Latest / The Climate Translation / Nature's Savings Account

Transcript

Nature's Savings Account · The Climate Translation

0:00
If you ask someone to describe Earth from space, they'll probably say the same thing we
0:12
all learned as kids, it's the blue planet.
0:16
More than 70% of Earth's surface is covered by water.
0:20
Oceans stretch from horizon to horizon.
0:23
Clouds move enormous amounts of moisture around the globe.
0:27
From a distance, water seems almost limitless.
0:31
But appearances can be deceiving, because despite all that blue, the amount of fresh
0:37
water available to support nearly 8 billion people is surprisingly small.
0:43
Of the small amount that is fresh water, most of it's locked away as glaciers, snowpack
0:48
or underground.
0:50
And that means many freshwater systems that we depend on aren't really reservoirs at
0:55
all.
0:56
They're storage systems, natural savings accounts that collect water during colder, wetter periods
1:03
and release it when we need it most.
1:06
Today we're going to explore where Earth's freshwater actually comes from, why glaciers
1:11
are far more important than people realize, and what happens when some of our planets'
1:16
largest natural water storage systems begin to change.
1:22
Welcome back to the podcast, I'm Dr. Mac, and this is the Climate Translation.
1:34
When I teach introductory Earth science, I often start with a simple question.
1:39
How much of Earth's water do you think that humans can actually use?
1:44
The answers are usually all over the place... 20%, 30%, sometimes half.
1:50
Honestly, I understand why.
1:53
If you ever looked at a globe, the water seems everywhere.
1:58
Oceans dominate the map, lakes and rivers crisscross the continents.
2:03
Satellite images show clouds constantly moving moisture around the atmosphere.
2:09
The water here feels abundant.
2:12
But once you start doing the math, the picture changes quickly.
2:16
About 97% of all the water on Earth is saltwater, contained in our oceans.
2:23
That leaves only about 3% or less as freshwater.
2:27
Now, 3% of all the water on Earth is still a lot of water.
2:32
It sounds encouraging, but we still have to keep going, because most of that freshwater
2:36
isn't available to us either.
2:39
Nearly 70% of that 3% is locked away in glaciers and ice sheets, and in another
2:46
large portion exist as groundwater deep below the surface, often difficult to access.
2:54
That leaves only a tiny fraction in places we normally think about when we hear the word
2:59
fresh water: rivers, lakes, wetlands, and reservoirs.
3:05
The water we rely on every day is actually one of the smallest slices of the entire global
3:12
water budget on this planet.
3:14
I think one reason people find this surprising is because we tend to focus on where water
3:19
is visible.
3:21
You can see rivers and lakes and reservoirs.
3:25
But those are really just kind of like the checking account of the global water system.
3:30
Much of the water is stored somewhere else, and that's where glaciers become important.
3:37
When people hear the word glacier, they think of remote places, like Greenland and
3:42
Antarctica, and high mountain peaks far away from where people live.
3:47
But glaciers are much more than just giant blocks of ice.
3:52
They are storage systems.
3:54
In some ways they're nature's version of a savings account.
3:59
Every winter snow accumulates in high mountain regions.
4:03
If enough snow survives the summer melt season, it gradually is compacted into ice.
4:09
For years, decades, centuries, even millennia, glaciers store water that originally fell as
4:16
precipitation.
4:18
What makes glaciers remarkable is that they store not just water, but time.
4:24
Think about that a moment.
4:25
A snowflake that falls in the mountains today may not become river water for years, decades,
4:31
centuries.
4:32
The glacier acts like a delayed delivery system, slowly releasing water long after the
4:39
originally fell from the sky.
4:41
And that delayed release has consequences.
4:45
Because rivers don't need the most water during the wet season, they need it during the
4:50
dry season.
4:51
When rainfall is limited and temperatures are highest, when crops are growing and cities
4:56
need the most water, glaciers help bridge that gap.
5:01
They collect water during cold periods and release it during the warm periods.
5:06
And for thousands of years, many of the world's major river systems have depended on that
5:12
natural storage cycle.
