지구 온난화가 가져온 알래스카의 해안선 변화

기후가 뜨뜻해지면
'해수면이 올라와서 육지의 면적이 줄어들 수 있다는 것'
은 이제 모두의 상식이 되어버렸습니다.

26년의 시차를 둔 아래 두 장의 사진을 보시고 어디가 변했는지 맞춰보시기 바랍니다.

(눈에 보이는 건 흰색이 부분이 없어졌다는 것 정도가 아닐까요?
- 저도 물론 그랬으니까요 ^^)

1992.07.08 촬영

2018.10.05 촬영

(8월 보다 10월이 분명 더 추웠을텐데 눈이 다 사라졌네요.)

눈에 잘 보이시지 않으셨겠지만

해안선 자체에 큰 변화가 나타났습니다.

1992년에는 공항이 바다에서 어느정도 거리가 있었는데

2018년에는 바짝 붙었습니다.

(노란색이 변화된 해안선인데, 제가 마구마구 그냥 그렸습니다. 정확하지는 않습니다

와우~~ 공항이 바다하고 더 가까워졌어요~)

지구 온난화로 해수면 상승에 의해서만 육지 면적이 줄어들 줄 알았는데

여기에는 다른 요인이 작용하고 있었습니다.

NASA의 말을 빌면

1. 지구 온난화로 파도에 의한 침식을 막아주던 해안의 얼음들이 사라졌다.
(위 사진에서 보면 Beaufort Sea의 얼음들)

2.  육지의 영구 동토층이 녹아버려 파도에 의한 해안 침식에 취약해졌다.

결론적으로 보면

온난화로 인한 침식의 피해는

북위도의 영구 동토층 인근의 해안가 지역에서 먼저 나타나겠구나.

About 13 percent of the Alaskan landscape has changed in some way in recent decades. That’s the conclusion of a 2018 study led by Neal Pastick, who examined historical aerial photos and satellite images to identify areas of ecological change across the state.

“We set out to characterize all of these changes by using remote sensing data from the past 32 years,” said Pastick, a physical scientist and contractor to the U.S. Geological Survey Earth Resources Observation Science Center. “It’s striking how much change is happening, and what we can do with the Landsat satellites to link these changes into one cohesive story.”

The most notable changes in Alaska include the browning of land from forest fires and the greening of the land as vegetation regrows. Pastick also documented vast areas of land affected by erosion, including segments of coastline that have dramatically changed shape.

The images above show how erosion has eaten away at the northern coast of Alaska. They were acquired by the Landsat 4 satellite on July 8, 1992 (top), and the Landsat 8 satellite on October 5, 2018 (bottom). Use the image-comparison tool to note the retreat along the coast just east of Drew Point and north of the airport. (Note that changes in ice cover between images reflect a long-term trend, but also simple seasonal differences.) “This is a pretty extreme example of coastal erosion in Alaska,” Pastick said.

Warming temperatures have played a major role in the coastline retreat. Melting permafrost leaves the ground less stable and more prone to being washed away by heavy rains and pounding ocean waves. Rising temperatures cause the protective sea ice cover to disappear for longer periods each spring and summer, meaning waves and Arctic storms can more easily chew away at the coastline. No one lives along the receding coastline shown above, but coastal communities elsewhere in Alaska have had to make decisions about how to deal with failing infrastructure as permafrost melts and coastlines retreat.

Pastick and colleagues used satellite and aerial photograph comparisons to verify the type of ecological change responsible for broader trends in the landscape. For example, the map above shows the median change in the landscape’s wetness per year between 1984 and 2015. Analyzing all of the information together led them to conclude that 174,000 square kilometers (451,000 square kilometers) of the Alaskan landscape has undergone change.

More work is needed in order to identify how the changing landscape will continue to affect communities, according to Pastick. He added: “I want to understand how these evolving systems might change in the future, and what that change means for people who live there.”

NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey and NDVI and NDWI annual trend data courtesy of Neal Pastick. Story by Kathryn Hansen.

<출처 : NASA>