Defense

advantage. Napoleon’s disastrous winter campaign in Russia immediately comes to mind as an example of the former, while the American Revolutionary War provides examples of the latter.

In his splendid, Pulitzer Prize-winning biography of John

Adams, David McCullough recounts how the Colonial army mounted

an expedition during the winter of 1775–76 to take cannons captured

by Ethan Allen at Fort Ticonderoga on Lake Champlain and “haul the

great guns back over the snow-covered Berkshire Mountains all the

way to Boston, a task many had thought impossible.”2 By early March,

however, General George Washington’s men had positioned the guns

on the Dorchester hills “looking over Boston Harbor and the British

fleet,” which shortly sailed away in ignominious defeat and abandoned Boston. 

Bringing the cannons to Boston, McCullough wrote, was “a feat

of almost unimaginable daring and difficulty and, ironically, only

made possible by the severity of the winter, as the guns had been

dragged over the snow on sleds.”

Grim winters marked the incipient years of the Revolutionary

War. The following winter, Washington crossed the Delaware River in

driving sleet and snow to surprise the Hessians at the Battle of Trenton. Emanuel Leutze’s famous painting depicts Washington’s men

pushing hunks of ice in the frozen Delaware, which rarely freezes

today. The winter after that, Washington’s men endured their ordeal

at Valley Forge, emerging as a more confident army. 

It was about this bitterly cold era that Thomas Paine wrote,

both literally and metaphorically: “These are times that try men’s

souls. The summer soldier and the sunshine patriot will, in this crisis, shrink from the service of his country.” 

It is now known that the Revolutionary War took place within a

climatological era known as the “Little Ice Age,” a period beginning

about 1350 A.D. in which average wintertime temperatures abruptly

turned cooler in the North Atlantic region, and persisted that way for

roughly 500 years.

All human endeavor hinges on the vicissitudes of climate, and

that includes warfare. Recent evidence points to the potential for

abrupt cooling in the North Atlantic region in the future. Lest military planners be caught with summer soldiers during a big chill, they

Overview

Most debates and studies addressing potential climate change

have focused on the buildup of industrial greenhouse gases in the

atmosphere and a gradual increase in global temperatures. But

this “slow ramp”1 climate change scenario ignores recent and

rapidly advancing evidence that Earth’s climate repeatedly has

become much colder, warmer, wetter, or drier—in time spans as

short as three to 10 years.

Earth’s climate system appears to have sensitive thresholds,

the crossing of which shifts the system into different modes of

operation and triggers rapid, non-linear, and not necessarily

global changes. This new paradigm of abrupt climate change does

not appear to be on the radar screens of military planners, who

treat climate change as a long-term, low-level threat, with mostly

sociological, not national security, implications. But intense and

abrupt climate changes could escalate environmental issues into

unanticipated security threats, and could compromise an unprepared military. 

The global ocean circulation system, often called the Ocean

Conveyor, can change rapidly and shift the distribution patterns of

heat and rainfall over large areas of the globe. The North Atlantic

region is particularly vulnerable to abrupt regional coolings

linked to ocean circulation changes. Global warming and ocean

circulation changes also threaten the Arctic Ocean’s sea ice cover.

Beyond the abrupt climatic impacts, fundamental changes in

ocean circulation also have immediate naval implications.

Recent evidence suggests that the oceans already may be

experiencing large-scale changes that could affect Earth’s climate. Military planners should begin to consider potential abrupt

climate change scenarios and their impacts on national defense.

A Climate of War

History is filled with examples of military leaders who have suffered at the mercy of climate conditions that they failed to contemplate adequately, or who have exploited climate conditions to great

Global Warming Could Have a

Chilling Effect on the Military

by Richard F. Pittenger and Robert B. Gagosian

A publication of the

Center for Technology and National Security Policy

National Defense University

OCTOBER 2003

Number 33

Horizons

October 2003 Defense Horizons 1
Rear Admiral Richard F. Pittenger, USN (Ret.) is Vice President for Marine

Operations at Woods Hole Oceanographic Institution (WHOI) in Woods Hole,

Massachusetts. His 37-year career in the US Navy included posts as Oceanographer of the Navy and Director of Antisubmarine Warfare. He can be reached

at rpittenger@whoi.edu.

Robert B. Gagosian is President and Director of WHOI. In January 2003,

he chaired a panel on abrupt climate change at the World Economic Forum in

Davos, Switzerland. He can be reached at rgagosian@whoi.edu.

would do well to pay attention to recent scientific advances in our

understanding of the oceans and climate change.

