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An improved view of global sea ice


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    • By NASA
      5 Min Read Antarctic Sea Ice Near Historic Lows; Arctic Ice Continues Decline
      On Feb. 20, 2024, Antarctic sea ice officially reached its minimum extent for the year. This cycle of growth and melting occurs every year, with the ice reaching its smallest size during the Southern Hemisphere's summer. Credits: NASA's Scientific Visualization Studio/Trent L. Schindler Sea ice at both the top and bottom of the planet continued its decline in 2024. In the waters around Antarctica, ice coverage shrank to near-historic lows for the third year in a row. The recurring loss hints at a long-term shift in conditions in the Southern Ocean, likely resulting from global climate change, according to scientists at NASA and the National Snow and Ice Data Center. Meanwhile, the 46-year trend of shrinking and thinning ice in the Arctic Ocean shows no sign of reversing.
      “Sea ice acts like a buffer between the ocean and the atmosphere,” said ice scientist Linette Boisvert of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Sea ice prevents much of the exchange of heat and moisture from the relatively warm ocean to the atmosphere above it.”
      Less ice coverage allows the ocean to warm the atmosphere over the poles, leading to more ice melting in a vicious cycle of rising temperatures.
      Historically, the area of sea ice surrounding the Antarctic continent has fluctuated dramatically from year to year while averages over decades have been relatively stable. In recent years, though, sea ice cover around Antarctica has plummeted.
      On Feb. 20, 2024, Antarctic sea ice officially reached its minimum extent for the year. This cycle of growth and melting occurs every year, with the ice reaching its smallest size during the Southern Hemisphere’s summer. According to the National Snow and Ice Data Center, this marks the second-lowest sea ice extent recorded by satellites, reflecting a trend of declining coverage over time.
      Credit: NASA’s Goddard Space Flight Center/Scientific Visualization Studio
      Download this video in HD formats from https://svs.gsfc.nasa.gov/14538.
      “In 2016, we saw what some people are calling a regime shift,” said sea ice scientist Walt Meier of the National Snow and Ice Data Center at the University of Colorado, Boulder. “The Antarctic sea ice coverage dropped and has largely remained lower than normal. Over the past seven years, we’ve had three record lows.”
      This year, Antarctic sea ice reached its lowest annual extent on Feb. 20 with a total of 768,000 square miles (1.99 million square kilometers). That’s 30% below the 1981 to 2010 end-of-summer average. The difference in ice cover spans an area about the size of Texas. Sea ice extent is defined as the total area of the ocean in which the ice cover fraction is at least 15%.
      This year’s minimum is tied with February 2022 for the second lowest ice coverage around the Antarctic and close to the 2023 all-time low of 691,000 square miles (1.79 million square kilometers). With the latest ice retreat, this year marks the lowest three-year average for ice coverage observed around the Antarctic continent across more than four decades.
      The changes were observed in data collected with microwave sensors aboard the Nimbus-7 satellite, jointly operated by NASA and the National Oceanic and Atmospheric Administration (NOAA), along with satellites in the Defense Meteorological Satellite Program.
      NASA’s Earth Observatory: Antarctic Sea Ice at Near-Historic Lows Meanwhile, at the other end of the planet, the maximum winter ice coverage in the Arctic Ocean is consistent with an ongoing 46-year decline. Satellite images reveal that the total area of the Arctic Ocean covered in sea ice reached 6 million square miles (15.65 million square kilometers) on March 14. That’s 247,000 square miles (640,000 square kilometers) less ice than the average between 1981 and 2010. Overall, the maximum winter ice coverage in the Arctic has shrunk by an area equivalent to the size of Alaska since 1979.
      This year’s Arctic ice maximum is the 14th lowest on record. Complex weather patterns make it difficult to predict what will happen in any given year.
      The Arctic Ocean sea ice reached its annual maximum on March 14, continuing the long-term decline in ice at the poles.Chart by Lauren Dauphin/NASA Earth Observatory, using data from the National Snow and Ice Data Center. Shrinking ice makes Earth more susceptible to solar heating. “The sea ice and the snow on top of it are very reflective,” Boisvert said. “In the summer, if we have more sea ice, it reflects the Sun’s radiation and helps keep the planet cooler.”
