by Jordan Wilkerson

figures by Michael Gerhardt

When someone asks you to consider the impacts of climate change, what do you think of? There’s a good chance that melting ice sheets comes to mind pretty quickly. For that reason, a recent finding regarding the trend in Antarctic ice is quite perplexing; the ice sheet is reportedly increasing in size! This is according to a research study conducted by a NASA team and published in Journal of Glaciology in October 2015 [1].

What’s the Evidence that the Antarctic is Getting Larger?

Antarctica is a colossal landmass far from human civilization. How was this research team able to determine changes in the amount of ice each year? Well, they used a nifty device called a LIDAR altimeter (Figure 1). Using this, they were able to determine the ice trend by measuring the changes in surface height over time.

A LIDAR, a portmanteau of light and radar, altimeter is just like a radar. A RAdio Detection And Ranging (radar) device emits radio waves that then bounce back once they hit some sort of physical barrier – such as a big rock. Because we know how fast radio waves move, if we measure how long they take to bounce off that big rock and come back to us, we can determine how far away the rock is [2].

Placed on a satellite orbiting Earth, the LIDAR altimeter instead sends ultraviolet and visible light waves down to the Antarctic surface and patiently waits for their return. Using LIDAR measurements recorded over time, the research team determined that from 1992-2001, the Antarctic ice sheets gained an average of 112 billion tons of ice each year. From 2003-2008, this number decreased to 82 billion tons [1].

How can the planet be experiencing a warming trend and have regions that are accumulating ice? This is a fair question. Another tempting question to ask is this: is the planet even experiencing a warming trend if the Antarctic ice sheet is getting bigger? Let’s address that question first.

So is Climate Change Even Happening?

Yes, it is. But before we go over the evidence supporting climate change’s existence, we should keep something in mind: the notion that there’s net ice gain in the Antarctic is still being debated among top scientists. For example, many esteemed glaciologists, such as University of Washington’s Dr. Ben Smith, have pointed out that the LIDAR altimeter used in the study might register snowpack as increased surface height even though that’s not really a permanent component of the ice sheet (Figure 1). Across large swaths of land surface, this small contribution could propagate into an apparent enormous gain in ice mass that’s not really there [3]. But unlike this study’s conclusions, the notion that humans are causing climate change is well established by a portfolio of lab experiments, theoretical models, and observational data [4].

First, there’s the rising temperature and its relationship with carbon dioxide. Gases in our atmosphere, particularly carbon dioxide (CO 2 ), largely dictate the temperature of our planet. How this happens has been known for over a century – this is not recent stuff [5]. In short, CO 2 acts as a heat-trapping blanket that envelops the planet. This blanket gets thicker and thicker as we emit more of this greenhouse gas into the atmosphere [6].

The effect of CO 2 on Earth’s surface temperature isn’t just based on a collection of calculations and lab experiments (an extensive collection, mind you). Scientists have assessed hundreds of thousands of years of temperature and CO 2 records. While there are some subtleties to the data, one clear trend emerges: the more CO 2 there is in the air, the hotter our planet becomes [7,8,9]. This relationship is still true today. Temperature elevations over the past century match well with the rising CO 2 levels since the Industrial Revolution [7].

Furthermore, while the Antarctic ice sheet is indeed increasing in size, this is not true for its northern counterpart, the Arctic. And the ice gain in the Antarctic doesn’t cancel out the ice loss in the Arctic. The Antarctic has gained about 7,300 square miles of ice each year since the late 1970s. The Arctic, on the other hand, has lost about 20,800 square miles of ice each year in that same period [10]. Global ice loss is still occurring on a significant scale.

Then What is Going On in Antarctica?

The measuring technique mentioned earlier gives us more than just what the ice gain is; it tells us where the ice is building up and where it’s receding. Using this insight, the NASA team concluded the culprit behind the net ice gain is East Antarctica. It is there and the interior of the West Antarctic ice sheet where gains are occurring. There is ice loss still occurring at the periphery of West Antarctica; it’s simply that the ice gains in the other regions are greater in magnitude [1] (Figure 2).