Role of Oceans in Climate Change

Abrupt climate changes are possible, perhaps even more

likely, in the future, according to a 2002 report by the US National

Academy of Sciences (NAS), titled Abrupt Climate Change:

Inevitable Surprises.

3

The report cited wide-ranging geological evidence and computer models that demonstrate that Earth’s complex and dynamic

climate system has more than one mode of operation. Each mode

produces different climate patterns.

The evidence also shows that Earth’s climate system has sensitive thresholds. Pushed past a threshold, the system can jump

quickly from one stable operating mode to a completely different

one—“just as the slowly increasing pressure of a finger eventually

flips a switch and turns on a light,” according to the NAS report.

The same characteristics seem to be true of the global system of

ocean currents, collectively known as the Ocean Conveyor. A swift

reorganization of ocean circulation is a highly plausible mechanism

to induce large, abrupt climate change.4 Indeed, it is a prime suspect.

The Ocean Conveyor moves vast quantities of heat around our

planet, and thus plays a fundamental role in governing Earth’s climate. The oceans also play a pivotal role in the distribution and

availability of life-sustaining water throughout our planet. 

The oceans are, by far, the planet’s largest reservoir of water.

Evaporation from the ocean transfers huge amounts of water vapor to

the atmosphere, where it travels aloft until it cools, condenses, and

eventually precipitates in the form of rain or snow. Changes in ocean

circulation or seawater properties can disrupt this hydrological cycle

on a global scale, affecting the frequency and intensity of floods and

long-term droughts in various regions. The El Niño phenomenon is

but one example of how oceanic changes can dramatically affect

where and how much precipitation falls throughout the planet.

Thus, the oceans and the atmosphere constitute intertwined

components of Earth’s climate system. Unfortunately, our knowledge of ocean dynamics does not match our knowledge of atmospheric processes. The oceans’ essential role is too often neglected in

our calculations. 

An ‘Achilles’ Heel’ in the Climate System

Here is a simplified description of some basic ocean-atmosphere

dynamics that regulate Earth’s climate: The equatorial sun warms the

ocean surface in the tropics. That enhances evaporation, sending

water vapor into the atmosphere and leaving behind salt in the

tropical ocean. The Gulf Stream, a surface limb of the Ocean Conveyor,

carries an enormous volume of heat-laden, salty water up the East

Coast of the United States. An extension of the Gulf Stream carries

these relatively warm waters northward toward Greenland, Iceland,

and Europe.

This oceanic heat pump is an important mechanism for reducing equator-to-pole temperature differences. It moderates Earth’s

climate, particularly in the North Atlantic region. At colder northern

latitudes, the ocean releases this heat to the atmosphere—especially in winter when the atmosphere is colder than the ocean and

ocean-atmosphere temperature gradients increase. The Conveyor

warms North Atlantic regions by as much as 5° Celsius and significantly tempers average winter temperatures. 

But records of past climates—from a variety of sources such as

deep-sea sediments and glacial ice cores—show that the Ocean

Conveyor has slowed and shut down several times in the past. This

shutdown curtailed heat delivery to the North Atlantic and caused

substantial cooling throughout the region. As one prominent earth

scientist put it, the Ocean Conveyor may be “the Achilles’ heel of our

climate system.”

5

Turning Off the Ocean Conveyor

What can shut down the Conveyor? Solving this puzzle requires

an understanding of what launches and drives the Conveyor in the

first place. The answer, to a large degree, is salt.

The ocean is far from a homogeneous mass of salty water. Its

composition varies greatly. Vast ocean currents, both on the surface

and at depth, circulate various types of water masses on a global scale.

For a variety of reasons, North Atlantic waters are relatively

salty compared with other parts of the world ocean. Salty water is

denser than fresh water. Cold water is denser than warm water.

When the relatively warm, salty waters of the North Atlantic release

heat to the atmosphere, they become colder and denser, and begin

to sink. (Fig. 1a and Fig. 1b)

In the seas that ring the northern fringe of the Atlantic—the

Labrador, Irminger, and Greenland Seas—the ocean releases large

amounts of heat to the atmosphere and then a great volume of cold,

salty water sinks to the abyss. This water flows slowly southward, far

beneath the Gulf Stream, into the South Atlantic and eventually

throughout the world’s oceans. 