      On the other hand, the exposed ocean is darker and readily absorbs solar radiation, capturing and retaining that energy and ultimately contributing to warming in the planet’s oceans and atmosphere. 
      Sea ice around the poles is more susceptible to the weather than it was a dozen years ago. Ice thickness measurements collected with laser altimeters aboard NASA’s ICESat-2 satellite show that less ice has managed to stick around through the warmer months. This means new ice must form from scratch each year, rather than building on old ice to make thicker layers. Thinner ice, in turn, is more prone to melting than multi-year accumulations.
      “The thought is that in a couple of decades, we’re going to have these essentially ice-free summers,” Boisvert said, with ice coverage reduced below 400,000 square miles (1 million square kilometers) and most of the Arctic Ocean exposed to the Sun’s warming glare.
      It’s too soon to know whether recent sea ice lows at the South Pole point to a long-term change rather than a statistical fluctuation, but Meier believes long term declines are inevitable.
      “It’s only a matter of time,” he said. “After six, seven, eight years, it’s starting to look like maybe it’s happening. It’s just a question of whether there’s enough data to say for sure.”
      Reference: NSIDC Sea Ice Index Daily and Monthly Image Viewer By James Riordon
      NASA’s Earth Science News Team

      Media contact: Elizabeth Vlock
      NASA Headquarters
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      Last Updated Mar 25, 2024 EditorGoddard Digital TeamLocationGoddard Space Flight Center Related Terms
      Earth Climate Change Goddard Space Flight Center Ice & Glaciers Sea Ice Explore More
      5 min read Arctic Sea Ice 6th Lowest on Record; Antarctic Sees Record Low Growth
      Arctic sea ice likely reached its annual minimum extent on September 19, 2023, making it…
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    • By European Space Agency
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    • By NASA
      Sea level rise is affecting coastal communities around the world, especially those like Honolulu, pictured, that are located on islands.NOAA Teacher at Sea Program, NOAA Ship HI’IALAKAI A long-term sea level dataset shows ocean surface heights continuing to rise at faster and faster rates over decades of observations.
      Global average sea level rose by about 0.3 inches (0.76 centimeters) from 2022 to 2023, a relatively large jump due mostly to a warming climate and the development of a strong El Niño. The total rise is equivalent to draining a quarter of Lake Superior into the ocean over the course of a year.
      This NASA-led analysis is based on a sea level dataset featuring more than 30 years of satellite observations, starting with the U.S.-French TOPEX/Poseidon mission, which launched in 1992. The Sentinel-6 Michael Freilich mission, which launched in November 2020, is the latest in the series of satellites that have contributed to this sea level record.
      The data shows that global average sea level has risen a total of about 4 inches (9.4 centimeters) since 1993. The rate of this increase has also accelerated, more than doubling from 0.07 inches (0.18 centimeters) per year in 1993 to the current rate of 0.17 inches (0.42 centimeters) per year.
      This graph shows global mean sea level (in blue) since 1993 as measured by a series of five satellites. The solid red line indicates the trajectory of this increase, which more than doubled over the past three decades. The dotted red line projects future sea level rise.NASA/JPL-Caltech “Current rates of acceleration mean that we are on track to add another 20 centimeters of global mean sea level by 2050, doubling the amount of change in the next three decades compared to the previous 100 years and increasing the frequency and impacts of floods across the world,” said Nadya Vinogradova Shiffer, director for the NASA sea level change team and the ocean physics program in Washington.
      Seasonal Effects
      Global sea level saw a significant jump from 2022 to 2023 due mainly to a switch between La Niña and El Niño conditions. A mild La Niña from 2021 to 2022 resulted in a lower-than-expected rise in sea level that year. A strong El Niño developed in 2023, helping to boost the average amount of rise in sea surface height.
      La Niña is characterized by cooler-than-normal ocean temperatures in the equatorial Pacific Ocean. El Niño involves warmer-than-average ocean temperatures in the equatorial Pacific. Both periodic climate phenomena affect patterns of rainfall and snowfall as well as sea levels around the world.
