A CHANGING ANTARCTICA: HOW COMPUTER MODELS HELP SCIENTISTS LOOK INTO THE FUTURE

As the temperature of the Earth warms, ice in Antarctica melts. As ice ﬂows off the land and into the sea around the edges of Antarctica, warm ocean waters melt the ice from below. Warm air also melts ice at the surface. This melting ice raises sea levels around the world, ﬂooding our coasts and causing serious damage to our buildings and roads. We do not know exactly how much warmer our world might get in the future


WHY DO WE CARE ABOUT ANTARCTICA?
The Antarctic ice sheet is a very special place on Earth.It is a continent

ICE SHEET
A very large and thick body of ice that covers a vast land surface.Today's ice sheets are the Greenland and Antarctic ice sheets.
that is almost entirely covered by a thick layer of ice.Antarctica is about twice the size of Australia, .times the size of the United States, and bigger than all the European countries combined!Because of its massive size and very thick ice, Antarctica contains more than % of all ice on Earth.This is a lot of ice!As Earth's temperature gets hotter, some of the ice in Antarctica will melt, just like an ice cube melts on a hot summer day and creates a small water puddle (Figure ).When the ice in Antarctica melts, most of the water goes into the ocean, causing sea-level rise.Even though it is frozen, the ice also flows very slowly

SEA-LEVEL RISE
The measured height of water in the ocean.This changes constantly because of multiple factors, including how much ice melts from Antarctica.
from the center of Antarctica to the coasts, and the ice flows faster as the climate warms, meaning that even more ice reaches the edges of the land and melts into the oceans.What worries scientists is that there could be a "tipping point" after which Antarctica might melt faster and faster, more quickly than we could control or adapt to (Read more here).Higher seas mean that some cities are at risk of being under water.We already see that some cities flood more often than they used to, a ecting more than one billion people in , worldwide.

WHAT IS A MODEL OF ANTARCTICA?
A model is a representation of something.An example of a model is a castle that you build from building blocks, like Legos or Minecraft.Your creation will have all the important parts of what makes a castle: it can have towers, a drawbridge, and protective walls.In the end, your model castle will be di erent from a real castle, but it will be made up of similar parts.that falls on the ground and removing the snow that melts.
The early models of Antarctica were similar to giant snowballs.Scientists would keep track of how much snow had fallen and should be added to the giant snowball over time, or how much snow should be removed because it was getting warmer.But as scientists continued to study and understand Antarctica, they realized that a giant snowball was a bad model of Antarctica.A better model is very cold syrup or honey that you pour on pancakes!This is because Antarctica, like cold syrup, does not keep the same shape over time.Ice slowly flows and slides over the land underneath and, by doing so, it spreads out and gets thinner.Next time you are in the kitchen, pour cold honey or syrup on a plate, and you will see it slowly spread out and get thinner.Antarctic ice does the same thing-but much more slowly!So, a good way to describe how Antarctica's ice moves in space and time is to treat it as a very cold, sticky liquid.And that is exactly how scientists treat ice in today's ice sheet models.Of course, we must still keep track of how much snowfall to add to the model, to know how much the ice should grow-this is like knowing how much syrup or honey is poured onto your plate.We must also understand how quickly the ice that is touching the ocean is melting (Figure ).But now our ice sheet model also knows that the ice that is added due to snowfall also needs to slowly spread.The ice sheet models that scientists create try to capture all that we know about Antarctica and, as scientists learn new things about ice, we update our models.

WHY DO WE NEED COMPUTER MODELS OF ANTARCTICA?
Scientists use computer models to make predictions about what the future will look like or what the past was like.These models help us to understand how Antarctica could change in shape and size under many possible temperatures and climates.Our models also help us test ideas, for example, whether we can slow down sea-level rise if Earth's temperatures do not rise as fast as they have recently.
To make projections (predictions) about the future, we also need to frozen) to the very hard ground, or is the ice sliding over very soft ground?When scientists try to understand what Antarctica will look like in the future, they may use an ice sheet model to check what would happen if the ice was sliding, compared to if the ice was frozen to the ground.Scientists can run the model with as many di erent setups as they can think of, and this will allow them to explore the range of future possibilities.