Thus, the North Atlantic is a primary source of the deep limb of

the Ocean Conveyor. The plunge of this great mass of cold, salty water

helps drive the global ocean’s conveyor-like circulation system. It also

helps draw warm, salty tropical surface waters northward to replace

the sinking waters. This process is called “thermohaline circulation,”

from the Greek words “thermos” (heat) and “halos” (salt).

If cold, salty North Atlantic waters did not sink, a primary force

driving global ocean circulation could slacken and cease. Existing

currents could weaken or be redirected. The resulting reorganization

of the ocean’s circulation would reconfigure Earth’s climate patterns. 

Computer models simulating ocean-atmosphere climate

dynamics indicate that the North Atlantic region would cool several

degrees if Conveyor circulation were totally disrupted.6 In addition,

these North Atlantic cooling events have been correlated with more

distant regional climate shifts, including disruptive changes in the

2 Defense Horizons October 2003
Figure 1b. Shutting Down the Ocean Conveyor

If too much fresh water enters the North Atlantic, its waters could stop

sinking. In such a scenario, warm Gulf Stream waters (dark lines) would no

longer flow into the northern North Atlantic to release heat to the atmosphere. As a result, European and eastern North American winters would

become more severe.

South Asian monsoon, whose rains are probably the most critical factor supporting populations from Africa to India to China.7

It is crucial to remember several points: 

■ If thermohaline circulation shuts down and induces a climate transition, severe winters in the North Atlantic region may persist for decades—

until conditions reached another threshold at which thermohaline circulation might resume.

■ Abrupt regional cooling may occur even as the earth, on average,

continues to warm. Thus, policymakers might be planning for climate scenarios of global warming that are opposite to what might actually occur in

some regions.

■ The timing of any Conveyor slowdown is critical: If one occurred

within the next two decades, for example, the North Atlantic region could

quickly and markedly cool. But if the Conveyor slowed a century from now,

cooling of the North Atlantic region might partially or totally offset the accumulated impacts of gradual global warming. In the latter scenario, the climate of the economically developed North Atlantic region might rapidly

return to one that more resembles today’s—even as other parts of the world,

particularly less-developed regions, experience the unmitigated brunt of

global warming.8

Worrisome Signals in the Ocean

If the climate system’s Achilles’ heel is the Conveyor, the Conveyor’s vulnerable spot is the North Atlantic. An influx of fresh water

into the North Atlantic’s surface could create a lid of fresh water,

which is more buoyant and lies atop denser, saltier water. This fresh

water would effectively cap and insulate the surface of the North

Atlantic, curtailing the ocean’s transfer of heat to the atmosphere.

An influx of fresh water would also dilute the North Atlantic’s

salinity. At a critical but unknown threshold, when North Atlantic

waters are no longer sufficiently salty and dense, they may stop sinking. An important force driving the Conveyor could quickly diminish,

with climate impacts resulting within a decade.

In an important paper published in 2002 in Nature, oceanographers monitoring and analyzing conditions in the North Atlantic concluded that the North Atlantic has been freshening dramatically—

continuously for the past 40 years, but especially in the past decade.9

The new data show that since the mid-1960s, the subpolar seas feeding the North Atlantic have steadily and noticeably become less salty

to depths of 1,000 to 4,000 meters. The Nature article authors

described the finding as the largest and most dramatic oceanic

change ever measured in the era of modern instruments.

To date, the influx of fresher water has been mixed and distributed into the ocean. But at some point, fresh water may accumulate

sufficiently in the North Atlantic to slow down or halt the Conveyor.

Signs of a possible slowdown already exist. A 2001 report in

Nature indicates that the flow of cold, dense water from the Norwegian and Greenland Seas into the North Atlantic has diminished by

at least 20 percent since 1950.10

Another Vulnerable Spot—the Arctic Ocean

It is generally believed that the Arctic Ocean is the canary in

the coalmine of the climate system. The interactions among the Arctic region’s air, sea ice, and underlying ocean circulation constitute

a sensitive system that is susceptible to disruptions. These disruptions can themselves trigger further and farther ocean circulation

and climate changes. Here is a simplified description of some basic

Arctic Ocean dynamics:

Waters flow into and out of the largely enclosed, ice-covered Arctic Ocean through four gateways. These gateways regulate a delicate

balance between relatively fresh and salty waters in the Arctic Ocean. 