5:15
So what happens when nature's savings account starts to shrink?
5:20
At this point, it might be tempting to think that some of the melting glaciers we see these
5:24
days, due to climate change, could actually solve some water shortages.
5:29
After all, if ice is turning into liquid water, shouldn't rivers be swelling and getting
5:34
more water?
5:36
And in a short term, that's exactly what happens.
5:39
This is where things become counterintuitive to people who don't really understand the
5:43
science.
5:45
Imagine you have a retirement account.
5:47
Under normal circumstances, you might live off the interest it generates.
5:52
The account remains stable as long as you're only spending what it earns in interest.
5:57
Now, imagine you start withdrawing some of the principal as well.
6:02
At first, life would be great.
6:05
You have more money than before and you can spend more freely.
6:08
But of course, there's a problem.
6:10
Your larger withdrawals are only possible because the account itself is getting smaller.
6:17
Glaciers behave in a similar way.
6:19
When a glacier loses mass, more water enters the nearby river.
6:24
And for a period of time, even a couple of years, stream flow can actually increase.
6:30
Communities downstream might see more water available during warm seasons and reservoirs might
6:35
receive larger inflows.
6:37
The system might appear healthy for a while, even as the glacier itself is shrinking.
6:43
Scientists refer to this period as increased runoff.
6:47
But eventually, something important happens.
6:50
The glacier itself is getting smaller, and the smaller glacier contains less ice available
6:56
to melt.
6:57
At some point, the system reaches what hydrologists call peak water.
7:03
Peak water is the moment when melt water production reaches its maximum.
7:08
After that point, the trend reverses.
7:11
The glacier continues melting, but because there's less ice, annual runoff begins to decline
7:18
year after year.
7:19
It's like cutting down a forest.
7:21
The first few years you might have a lot of lumber, but eventually there's fewer trees
7:26
left to harvest.
7:28
The same principle applies to stored ice.
7:31
And researchers are increasingly observing this pattern in mountain regions across the
7:36
world.
7:37
Some glacier-fed watersheds have already passed peak water.
7:42
Others are expected to reach it during this century.
7:46
The timing varies from place to place because every glacier is different.
7:50
Some are large and some are small.
7:52
Some exist in very cold climates, and others are experiencing rapid retreat.
7:58
But the underlying physics remains the same.
8:01
You can only withdraw stored water for so long, before that savings account begins to
8:06
run low.
8:07
Now our glaciers aren't disappearing everywhere overnight, and many river systems receive
8:13
water from multiple sources, including rainfall and seasonal snowpack and groundwater sources.
8:20
But the trend is significant because glaciers have historically provided something extremely
8:26
valuable: reliability.
8:29
They act as a buffer.
8:31
When a dry year occurs, glaciers continue to melt.
8:35
When precipitation is lower than normal, glaciers still release water into rivers.
8:40
They help smooth the natural ups and downs of the hydrologic cycle.
8:45
As those frozen reserves become smaller, the buffering capacity begins to weaken.
8:51
And this isn't just happening in one part of the world.
8:54
It's occurring across mountain ranges on every continent.
8:58
Which means the question is no longer whether glacier loss affects freshwater resources.
9:04
The question is how many people depend on those frozen reserves, and the answer turns out
9:09
to be a lot more than you might realize.
9:15
Glaciers don't exist in isolation.
9:18
They sit at the headwaters of some of the most important river systems on Earth.
9:23
In fact, many of the world's major rivers began as snow and ice in high mountain source
9:29
regions.
9:31
If you travel to South Asia, you find the Himalayas.
9:35
Sometimes called the Third Pole, because of the enormous mass of ice stored there.
9:41
These mountains feed river systems like the Indus, the Ganges, and the Brahmaputra.
9:46
Together these rivers support millions of people through agriculture, transportation,
9:52
industry, and drinking water supplies.
9:55
If you move west into Europe, you find the Alps.
9:59
The glaciers there feed rivers such as the Rhine, the Rhine, and the Po.
