The Guardian
- Harold R Wanless
To avoid the grimmest outlook posed by warming oceans, we need to extract
heat-trapping gases from the atmosphere
|
The US army corps of engineers distributes sand along the beach
in Miami Beach, Florida. The project is part of a $16m scheme to
widen the beaches in an effort to fight erosion and protect
properties from storm surges.
Photograph: Joe Raedle/Getty Images
|
Author
Harold R Wanless
is professor of geography and regional studies at University of
Miami.
|
The climate emergency is bigger than many experts, elected officials, and
activists realize.
Humanity’s greenhouse gas emissions have
overheated the Earth’s atmosphere, unleashing punishing heat waves,
hurricanes, and other extreme weather – that much is widely understood.
The larger problem is that the overheated atmosphere has in turn overheated the
oceans, assuring a catastrophic amount of future sea level rise.
As oceans heat up the water rises in part because warm water expands but also
because the warmer waters have initiated major melt of polar ice sheets.
As a result, average sea levels around the world are now
all but certain to rise
by at least 20 to 30 feet. That’s enough to put large parts of many coastal
cities, home to hundreds of millions of people, under water.
The key questions are how soon this sea level rise will happen and whether
humans can cool the atmosphere and oceans quickly enough to prevent part of
this.
If seas rise 20 feet over the next 2,000 years, our children and their
descendants may find ways to adapt. But if seas rise 20 feet or more over the
next 100 to 200 years — which is our current trajectory – the outlook is grim.
In that scenario, there could be two feet of sea level rise by 2040, three feet by 2050, and
much more to come.
Two to three feet of sea level rise may not sound like much, but it will
transform human societies the world over. In south Florida, where I live,
residents
will lose access to fresh water. Sewage treatment plants will fail, large areas will persistently flood, and
Miami Beach and other barrier islands will be largely abandoned.
In
China, India, Egypt and other countries with major river deltas, two to three
feet of sea level rise will force the evacuation of tens of millions of people
and the loss of vast agricultural lands.
Attempting to limit sea level rise therefore must become an urgent priority,
including for the world leaders Joe Biden is inviting to a climate summit on
Earth Day, 22 April. We must reframe how the climate emergency is understood and
what it means to combat it.
Certainly, it is essential to meet the Paris agreement goal of
limiting temperature rise to 1.5 to 2C – but that will not be sufficient.
The solution to rapidly rising sea levels is twofold: humans must stop putting
more heat-trapping gases into the atmosphere,
and we must extract much
of what we’ve already put up there.
Since the Industrial Revolution
250 years ago, the amount of CO
2 in the atmosphere has soared due to
human activities, principally the burning of carbon-based fossil fuels.
To minimize future sea level rise, we need to lower that amount from
today’s 417 parts per million towards the 280 ppm that prevailed before
industrialization.
Halting heat-trapping emissions requires rapidly moving the economy off fossil
fuels to renewable energy as well as ending deforestation, shifting to
climate-friendly agriculture, planting soil-building forests, and more. But even
if we succeed on this front — and so far, we are falling well short — only the
atmosphere would stop getting hotter.
Cooling the oceans will be harder. This
requires pulling massive amounts of CO2
from both the atmosphere and the oceans and storing it where it cannot leak.
There are prototypes of such “carbon negative” technologies. Methods like
incorporating pulverized basaltic lava into fertilizers
can lead to CO
2 removal and other approaches must be aggressively
developed.
It is crucial that both strategies – halting further
emissions of CO
2 and extracting CO
2
that’s already been emitted – be pursued. Doing one cannot be an excuse for not
doing the other or we will fail.
Our dilemma is rooted in basic physics. Once CO
2
is emitted, it remains in the atmosphere for millennia, trapping heat and
warming the planet like a blanket warms a human body.
What’s insufficiently appreciated is that most of this warming
– over 93% – has
transferred to the oceans
and significantly warmed the upper 2,000 feet. This is accelerating polar ice
melt and global sea level rise and will continue to do so for centuries.
And sea level rise is accelerating at a dangerous pace. In 1900,
global sea levels were rising
0.6 millimeters a year. After 1930, as ocean warming and water expansion kicked
in, the rate of sea level rise doubled and doubled again, reaching 3.1mm a year
by 1990.
Since then, as ever-warmer oceans have driven polar ice
melt, the rate of sea level rise has quickened further. Today, oceans are rising
6 mm a year (
over two inches a decade), and this pace will continue to dramatically accelerate.
Two inches a decade may seem a trifle but remember: we are just at the beginning
of this acceleration. The
US National Oceanic and Atmospheric Administration projected
in 2017 that global mean sea level could rise five to 8.2ft by 2100.
Four years later, it’s clear that 8ft is in fact a moderate
projection. And regional influences – subsidence, changing ocean currents, and
redistribution of Earth’s mass as ice melts – will cause some local sea level
rise to be 20-70% higher than global.
Sea level rise of 8ft would be catastrophic. Absent extensive and very expensive
adaptation measures, it would put much of New York and Washington DC, Shanghai
and Bangkok, Lagos, Alexandria and countless other coastal cities underwater.
It would submerge south Florida. And building sea walls won’t help
in south Florida: the land rests on porous limestone, so rising seas will simply
seep under. Even the levee-protected Netherlands and New Orleans will be in deep
trouble.
Worse, on current trends, we will be lucky for seas to rise “only” 8ft by 2100.
The reason is that the computer models used by Noaa and others do not reflect
what we know about how seas have risen in the past.
These models
assume that sea level rise unfolds gradually, but the
geological record shows
that in fact it can occur in rapid pulses.
Warmer temperatures
following the previous ice age caused disintegration of one polar ice sector
after another, causing seas to rise in pulses of three to 30ft per century.
Today, accelerating ice melt in Greenland and Antarctica are almost certainly
the beginning of a new pulse of rapid sea level rise.
It is urgent that humanity transition to renewable energy, stop burning fossil
fuels, and develop and deploy technologies to extract CO
2 from the
skies and seas. We must also get realistic about adapting to the sea level rise
that can no longer be prevented.
Rather than building more in
low-lying regions and spending public money on coastal defenses that are bound
to fail, we should prepare to assist the eventual relocation of people and
infrastructure from the most threatened areas (and clean the land before
inundation).
Without such measures, there will come a point, sooner than many people realize,
when civilization as we know it will greatly weaken or outright collapse. We can
only prevent this scenario with serious planning, funding, and effort. Our
children, and their children, deserve much better than we are doing now.
Links