Pacific waters enter in the western Arctic through the Bering

Sea gateway. Warmer, saltier waters—originating from the

Atlantic—enter the Arctic through three other gateways: the Fram

Strait, the Barents Sea, and Baffin Bay. Through these latter three

gateways, cold Arctic waters also exit into the North Atlantic, where

they contribute to the sinking mass of cold waters that helps propel

October 2003 Defense Horizons 3

Figure 1a. The North Atlantic Ocean-Atmosphere System

Today

The Ocean Conveyor is driven by the sinking of cold, salty (and therefore

denser) waters in the North Atlantic Ocean (white lines). Warm surface

currents (dark lines) give up heat to the atmosphere above the North

Atlantic, and prevailing winds (large arrows) carry the heat eastward to

warm Europe.

Source: E. Paul Oberlander/WHO1 Graphics Services. Source: E. Paul Oberlander/WHO1 Graphics Services.
the Conveyor. Added to this delicately balanced mix is fresh water

from melting glaciers and sea ice, and from the drainage of many

large rivers in Canada and Eurasia.

In the Arctic Ocean Basin, cold air temperatures freeze seawater into sea ice. This releases salt into surface waters, which become

denser and sink. The process creates a thin layer of sea ice and fresh

water at the surface—above a layer of denser, saltier waters, known

as a halocline. (Fig. 2)

The halocline provides a barrier to mixing that would otherwise

bring deeper, warmer waters in contact with the sea ice cover. The

heat content of this deeper water is sufficient to melt the ice from

below, adding an influx of fresh water that could flood the North

Atlantic and disrupt the Conveyor.

Additional fresh water may already be entering the Arctic Ocean.

There is some evidence that the volume of Arctic sea ice has

decreased over the past few decades because of increased melting.11 In

addition, the average annual discharge of fresh water to the Arctic

Ocean from the six largest Eurasian rivers has increased by 7 percent

since 1936, according to a study published in Science in 2002.12

These signals point to global warming as a destabilizing factor.

It may increase direct melting of sea ice and glaciers, and it also may

be accelerating the cycle by which water evaporates and precipitates

on Earth’s surface. 

Altering Earth’s Global Water Cycle

About 86% of evaporation on Earth occurs above the oceans and

about 78% of precipitation falls onto the ocean surface. This continual exchange of fresh water between the oceans and atmosphere

influences where and when droughts, floods, and storms occur on

Earth. A warmer Earth could significantly alter this global hydrological cycle, causing tremendous, long-term consequences for society. 

New data, scheduled to be published in 2003, report evidence

that the global hydrological cycle may be accelerating. Over the same

40 years in which the North Atlantic has become fresher, the data

show that the tropical Atlantic Ocean has become steadily saltier.

13

Earth’s warming surface may be intensifying evaporation from tropical and subtropical oceans, concentrating salt in these oceans. 

A warmer atmosphere can hold more water vapor. That, in

itself, could exacerbate greenhouse warming, because water vapor

itself is the most abundant, and often overlooked, greenhouse gas. 

A warmer atmosphere holding more water vapor could also

accelerate the atmospheric transport of fresh water from tropical

regions to higher latitudes. There, it falls into the oceans as rain,

diluting ocean salinity and increasing the likelihood of an Ocean

Conveyor shutdown.

Critical Thresholds

At what salinity threshold will the Ocean Conveyor cease? What

are the ocean mixing and circulation processes that create, maintain, and threaten the Arctic halocline? 

The short answer to both these questions is: We do not know. 

Though we have invested in, and now rely on, a global network

of meteorological stations to monitor fast-changing atmospheric conditions, we do not have a system in place for monitoring slowerdeveloping, but critical, ocean circulation changes. 

Historically, most oceanographic measurements were taken by

research ships and ships of opportunity for anti-submarine warfare

purposes, especially during the Cold War. Many were taken incidentally by Ocean Weather Stations (OWS), a network of ships stationed

in the ocean after World War II, whose primary duty was to guide

transoceanic airplane flights. Starting in the 1970s, satellite technology superseded these weather ships. The demise of the OWS network and the end of the Cold War have left oceanographers with

access to far less data in recent years.

Initial efforts to remedy this deficit are under way, but these

efforts are nascent, and time is of the essence. Satellites can measure wind stress, sea surface temperatures, ocean color, and ocean

circulation globally, but they can observe only the ocean’s surface,

not the crucial processes occurring in the ocean’s interior.