10:04
Rivers there have shaped trade routes, agriculture, and human settlement for centuries.
10:10
Since South America, the Andes become the story.
10:14
Communities from Colombia to Chile depend on the seasonal meltwater from the mountain glaciers,
10:19
particularly during the dry season when rainfall becomes scarce.
10:24
And in North America, the Rocky Mountains serve a similar role.
10:28
Snowpack and glacier-fed watersheds help supply water to major river systems that support
10:34
cities, the agriculture, recreation, and energy production across much of the United States
10:41
and Canada.
10:43
These are all different continents and climates, different cultures.
10:47
But they all have the same basic physics.
10:50
Water falls from the atmosphere, it becomes stored as snow and ice, and that stored water
10:56
is gradually released over time.
10:58
For generations, we've treated these frozen reservoirs like a permanent feature of the
11:04
landscape.
11:06
They were simply there, reliable, and predictable, and part of the background.
11:11
But scientists are observing these systems are changing.
11:15
One of the reasons glaciers receive so much scientific attention and news attention is because
11:21
they respond directly to long-term shifts in temperature.
11:26
Glaciers gain mass when snowfall exceeds melting, and they lose mass when melting exceeds
11:31
snowfall.
11:32
And when researchers begin comparing observations around the world, clear patterns have emerged.
11:39
Many glaciers are shrinking, not all, and not all at the same rate.
11:44
But enough of them that a global trend is unmistakable.
11:48
In fact, recent monitoring efforts have documented some of the largest glacier loss ever recorded.
11:56
Scientists tracking mountain glaciers worldwide have found that the past decade has contained
12:03
many of the most significant ice loss years in the observable record.
12:09
Now it's important to understand what all of this means.
12:13
When scientists talk about glaciers losing hundreds of billions of tons of ice, they're
12:19
not suggesting that every glacier on the planet is going to disappear.
12:24
Nor are they suggesting that every community dependent on glacier melt is going to face
12:28
an immediate crisis.
12:31
But what we are observing is a long-term reduction in the overall storage.
12:37
If we think back to our savings account analogy, the concern isn't the account is going to
12:41
be zero and close tomorrow.
12:44
It's that the withdrawals have consistently exceeded the deposits.
12:48
And year after year, decade after decade, the amounts have decreased.
12:53
Eventually, the trend changes what the account can provide.
12:57
And that's why glacier loss has become such an important climate indicator.
13:03
Glaciers integrate years of weather into a single signal.
13:08
A hot summer might cause additional melting.
13:10
A snowy winter might temporarily slow it down.
13:13
But over long periods of time, glaciers have revealed whether the balance is changing.
13:19
And increasingly, the balance appears to be shifting towards loss.
13:24
What makes this especially important is that glacier loss is not occurring by itself.
13:31
Many of the same regions experiencing shrinking glaciers are also facing growing populations,
13:37
increasing water demand, expanding agriculture, and in some cases, reoccurring severe drought.
13:45
In other words, our storage system, our savings account of the planet, is changing at the
13:50
same time human demand is continuing to grow exponentially.
13:56
And that combination brings us back to one of the best examples of how these forces
14:01
can interact: the American West.
14:05
One of the things I've learned after years of teaching meteorology and climate science
14:09
is that water problems are not always about how much water exists.
14:15
Sometimes it is about when the water arrives.
14:18
Imagine your employer suddenly decided to pay your salary in two large checks in April
14:24
and October, instead of spreading it across 12 months.
14:28
The total amount of money is still the same, but managing your finances might be more difficult.
14:34
You still have bills and February and November, and you still need money throughout the year,
14:39
it means you have to budget a lot more carefully.
14:43
Water systems work in a surprisingly similar way.
14:47
For centuries, snowpack and glaciers have helped regulate the timing of our water delivery.
14:53
Winter storms deposit snow in the mountains.
14:56
Some of that snow melts during the spring runoff.
14:59
Some become stored as glacier ice and released more gradually over time.