      “During La Niña, rain that normally falls in the ocean falls on the land instead, temporarily taking water out of the ocean and lowering sea levels,” said Josh Willis, a sea level researcher at NASA’s Jet Propulsion Laboratory in Southern California. “In El Niño years, a lot of the rain that normally falls on land ends up in the ocean, which raises sea levels temporarily.”
      To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video
      This animation shows the rise in global mean sea level from 1993 to 2023 based on data from a series of five international satellites. The spike in sea level from 2022 to 2023 is mostly a consequence of climate change and the development of El Niño conditions in the Pacific Ocean. Credit: NASA’s Scientific Visualization Studio A Human Footprint
      Seasonal or periodic climate phenomena can affect global average sea level from year to year. But the underlying trend for more than three decades has been increasing ocean heights as a direct response to global warming due to the excessive heat trapped by greenhouse gases in Earth’s atmosphere.
      “Long-term datasets like this 30-year satellite record allow us to differentiate between short-term effects on sea level, like El Niño, and trends that let us know where sea level is heading,” said Ben Hamlington, lead for NASA’s sea level change team at JPL.
      These multidecadal observations wouldn’t be possible without ongoing international cooperation, as well as scientific and technical innovations by NASA and other space agencies. Specifically, radar altimeters have helped produce ever-more precise measurements of sea level around the world. To calculate ocean height, these instruments bounce microwave signals off the sea surface, recording the time the signal takes to travel from a satellite to Earth and back, as well as the strength of the return signal.
      The researchers also periodically cross-check those sea level measurements against data from other sources. These include tide gauges, as well as satellite measurements of factors like atmospheric water vapor and Earth’s gravity field that can affect the accuracy of sea level measurements. Using that information, the researchers recalibrated the 30-year dataset, resulting in updates to sea levels in some previous years. That includes a sea level rise increase of 0.08 inches (0.21 centimeters) from 2021 to 2022.
      When researchers combine space-based altimetry data of the oceans with more than a century of observations from surface-based sources, such as tide gauges, the information dramatically improves our understanding of how sea surface height is changing on a global scale. When these sea level measurements are combined with other information, including ocean temperature, ice loss, and land motion, scientists can decipher why and how seas are rising.
      Learn more about sea level and climate change:
      https://sealevel.nasa.gov/
      News Media Contacts
      Jane J. Lee / Andrew Wang
      Jet Propulsion Laboratory, Pasadena, Calif.
      818-354-0307 / 626-379-6874
      jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov
      2024-031
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      Last Updated Mar 21, 2024 Related Terms
      Oceans Climate Change Earth Jet Propulsion Laboratory Sentinel-6 Michael Freilich Satellite TOPEX / Poseidon (ocean TOPography EXperiment) Explore More
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    • By NASA
      4 min read
      NASA Radar Finds Ice Deposits at Moon’s North Pole
      Additional evidence of water activity on moon
      Using data from a NASA radar that flew aboard India’s Chandrayaan-1 spacecraft, scientists have detected ice deposits near the moon’s north pole. NASA’s Mini-SAR instrument, a lightweight, synthetic aperture radar, found more than 40 small craters with water ice. The craters range in size from 1 to 9 miles (2 to15 km) in diameter. Although the total amount of ice depends on its thickness in each crater, it’s estimated there could be at least 1.3 trillion pounds (600 million metric tons) of water ice.
      Mini-SAR map of the Circular Polarization Ratio (CPR) of the north pole of the Moon. Fresh, “normal” craters (red circles) show high values of CPR inside and outside their rims. This is consistent with the distribution of rocks and ejected blocks around fresh impact features, indicating that the high CPR here is surface scattering. The “anomalous” craters (green circles) have high CPR within, but not outside their rims. Their interiors are also in permanent sun shadow. These relations are consistent with the high CPR in this case being caused by water ice, which is only stable in the polar dark cold traps. We estimate over 600 million cubic meters (1 cubic meter = 1 metric ton) of water in these features. The Mini-SAR has imaged many of the permanently shadowed regions that exist at both poles of the Moons. These dark areas are extremely cold and it has been hypothesized that volatile material, including water ice, could be present in quantity here.  The main science object of the Mini-SAR experiment is to map and characterize any deposits that exist.   