Also, recently launched (but not nearly fully funded) is the

Argo program—an international program to seed the global ocean

with an armada of some 3,000 free-floating buoys that measure

upper ocean temperature and salinity. Measuring deep ocean currents is critical for observing Ocean Conveyor behavior, but it is more

difficult. Efforts have only just begun to measure deep ocean water

properties and currents at strategic locations with long-term,

moored buoy arrays. Vast ocean voids remain unmonitored. 

Ocean salinity changes that affect the hydrological cycle, ocean

circulation, and climate also have not been adequately monitored.

New instruments, such as salinity drifters, are being developed to

take these critical measurements, but they have not been deployed

in any appreciable numbers. 

The Past Predicts the Future

Revealing the past behavior of Earth’s climate system provides

powerful insight into what it may do in the future. Geological records

confirm the potential for abrupt thermohaline-induced climate transitions that would generate severe winters in the North Atlantic region. 

4 Defense Horizons October 2003

Figure 2. The Arctic Halocline

Arctic air temperatures freeze seawater into sea ice. Salt is rejected,

creating denser waters that sink. The process creates a thin layer of sea ice

and fresh water at the surface, above a layer of denser, saltier waters,

called a halocline. The delicately balanced halocline provides a barrier to

mixing that would otherwise bring deeper, warmer waters in contact with

the sea ice cover. The heat content of this deeper water is sufficient to

melt the ice from below.

Source: Jack Cook/WHO1 Graphics Services.
About 12,700 years ago, as Earth emerged from the most recent

ice age and began to warm, the Ocean Conveyor was disrupted.

Within a decade, average temperatures in the North Atlantic region

plummeted nearly 10° Celsius. 

This cold period, known as the Younger Dryas, lasted 1,300

years. It is named after an Arctic wildflower. Scientists have found

substantial evidence that cold-loving dryas plants thrived during

this era in European and US regions that today are too warm to sustain dryas. Deep-sea sediment cores show that icebergs extended as

far south as the coast of Portugal. The Younger Dryas ended as

abruptly as it began. Within a decade, North Atlantic waters and the

regional climate warmed again to pre-Younger Dryas levels.

A similar abrupt cooling occurred 8,200 years ago.14 Average

temperatures spanning from Canada and the eastern US to Europe

and Alaska dropped about 5° C. Drier and windier conditions prevailed, and regions spanning from North America to Asia and Africa

experienced widespread droughts. This cold, dry period lasted only

about a century—a blip in geological time, but a catastrophe if such

a cooling occurred today. The cause of this so-called 8,200-year event

appears to have been a rapid influx of fresh water into the North

Atlantic, caused by a breach in a large inland lake. 

‘Little Ice Ages’ and ‘Mega-Droughts’

Scientists are investigating whether changes in ocean circulation may have played a role in causing or amplifying the Medieval

Warm Period, when, starting about 1,000 years ago, average winter

temperatures in the North Atlantic region abruptly warmed by a

degree or two. That was warm enough to allow the Norse to establish

settlements in Greenland. 

Then, starting in about 1350 A.D., the climate of the North

Atlantic region turned abruptly colder, until about 1850. This period,

known as the “Little Ice Age,” was characterized by abruptly shifting

climate regimes and more severe winters. It had profound agricultural, economic, and political impacts in Europe and North America

and changed the course of history. 

During this era, the Norse abruptly abandoned their settlements

in Greenland. The era is captured in Leutze’s painting of Washington

crossing the frozen Delaware and in the frozen European landscapes

of Pieter Bruegel’s 16th-century paintings. But the era is also marked

by persistent crop failures, famine, disease, and mass migrations.

“The Little Ice Age,” wrote Brian Fagan, Professor of Archaeology at

the University of California at Santa Barbara, “is a chronicle of human

vulnerability in the face of sudden climate change.”

15

A bad winter or two brings inconvenience that societies can

adapt to with small, temporary adjustments. But a persistent string

of severe winters, lasting a decade or more, can cause glaciers to

advance, rivers and harbors to freeze, and sea ice to grow and spread,

as well as agricultural disruptions. 