According to the authors of the study, the ice loss and ice gain have different causes. The ice gains in the East Antarctic are not a new trend. Its cause is essentially the change in climate at the end of the last ice age – around 10,000 years ago. When the ice age ended, the planet overall became warmer. With increasing warmth comes increasing ability of air to retain moisture.

The warmer, thus wetter, air provided the Antarctic with additional snowfall. This snowpack has been accumulating and compacting for thousands of years on the East Antarctic Ice Sheet, causing a build up of ice [1]. The West Antarctic ice loss trend is new, abrupt, and began after the Industrial Revolution. Its tie to human activity has been demonstrated through a large number of both observations and theoretical models [11].

An important thing to note is that the ice gains in the East Antarctic have been constant. Every year, the region gains around 200 billion tons according to the NASA study [1]. This is a steady ice gain. Yet, if you recall, the net ice gain cited in that study went down from 112 billion tons to 82 billion tons per year. What’s causing the decrease? As the map of the Antarctic shows, while the East Antarctic ice gains have remained relatively steady, the ice loss in the West Antarctic is accelerating each year. By this, I mean the amount of ice lost each year is typically greater than the year before.

An important clarification to make: this trend in ice loss in the West Antarctic is one conclusion of the NASA study not being debated. “We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” Jay Zwally, lead author of the study said. Therefore, if the increasing rates of ice loss in the West Antarctic continue, it’ll be only a few decades before they outweigh the ice gain in the East [12].

In this respect, there is no dispute. Antarctic ice is soon going to behave how we’d expect it to on a warming Earth – if it isn’t already. And when you’re considering how this study fits in with climate change, that is the important conclusion to keep in mind.

Jordan Wilkerson is a third year graduate student in the Department of Chemistry at Harvard University.

References

[1] Zwally, J., et. al., 2015. Mass gains of the Antarctic ice sheet exceed losses. Journal of Glaciology 61:1019-1036.

[2] Brit Lab. How does RADAR Work? (2013) https://www.youtube.com/watch?v=ywDE57CtaTM

[3] Howard, Brian Clark. What Antarctica’s Incredible “Growing” Icepack Really Means. National Geographic. (2015). http://news.nationalgeographic.com/2015/11/151103-antarctic-ice-growing-shrinking-glaciers-climate-change/

[4] Scientific consensus: Earth’s climate is warming. NASA. http://climate.nasa.gov/scientific-consensus/

[5] The Carbon Dioxide Greenhouse Effect. The Discovery of Global Warming. https://www.aip.org/history/climate/co2.htm

[6] A Blanket Around the Earth. NASA. http://climate.nasa.gov/causes/

[7] Understanding Climate Change: A Primer. Woods Hole Research Center. http://whrc.org/publications-data/understanding-climate-change-a-primer/

[8] Temperature Change and Carbon Dioxide Change. NOAA. (2008). https://www.ncdc.noaa.gov/paleo/globalwarming/temperature-change.html

[9] CO2 lags temperature – what does it mean? Skeptical Science. http://www.skepticalscience.com/co2-lags-temperature-basic.htm

[10] Ramsayer, K. Antarctic Sea Ice Reaches New Record Maximum. NASA. https://www.nasa.gov/content/goddard/antarctic-sea-ice-reaches-new-record-maximum

[11] Oppenheimer, M, Alley, RB. The West Antarctic Ice Sheet and Long Term Climate Policy. Climatic Change. 64: 1–10, 2004. https://www.princeton.edu/step/people/faculty/michael-oppenheimer/research/Oppenheimer-Alley-04.pdf

[12] Mass gains of Antarctic Ice Sheet greater than losses. Science Daily News. http://www.sciencedaily.com/releases/2015/10/151030220523.htm

Cover image from Andreas Kambanis and licensed under Creative Commons.