15:04
The result is a relatively steady flow of water into our rivers and reservoirs.
15:10
Nature, in a sense, is spreading out the payments.
15:14
But as mountain ice declines, and snowpack becomes less reliable in regions, the timing
15:20
has begun to shift.
15:22
More precipitation may arrive as rain, instead of snow.
15:25
More runoff may occur earlier in the year.
15:28
Less water may remain available during the hottest months when the demand is highest.
15:34
It creates a challenge for systems that were designed around older, more reliable patterns.
15:40
The Colorado River Basin is a great example.
15:43
When most people think about the river, they picture the canyons and the deserts.
15:48
But the river itself began hundreds of miles away in the mountains.
15:53
Historically, winter snow accumulated in the Rockies and then melted gradually through
15:58
the spring and summer.
16:00
Reservoirs such as Lake Powell and Lake Mead were built and designed around that seasonal
16:06
cycle.
16:07
The challenge facing water managers today is the cycle is not behaving the way it once
16:13
did.
16:14
Warmer temperatures have reduced the snowpack, and earlier snow melt has changed when water
16:20
enters the system.
16:22
Droughts now reduce how much of that water ultimately reaches reservoirs, and all of
16:27
this is happening at the same time that millions of people have moved to the southwest.
16:34
Large agricultural regions have sprung up, and growing cities such as Las Vegas continue
16:39
to depend on the river.
16:41
The issue isn't simply that there's less water, it's that the storage and delivery system
16:46
is becoming less predictable, and similar conversations are happening around the world.
16:53
Communities in the Andes are asking how to manage water supplies as their tropical glaciers
16:58
retreat.
16:59
Countries on the Himalayan River systems are studying how future changes and snow and
17:05
ice might affect their water availability, and European nations are evaluating how shrinking
17:11
Alpine glaciers will influence river flow, agriculture, and their hydropower production.
17:18
These are all different locations and climates, but they're all asking the same question.
17:24
How much water can we store, when will it arrive, and how reliable will it be in the
17:29
future?
17:31
One thing I think that's important to remember is that glaciers have never been the only
17:35
source of fresh water.
17:37
Our rainfall still matters.
17:39
Our groundwater still matters.
17:41
The snowpack and human management matters.
17:44
The future of fresh water isn't determined by glaciers alone, but glaciers have long
17:50
served as nature's most effective buffering systems.
17:54
They smooth out the dry years and sustain rivers during hot summers.
17:59
They have provided a reserve that could be drawn upon when conditions became difficult.
18:05
As the frozen reserves become smaller, some of the natural buffering capacity has begun
18:10
to weaken, and that means the timing, storage, and management of water has become more important
18:16
than it was before.
18:18
Ultimately, the challenge isn't simply having water.
18:22
It's having water available when and where people need it.
18:36
Our blue marble, the ocean planet Earth, has abundant water, but the reality is that the
18:41
available fresh water is a much more finite resource.
18:46
The water exists within a small and more delicate system of rivers, lakes, groundwater,
18:52
snowpack and glaciers.
18:54
For thousands of years, many of those systems operated within a fairly predictable rhythm.
19:00
Water fell to snow, accumulated in the mountains, and was gradually released as the seasons changed.
19:07
As climate change alters weather patterns and climate zones, glaciers, the savings accounts
19:12
from most of our available fresh water, are beginning to shrink.
19:17
Our rivers and lakes won't disappear overnight, but the timing, storage, and distribution
19:22
of the water that feeds them is changing.
19:25
And as those patterns change, society will have to adapt right alongside them.
19:31
We need to take note of the change we're seeing around us,
19:35
consider our response to that change, and plan for a future that may be very different
19:40
than our past.
19:42
I'm Dr. Mac, and this has been the Climate Translation.
19:46
If you have a question about the climate that you've been too afraid to ask, or if you
19:50
have a differing opinion, I want to hear from you.
19:53
I can use your viewpoint in a future episode.
19:55
You can reach me at theclimatetranslation at gmail.com.
20:00
I'll see you next time.