Name: What is Climate Change? Crash Course Geography #14
Uploaded: 2022-06-23T11:17:55.000Z
Duration: 13 min
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

In 2018, I got to walk across the surface of a receding glacier in Iceland. From where

I stood, I could see a patch of snow and ice off in the distance -- the last remnants of

過去完了形

another glacier that had since melted away.

That ice-speckled area was all that remained of 800 year old Okjokull, or the Ok glacier,

which was officially declared dead in 2014 by Icelandic geologist Oddur Sigurðsson.

It once spanned an area as large as 38 square kilometers. 

In 2019, the loss of Okjokull was commemorated with a plaque on the site of the former glacier.

It's the first monument dedicated to a glacier lost to human-induced global warming.

Looking after our planet and all its dynamic ecosystems and landscapes -- including glaciers

-- is everyone's job. We know rising temperatures are correlated with rising carbon dioxide

in the atmosphere, and the amount of carbon dioxide generated by our day to day actions

can have an effect on the other side of the world. 

But while individual actions matter, who is emitting carbon dioxide is highly unequal.

About half of total US emissions in 2019 were direct emissions from corporations, coming

from sources like power plants and oil and gas production facilities. So they also have

Knowing who or what is emitting carbon dioxide is only part of understanding climate change.

We also study who emissions affect and the geographical impacts of a warming planet.

Climates are complex, so I don't have all the answers, but there's a lot we can learn.

I'm Alizé Carrère, and this is Crash Course Geography.

Even with a problem as complicated as climate change, we can start with a picture. Like

this picture of Muir Glacier in Alaska from 2004.

Pictures and maps can show us where land masses, oceans, and geographical features are located,

which is spatial information that we kinda take for granted. 

The Earth is dynamic, and we have to remember that both pictures and maps are really snapshots

of a particular time. So if we compared this image to past ones of the same area, we'd

see how it's changed and we could explore why change is happening here. 

A photo taken in 1941 from the exact same spot as the recent photo shows an entirely

different landscape. The glacier was much bigger. After looking at lots of old and new

photographs, current glaciological surveys, and the geologic record, we know glaciers

around the world, in places like Alaska, the Swiss Alps, and Mount Kilimanjaro, have shrunk

dramatically. Muir Glacier is just one example. 

To get deeper into the "why," we know that ice and snow melt faster as air temperatures

get warmer. But glaciers also depend on how much precipitation they get each year -- if

less snow accumulates, glaciers lose more ice on their bottom edge than they can replace

at the top. That precipitation comes from the hydrosphere, and its regional patterns

can depend on temperature and wind patterns over distant oceans.

So mountain landscapes have changed as climate patterns have changed, which ties back to

the global energy budget and insolation and the beginning of the Earth. It's a complicated problem.

The terms “climate change” and “global warming”  are often used interchangeably.

But even though these phenomena are closely related, there is a difference between them.   

Climate change is the change in average weather patterns in a region over a long period of

time. These changes can be natural or anthropogenic, meaning human induced. 

And when I say long, I mean each climate period can last for several decades or longer. For

example, there was a Little Ice Age that happened from 1300 to 1850 CE. Mountain glaciers expanded

worldwide and mean annual temperatures dropped by 0.6 degrees Celsius in the Northern Hemisphere.

That's a five hundred and fifty year climate pattern, which then changed to a different one.

On the other hand, global warming is the increase in the average surface temperature of our

planet. In our current period of global warming, there's been a well-documented rise of average

temperatures around the globe since the Industrial Revolution in the 17 and 1800s. 

So when scientists or leaders talk about “global warming”, they're almost exclusively referring

to this recent warming, which comes from human activities that increase greenhouse gases

emissions, like carbon dioxide, methane and nitrous oxide. They trap solar energy, so

That additional energy is changing not only the average temperature, but also climate

processes within the atmosphere and oceans. These include more extreme storms, heat waves,

droughts, changing regional temperature and precipitation patterns that cause vegetation

zones to shift, and glaciers to melt -- which results in sea level rise and changing coastlines.

Essentially, when the planet gets warmer, climates change. 

We know the Earth has had many different climates thanks to paleoclimatologists, who study past

climates through proxy data, or data that provide clues about the past. 

Comparing multiple proxies gives us a more complete picture of what happened and helps

us anticipate the changes we need to prepare for.

For example, they use tree rings that show dry and wet years, fossilized bugs that tell

us about moisture and temperature levels of bygone ecosystems, or deep-sea sedimentary

Like, the deep-sea sedimentary record shows that the Earth overall had one of two extreme

climates and glaciers advanced and retreated across the Earth at least 28 times during

We can see that when glaciers advance and the climate is colder, glaciation occurs and

sea levels drop. And when the climate is warmer, glaciers retreat, and sea levels rise, ushering

in an interglacial period. Which is what we're in right now.

One of the most useful kinds of proxy data for atmospheric conditions and how climates

changed year to year are ice core data. From ice, we can extract the chemical composition

of past atmospheres. Using special drills, paleoclimatologists have extracted long tubes

of ice from ice sheets and alpine glaciers all over the world, and estimated climates

going back at least 400,000 years. Let's go to the Thought Bubble.

On the top is fresh snow that fell this year and the year before and the year before that. Underneath

is the snow that fell when Marco Polo travelled the Silk Road and beneath that when the Buddha

And the deepest layers were laid down long before recorded history. 

The very bottom of ice sheets in places like Greenland and Antarctica have snow that fell

before the beginning of the last ice age, 115,000 years ago or more. 

Just like snow on a sidewalk can get compressed by boots into sheets of slippery ice, the

snow on ice sheets is compacted into huge solid masses. 

And buried in each layer of ice is evidence of past atmospheric conditions: tiny air bubbles,

Once an ice core is moved from the field to the lab, scientists use isotope dating to

tell whether the carbon dioxide in those frozen bubbles was released from burning materials

like wood or coal in the lithosphere, or if it was airborne during a nuclear explosion, or

if it was part of the natural cycling of carbon. 

Paleoclimatologists have collected polar ice core samples and analyzed historical air bubbles

from Greenland and Antarctica, tropical glaciers in the mountains of the Andes and Kenya, and

mid-latitude glaciers in the Alps and Himalayas. 

When all these data are lined up, scientists can compare them with each other and see atmospheric

trends, which in turn shows climate change over thousands of years. 

Analysis shows that it can take just a few decades to change from colder to warmer climate

That might not sound fast, but when you're a 4.5 billion year old planet like the Earth,