Arquivo da tag: Degelo

Climate Change Has Knocked Earth Off Its Axis (Gizmodo)

earther.gizmodo.com

Brian Kahn, 23 April 2021


A 3D portrait of methane concentrations and a slightly wobblier Earth.
A 3D portrait of methane concentrations and a slightly wobblier Earth.

Of all the things attributable to climate change, the rotational poles moving differently is definitely one of the weirder ones. But a new study shows that’s exactly what’s happening. It builds on previous findings to show that disappearing ice is playing a major role, and shows that groundwater depletion is responsible for contributing to wobbles as well.

The findings, published last month in Geophysical Research Letters, uses satellites that track gravity to track what researchers call “polar drift.” While we think of gravity as a constant, it’s actually a moving target based on the shape of the planet. While earthquakes and other geophysical activities can certainly play a role by pushing land around, it’s water that is responsible for the biggest shifts. The satellites used for the study, known as GRACE and GRACE-FO, were calibrated to measure Earth’s shifting mass.

They’ve previously detected gravity changes tied to disappearing ice in Antarctica and the drought that led to groundwater depletion in California in the mid-2010s. The data can also reveal how these changes in gravity, in turn, impact the poles.

Polar drift is something that happens naturally. The Earth’s axis is slowly shifting, but there’s been a marked acceleration in recent decades. The poles are now moving at nearly 17 times the rate they were in 1981, a fairly remarkable speed-up. What’s even more remarkable, though, is that poles actually began moving in a new direction quite suddenly in 2000, at a rapid clip.

Previous research used the same satellite data to observe the speed-up and change of gear and attributed it to ice loss in Greenland and West Antarctica as well as groundwater pumping. The new study extends the record back to the 1990s and explores some of the year-to-year wobbles in more detail. The findings point to changes in groundwater use in specific regions as the source of some of those differences.

“Using the GRACE data (for the period 2002-2015) we showed that such interannual signals (as these authors pointed out: kinks at 2005 and 2012) can be explained by the terrestrial water storage,” Surendra Adhikari, a scientist at NASA Jet Propulsion Laboratory who led the 2016 research, said in an email. “The new paper reinforces the statement by also showing that another kink in the polar motion data (at 1995) is also explained by total water storage variability, especially by the on-set of accelerated Greenland ice mass loss and depletion of water storage in the Middle East and the Indian subcontinent.

“In general, the paper (along with our previous works) reveals the strong connection between the climate variability and how the Earth wobbles,” he added, noting the new study was a “nicely done paper.”

In the scheme of things, climate change triggering polar movement isn’t too worrisome, given the other clear and present dangers like intense heat waves, ocean acidification, and the sixth mass extinction. Ditto for the role of groundwater depletion, which has the potential to impact billions of lives. But it’s a powerful reminder of just how much humans have reshaped the planet and why we should probably cut it out sooner than later if we don’t want our world to turn upside down.

Correction, 4/23/21, 6:30 p.m.: This post has been updated to reflect that the rotational poles are the ones in question moving and being studied.

West Antarctic melt rate has tripled in last decade (Science Daily)

Date: December 2, 2014

Source: University of California – Irvine

Summary: A comprehensive, 21-year analysis of the fastest-melting region of Antarctica has found that the melt rate of glaciers there has tripled during the last decade.

UCI and NASA glaciologists, including Isabella Velicogna and Tyler Sutterley, have discovered that the melt rate of glaciers in West Antarctica has tripled, with the loss of a Mt. Everest’s worth of water weight every two years. Credit: Michael Studinger / NASA

A comprehensive, 21-year analysis of the fastest-melting region of Antarctica has found that the melt rate of glaciers there has tripled during the last decade.

The glaciers in the Amundsen Sea Embayment in West Antarctica are hemorrhaging ice faster than any other part of Antarctica and are the most significant Antarctic contributors to sea level rise. This study is the first to evaluate and reconcile observations from four different measurement techniques to produce an authoritative estimate of the amount and the rate of loss over the last two decades.

“The mass loss of these glaciers is increasing at an amazing rate,” said scientist Isabella Velicogna, jointly of the UC Irvine and NASA’s Jet Propulsion Laboratory. Velicogna is a coauthor of a paper on the results, which has been accepted for Dec. 5 publication in the journal Geophysical Research Letters.

Lead author Tyler Sutterley, a UCI doctoral candidate, and his team did the analysis to verify that the melting in this part of Antarctica is shifting into high gear. “Previous studies had suggested that this region is starting to change very dramatically since the 1990s, and we wanted to see how all the different techniques compared,” Sutterley said. “The remarkable agreement among the techniques gave us confidence that we are getting this right.”

The researchers reconciled measurements of the mass balance of glaciers flowing into the Amundsen Sea Embayment. Mass balance is a measure of how much ice the glaciers gain and lose over time from accumulating or melting snow, discharges of ice as icebergs, and other causes. Measurements from all four techniques were available from 2003 to 2009. Combined, the four data sets span the years 1992 to 2013.

The glaciers in the embayment lost mass throughout the entire period. The researchers calculated two separate quantities: the total amount of loss, and the changes in the rate of loss.

The total amount of loss averaged 83 gigatons per year (91.5 billion U.S. tons). By comparison, Mt. Everest weighs about 161 gigatons, meaning the Antarctic glaciers lost a Mt.-Everest’s-worth amount of water weight every two years over the last 21 years.

The rate of loss accelerated an average of 6.1 gigatons (6.7 billion U.S. tons) per year since 1992.

From 2003 to 2009, when all four observational techniques overlapped, the melt rate increased an average of 16.3 gigatons per year — almost three times the rate of increase for the full 21-year period. The total amount of loss was close to the average at 84 gigatons.

The four sets of observations include NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites, laser altimetry from NASA’s Operation IceBridge airborne campaign and earlier ICESat satellite, radar altimetry from the European Space Agency’s Envisat satellite, and mass budget analyses using radars and the University of Utrecht’s Regional Atmospheric Climate Model.

The scientists noted that glacier and ice sheet behavior worldwide is by far the greatest uncertainty in predicting future sea level. “We have an excellent observing network now. It’s critical that we maintain this network to continue monitoring the changes,” Velicogna said, “because the changes are proceeding very fast.”


Journal Reference:

  1. Tyler C. Sutterley, Isabella Velicogna, Eric Rignot, Jeremie Mouginot, Thomas Flament, Michiel R. van den Broeke, Jan M. van Wessem, Carleen H. Reijmer. Mass loss of the Amundsen Sea Embayment of West Antarctica from four independent techniquesGeophysical Research Letters, 2014; DOI: 10.1002/2014GL061940