. The result: a detailed profile of the sensitivity of sea level at any of these cities to changes in ice anywhere in the world.
Calculations of sea level fingerprints have been made in previous studies but tended to be cumbersome and spatially coarse, Larour said. The new tool provides an overall mechanism for rapidly computing high-resolution results using a variety of potential data sets.
Gradient Fingerprint Mapping is not dependent on a particular climate change scenario, Larour said. "You can apply the method to any type of melting scenario that you want." That means it will retain its utility as improved projections of ice loss become available in the future.
The computations show that the specific location of mass loss in Greenland is crucial, as it greatly affects the local sea level predictions for many major coastal cities in North America and Europe. The spatial details of Antarctic melting are important for areas south of the equator in South America, Africa and South Asia.
Among some intriguing results, Larour said, are those for New York, London and Oslo. Greenland’s northeastern ice stream was shown to have an outsized effect on New York’s local sea level, but the island's southern glaciers had little influence. London was more strongly affected by Greenland’s northwestern and western glaciers. And Norway is so close to Greenland, the island's gravitational fingerprint is contributing to sea level decrease in Oslo.
The authors note that ocean dynamics can accelerate or offset the changes in sea level from gravitational fingerprints — particularly in New York, where the contribution of melting ice to accelerated sea level rise is minor compared to other sources.
“This is really a new capability,” Larour said. “Now a coastal planner can understand and see how the melting or growing of a given ice sheet could be detrimental or beneficial to a specific location.”
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Jet Propulsion Laboratory, Pasadena, California
We live on a solar-powered planet. As we wake up in the morning, the Sun peeks over the horizon to shed light on us, blanket us with warmth and provide cues to start our day. At the same time, our Sun’s energy drives our planet’s ocean currents, seasons, weather and climate. Without the Sun, life on Earth would not exist.
For nearly 40 years, NASA has been measuring how much sunshine powers our home planet. This December, NASA is launching an instrument to the International Space Station to continue monitoring the Sun’s energy input to the Earth system. The Total and Spectral solar Irradiance Sensor (TSIS-1) will precisely measure what scientists call “total solar irradiance.” These data will give us a better understanding of Earth’s primary energy supply and help improve models simulating Earth’s climate.
“You can look at the Earth and Sun connection as a simple energy balance. If you have more energy absorbed by the Earth than leaving it, its temperature increases and vice versa,” said Peter Pilewskie, TSIS-1 lead scientist at the Laboratory for Atmospheric Physics (LASP) in Boulder, Colorado. Under NASA’s direction, LASP is providing and distributing the instrument’s measurements to the scientific community. “We’re measuring all the radiant energy that is coming to Earth.”
But it’s not so simple: the Sun’s output energy is not constant. Over the course of about 11 years, our Sun cycles from a relatively quiet state to a peak in intense solar activity — like explosions of light and solar material — called a solar maximum. In subsequent years the Sun returns to a quiet state and the cycle starts over again. The Sun has fewer sunspots — dark areas that are often the source of increased solar activity — and stops producing so many explosions, going through a period called the solar minimum. Over the course of one solar cycle (one 11-year period), the Sun’s emitted energy varies on average at about 0.1 percent. That may not sound like a lot, but the Sun emits a large amount of energy – 1,361 watts per square meter. Even fluctuations at just a tenth of a percent can affect Earth.
In addition to those 11-year changes, entire solar cycles can vary from decade to decade. Scientists have observed unusually quiet magnetic activity from the Sun for the past two decades with previous satellites. During the last prolonged solar minimum in 2008-2009, our Sun was as quiet it has been observed since 1978. Scientists expect the Sun to enter a solar minimum within the next three years, and TSIS-1 will be primed to take measurements of the next minimum.
“We don’t know what the next solar cycle is going to bring, but we’ve had a couple of solar cycles that have been weaker than we’ve had in quite a while so who knows. It’s a pretty exciting time to be studying the Sun,” said Dong Wu, the TSIS-1 project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Goddard is responsible for the overall development and operation of TSIS-1 on the International Space Station.
TSIS-1 data are particularly important for helping scientists understand the causes of total solar irradiance fluctuations and how they are connected with the Sun’s behavior over decades or centuries. Today, scientists have neither enough data nor the forecasting skill to predict whether total solar irradiance has any long-term trend, said Doug Rabin, deputy project scientist at Goddard. TSIS-1 will continue a data sequence that is vital to answering that question.
These data are also important for understanding Earth's climate through models. Scientists use computer models to interpret changes in the Sun’s energy input. If less solar energy is available, scientists can gauge how that will affect Earth’s atmosphere, oceans, weather and seasons by using computer simulations. The input from the Sun is just one of many factors scientists used to model Earth’s climate. Earth’s climate is also affected by other factors such as greenhouse gases, clouds scattering light and small particles in the atmosphere called aerosols — all of which are taken into account in comprehensive climate models.
TSIS-1 will study the total amount of solar radiation emitted by the Sun using the Total Irradiance Monitor, one of two sensors on the instrument. The second sensor, called the Spectral Irradiance Monitor, will measure how the Sun’s energy is distributed over the ultraviolet, visible and infrared regions of light. TSIS-1 spectral irradiance measurements of the Sun's ultraviolet radiation are critical to understanding the ozone layer — Earth's natural sunscreen that protects life from harmful radiation.
“Knowing the Sun’s behavior and knowing how Earth’s atmosphere responds to the Sun is even more important now because of all the different factors that affect climate change. We need to understand how all of these interact on Earth’s system,” said Pilewskie.
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