      Mini-SAR is a lightweight (less than 10 kg) imaging radar.  It uses the polarization properties of reflected radio waves to characterize surface properties.  Mini-SAR sends pulses of radar that are left-circular polarized.  Typical planetary surfaces reverse the polarization during the reflection of radio waves, so that normal echoes from Mini-SAR are right circular polarized.  The ratio of received power in the same sense transmitted (left circular) to the opposite sense (right circular) is called the circular polarization ratio (CPR).  Most of the Moon has low CPR, meaning that the reversal of polarization is the norm, but some targets have high CPR.  These include very rough, fresh surfaces (such as a young, fresh crater) and ice, which is transparent to radio energy and multiply scatters the pulses, leading to an enhancement in same sense reflections and hence, high CPR.  CPR is not uniquely diagnostic of either roughness or ice; the science team must take into account the environment of the occurrences of high CPR signal to interpret its cause.

      The fresh impact crater Main L (14 km diameter, 81.4° N, 22° E ), which shows high CPR inside and outside its rim. SC is the “same sense, circular” polarization; CPR is “circular polarization ratio.” The histograms at right show that the high CPR values within (red line) and outside the crater rim (green line) are nearly identical. Numerous craters near the poles of the Moon have interiors that are in permanent sun shadow.  These areas are very cold and water ice is stable there essentially indefinitely.  Fresh craters show high degrees of surface roughness (high CPR) both inside and outside the crater rim, caused by sharp rocks and block fields that are distributed over the entire crater area.  However, Mini-SAR has found craters near the north pole that have high CPR inside, but not outside their rims.  This relation suggests that the high CPR is not caused by roughness, but by some material that is restricted within the interiors of these craters.  We interpret this relation as consistent with water ice present in these craters.  The ice must be relatively pure and at least a couple of meters thick to give this signature.
      An “anomalous” crater on the floor of Rozhdestvensky (9 km Diameter, 84.3° N, 157° W), near the north pole of the Moon. This feature shows high CPR within the crater rim, but low CPR outside, suggesting that roughness (which occurs throughout a fresh crater) is not the cause of the elevated CPR. This feature’s interior is in permanent sun shadow. SC stands for “same sense, circular”, OC stands for “opposite sense, circular” and CPR is the “circular polarization ratio.” The histogram of CPR values clearly shows that interior points (red line) have higher CPR values than those outside the crater rim (green line). The estimated amount of water ice potentially present is comparable to the quantity estimated solely from the previous mission of Lunar Prospector’s neutron data (several hundred million metric tons.)  The variation in the estimates between Mini-SAR and the Lunar Prospector’s  neutron spectrometer is due to the fact that it only measures to depths of about one-half meter, so it would underestimate the total quantity of water ice present.  At least some of the polar ice is mixed with lunar soil and thus, invisible to our radar.
      “The emerging picture from the multiple measurements and resulting data of the instruments on lunar missions indicates that water creation, migration, deposition and retention are occurring on the moon,” said Paul Spudis, principal investigator of the Mini-SAR experiment at the Lunar and Planetary Institute in Houston. “The new discoveries show the moon is an even more interesting and attractive scientific, exploration and operational destination than people had previously thought.”
      “After analyzing the data, our science team determined a strong indication of water ice, a finding which will give future missions a new target to further explore and exploit,” said Jason Crusan, program executive for the Mini-RF Program for NASA’s Space Operations Mission Directorate in Washington.
      The Mini-SAR’s findings are being published in the journal Geophysical Research Letters. The results are consistent with recent findings of other NASA instruments and add to the growing scientific understanding of the multiple forms of water found on the moon. The agency’s Moon Mineralogy Mapper discovered water molecules in the moon’s polar regions, while water vapor was detected by NASA’s Lunar Crater Observation and Sensing Satellite, or LCROSS.
      Mini-SAR and Moon Mineralogy Mapper are two of 11 instruments on the Indian Space Research Organization’s Chandrayaan-1. The Applied Physics Laboratory in Laurel, Md., performed the final integration and testing on Mini-SAR. It was developed and built by the Naval Air Warfare Center in China Lake, Calif., and several other commercial and government contributors.
      Get more information about Chandrayaan-1
      March 2, 2010
      View the full article
    • By NASA
      NSYNC’s Lance Bass Shows How to Safely View a Total Solar Eclipse
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