WHAT WILL ANTARCTICA LOOK LIKE BY THE END OF THE CENTURY?
To see what Antarctica could look like in the year , a big group of scientists from all around the world used di erent computer models of Antarctica to run the same set of experiments [ ].To run these ice sheet models, they need to know, how much snow will be falling on top of the ice sheet and how warm the ocean will be around the edges of the ice.These two things come from a di erent type of model: a climate model.These are computer models of the whole

CLIMATE MODEL
A computer model of the whole Earth.It uses the amount of greenhouse gases in the air as input and calculates how much the air and ocean will warm.
Earth (Read more here) that can be used to understand how much the air and ocean will warm up, depending on the amounts of greenhouse gases that are added to the atmosphere.The Antarctica ice sheet

GREENHOUSE GASES
Gases in the atmosphere that can warm Earth's climate.Many of these gases are the result of human activities, such as the carbon dioxide coming from burning fossil fuels.model experiments looked at two possible future climate scenarios: one in which people continue to release greenhouse gases the way that we currently do ("high emissions") and one in which people limit greenhouse gas emissions ("low emissions").In the end, ice sheet modeling groups took part in these experiments and their projections for how much sea-level rise could come from Antarctica are shown in Figure [ , ].You can see that the ice sheet models do not all agree on the future of Antarctica, and this is because of di erences in both the climate and the ice sheet models.Most ice sheet models show that Antarctica will continue to lose ice and increase sea level, but some models also show that perhaps there will not be very much change.In fact, some ice sheet models predict that Antarctica will grow over time!Although all climate models say that the atmosphere and ocean around Antarctica will warm up, the future for Antarctica is not certain because the climate models may not agree on where or when the warming will happen.And it gets even trickier: some climate models predict that, in a warmer world, we may get more snow over Antarctica, but others predict that we may get more rain.More snow means that some parts of Antarctica may get bigger and gain ice; on the other hand, more rain could lead to melting at the surface of the ice or help break up the ice.Warmer oceans always lead to ice being lost but, in the end, the future of Antarctica depends on whether the ice loss (due to warm ocean water or melting at the ice surface) is greater than any ice gained by more snow.

CONCLUSION
Antarctica could contribute a lot to sea-level rise in the future because it holds a lot of ice.To predict how much the sea level could rise and when this might happen, scientists create computer models of Antarctica's large ice sheet.Scientists put all their knowledge into building the ice sheet models, but each model is slightly di erent because there is a lot that we still do not know about Antarctica.The future of Antarctica also depends on how the atmosphere and ocean will change in a warming world.The models do not all agree, so the future of Antarctica is really not clear.To improve the clarity of Antarctica's future, we must continue taking measurements around Antarctica and using these measurements to improve computer models.Until then, we can also try to limit the warming that the Earth is seeing.Ice always melts when it is warm, but we can try to slow down the melting as much as possible.

YOUNG REVIEWERS
AVA, AGE: I am years old and in the fifth grade.I enjoy science as I get to spend time with people like me and explore science on field trips.I want to join the science field and join NASA as an astronaut.

ISABEL NIAS
Isabel Nias is a lecturer in glaciology at the University of Liverpool, UK.She is interested in calculating uncertainty in ice sheet model predictions, and how we can use satellite observations to reduce this uncertainty.She was super excited to be able to set foot on Antarctica and have a snowball fight.

FigureFigure
Figure OLIVIA, AGE: I am a student at YSA and a member of the Student Government Association.Science is one of my greatest passions, specifically environmental and forensic science.I hope to change the world one day, and contribute to making it a better place!QUINN, AGE: I am years old and in the th grade.I love to travel, try new foods, and I like reading murder mysteries!I have one little brother, a dog, and baby ducklings.
an Empire Innovation Professor at the University at Bu alo, USA.She uses models and observations of the ice sheets to understand how they may change in the future.She has a piece of Antarctica named after her, the Nowicki Foreland, that she hopes to day visit and have a snowball fight.*sophien@bu alo.eduDENIS FELIKSON Denis Felikson is a research scientist at NASA's Goddard Space Flight Center in Greenbelt, MD, USA.He studies the ice sheets and sea-level change using satellite measurements and models.Other icy things that he likes are ice skating, ice cream, and snowball fights.