1. VOA英语学习网
  2. 设首页|英语四级|千亿国际文娱网页版|英语日志|英文自我引见|英语话剧脚本
  3. 打包下载 | 千亿国际 | BBC打包 | 日语 韩语
  4. 手机版
  1. 千亿国际文娱
  2. 剑桥英语测验认证
  3. 外教口语面临面课程

TED迷信:克里斯汀·波伊娜:格陵兰冰原之下的机密

宣布工夫:2018-08-10内容泉源:VOA英语学习网

TED迷信:Kristin Poinar: What's hidden under the Greenland ice sheet?

When was I was 21 years old,I had all this physics homework.Physics homework requires taking breaks,and Wikipedia was relatively new,so I took a lot of breaks there.I kept going back to the same articles,reading them again and again,on glaciers, Antarctica and Greenland.How cool would it be to visit these placesand what would it take to do so?Well, here we areon a repurposed Air Force cargo planeoperated by NASAflying over the Greenland ice sheet.There's a lot to see here,but there's more that is hidden,waiting to be uncovered.What the Wikipedia articles didn't tell meis that there's liquid waterhidden inside the ice sheet,because we didn't know that yet.

I did learn on Wikipediathat the Greenland ice sheet is huge,the size of Mexico,and its ice from top to bottomis two miles thick.But it's not just static.The ice flows like a riverdownhill towards the ocean.As it flows around bends,it deforms and cracks.

I get to study these amazing ice dynamics,which are located in one of the mostremote physical environmentsremaining on earth.To work in glaciology right nowis like getting in on the ground floorat Facebook in the 2000s.

(Laughter)

Our capability to fly airplanesand satellites over the ice sheetsis revolutionizing glaciology.It's just starting to do for sciencewhat the smartphonehas done for social media.

The satellites are reportinga wealth of observationsthat are revealing new hidden factsabout the ice sheets continuously.For instance, we have observationsof the size of the Greenland ice sheetevery month going back to 2002.You can look towards the bottomof the screen hereto see the month and the year go forward.You can see that some areasof the ice sheet meltor lose ice in the summer.Other areas experience snowfallor gain ice back in the winter.This seasonal cycle, though, is eclipsedby an overall rate of mass lossthat would have stunneda glaciologist 50 years ago.We never thought that an ice sheet couldlose mass into the ocean this quickly.Since these measurements began in 2002,the ice sheet has lost so much icethat if that water were piled upon our smallest continent,it would drown Australia knee-deep.How is this possible?Well, under the ice lies the bedrock.We used radar to image the hills,valleys, mountains and depressionsthat the ice flows over.Hidden under the ice sheet are channelsthe size of the Grand Canyonthat funnel ice and wateroff of Greenland and into the ocean.

The reason that radarcan reveal the bedrockis that ice is entirelytransparent to radar.You can do an experiment.Go home and putan ice cube in the microwave.It won't melt,because microwaves, or radar,pass straight through the icewithout interacting.If you want to melt your ice cube,you have to get it wet,because water heats up easilyin the microwave.That's the whole principlethe microwave oven is designed around.Radar can see water.And radar has revealeda vast pool of liquid waterhidden under my colleague Olivia,seven stories beneath her feet.Here, she's used a pumpto bring some of that waterback to the ice sheet's surface.

Just six years ago, we had no ideathis glacier aquifer existed.The aquifer formedwhen snow melts in the summer sunand trickles downward.It puddles up in huge pools.From there, the snow acts as an igloo,insulating this waterfrom the cold and the wind above.So the water can stayhidden in the ice sheetin liquid form year after year.The question is, what happens next?Does the water stay there forever?It could.Or does it find a way outto reach the global ocean?One possible wayfor the water to reach the bedrockand from there the oceanis a crevasse, or a crack in the ice.When cracks fill with water,the weight of the waterforces them deeper and deeper.This is how fracking worksto extract natural gasfrom deep within the earth.Pressurized fluids fracture rocks.All it takes is a crack to get started.

Well, we recently discoveredthat there are cracks availablein the Greenland ice sheetnear this glacier aquifer.You can fly overmost of the Greenland ice sheetand see nothing,no cracks, no features on the surface,but as this helicopterflies towards the coast,the path that water would takeon its quest to flow downhill,one crack appears,then another and another.Are these cracks filled with liquid water?And if so, how deepdo they take that water?Can they take it to the bedrockand the ocean?To answer these questions,we need somethingbeyond remote sensing data.We need numeric models.

I write numeric modelsthat run on supercomputers.A numeric modelis simply a set of equationsthat works together to desCRIbe something.It can be as simpleas the next number in a sequence —one, three, five, seven —or it can be a more complexset of equationsthat predict the futurebased on known conditions in the present.In our case, what arethe equations for how ice cracks?Well, engineers already havea very good understandingof how aluminum, steel and plasticsfracture under stress.It's an important problem in our society.And it turns outthat the engineering equationsfor how materials fractureare not that differentfrom my physics homework.So I borrowed them, adapted them for ice,and then I had a numeric modelfor how a crevasse can fracturewhen filled with water from the aquifer.This is the power of math.It can help us understandreal processes in our world.

I'll show you nowthe results of my numeric model,but first I should point outthat the crevasse is abouta thousand times narrower than it is deep,so in the main panel here,we've zoomed in to better see the details.You can look to the smallerpanel on the rightto see the true scalefor how tall and skinny the crevasse is.

As the aquifer waterflows into the crevasse,some of it refreezesin the negative 15 degree Celsius ice.That's about as coldas your kitchen freezer.But this loss can be overcomeif the flow rate in fromthe glacier aquifer is high enough.In our case, it is,and the aquifer water drives the crevasseall the way to the base of the ice sheeta thousand meters below.From there, it has a clear pathto reach the ocean.So the aquifer water is a partof the three millimetersper year of sea level risethat we experience as a global society.

But there's more:the aquifer watermight be punching above its weight.The ice flows in complex ways.In some places, the ice flows very fast.There tends to be waterat the base of the ice sheet here.In other places, not so fast.Usually, there's not waterpresent at the base there.

Now that we know the aquifer wateris getting to the base of the ice sheet,the next question is:Is it making the ice itselfflow faster into the ocean?We're trying to uncover these mysterieshidden inside the Greenland ice sheetso that we can better planfor the sea level rise it holds.The amount of icethat Greenland has lost since 2002is just a small fractionof what that ice sheet holds.

Ice sheets are immense, powerful machinesthat operate on long timescales.In the next 80 years, global sea levelswill rise at least 20 centimeters,perhaps as much as one meter,and maybe more.Our understandingof future sea level rise is good,but our projections have a wide range.It's our role as glaciologistsand scientiststo narrow these uncertainties.

How much sea level rise is coming,and how fast will it get here?We need to know how much and how fast,so the world and its communities canplan for the sea level rise that's coming.

Thank you.

(Applause)

来自:千亿国际文娱网页版_千亿国际文娱|www.qy449.com 文章地点: http://www.tingvoa.com/html/20180810/Kristin-Poinar-Whats-hidden-under-the-Greenland-ice-sheet.html