Societies are similarly vulnerable to abrupt climate changes

that can turn a year or two of diminished rainfall into prolonged,

severe, widespread droughts. A growing body of evidence from joint

archaeological and paleoclimatological studies is demonstrating that

abrupt climate shifts may be linked to “mega-droughts” that precipitated collapses of civilizations—including the Akkadian empire in

Mesopotamia 4,200 years ago, the Mayan empire in Central America

1,100 years ago,16 and the Anasazi in the American Southwest in the

late 13th century.17

Planning for Potential Climate Change 

How have governmental agencies responded to the potential

for climate change? In recent years, the Department of Defense, the

US Army Corps of Engineers, the Environmental Protection Agency,

and other agencies have acknowledged that climate change does

pose potential problems.18 But these agencies have largely focused

on gradual warming forced by atmospheric change. 

The EPA’s Web site on climate change, for example, says that

“Increasing concentrations of greenhouse gases are likely to accelerate the rate of climate change,” and lists several impacts, including

warmer global surface temperatures, increased evaporation and precipitation, declining soil moisture, more frequent storms, and rising

sea levels.19

“Global warming poses real risks,” but “the exact nature of

these risks remains uncertain,” the EPA site reads. “These uncertainties will be with us for some time, perhaps decades. Ultimately,

this is why we have to use our best judgment—guided by the current

state of science—to determine what the most appropriate response

to global warming should be.”

Similarly, the prevailing US military attitude is that a wealthy

superpower has ample time and resources to adapt to gradual and

anticipated climate change. In the meantime, the primary US military strategies on climate change involve publicized efforts to reduce

greenhouse gas emissions and fuel consumption. They foresee few, if

any, climate-induced security threats.20

Direct and Indirect Military Impacts

Environmental changes, however, can precipitate security

threats. A widely cited paper by Richard Ullman of Princeton University, “Redefining Security,” defines a natural security threat as

anything that can quickly degrade the quality of life of the inhabitants of a state or narrow the choices available to people and organizations within the state.21 The two principal criteria for determining

an environmental security issue, therefore, are a short onset period

and a serious impact. 

These are precisely what an abrupt climate change can bring—

rapid changes that can have large, detrimental impacts on agriculture, water resources, energy resources, fisheries, transportation,

economic activities, disaster relief, and public health (associated

with climate-related, vector-borne diseases, such as malaria and

cholera, for example).

Societies can adapt more easily to gradual, anticipated changes

than they can to rapid, unforeseen ones. Developing countries, in particular, which lack scientific resources and economic infrastructures,

are especially vulnerable to the social and economic upheavals caused

by abrupt climate change. But with growing globalization of

economies, adverse impacts (although likely to vary from region to

region) are likely to spill across national boundaries, through human

and biotic migration, economic shocks, and political aftershocks, the

NAS Abrupt Climate Change report said.

October 2003 Defense Horizons 5
It does not take a lot of imagination, for example, to envision

how deleterious changes in the monsoons in South Asia (which

encompasses half the world’s population and several nuclear-armed

nations) could quickly escalate into security threats for the United

States; or how an abrupt cooling in the North Atlantic region could

lead to consecutive severe winters that tax the energy resources and

economies of the US and Europe—quickly degrading inhabitants’

quality of life and narrowing the choices available to them.

Beyond environmental threats that could lead to war, however,

abrupt climate changes could pose more specific consequences to

the US military. If they occur in a 3-to-10-year timeframe, the military, without prior planning, could be in a poor position to respond in

timely fashion.

Given our current state of knowledge, we cannot predict the

probability of any abrupt climate change. But since the possibility is

real, it seems a useful exercise to contemplate the military ramifications of potential, abrupt climate changes. Many of these stem from

potential changes in the North Atlantic and Arctic Oceans. As previously noted, changes within each of these ocean basins may be interrelated and simultaneous, but let us consider each separately. 

Changes in North Atlantic Ocean Circulation

In this scenario, the sinking of cold, salty North Atlantic

waters is curtailed. The effects are two-fold: they could change the

temperature and salinity structure of the water column, and they

could lead to dramatic climate changes. Here are a few potential

military impacts:

Acoustic propagation pathways. A significantly different water

column structure could have dramatic effects on present-day

acoustic propagation pathways in the ocean. These acoustic paths,

discovered in the late 1940s, formed the basis for all of the US and

allied Anti-Submarine Warfare (ASW) Sensor Systems and aided significantly in winning the ASW battle of the Cold War.22 A rapidly

changed ocean environment could invalidate existing acoustic prediction systems, which use historic climatology to calculate acoustic

paths, propagation loss, bottom loss, and ambient noise. 

An Ocean Conveyor shutdown, for example, could lead to

windier conditions in the North Atlantic, which would increase ambient noise and force major adjustment in existing prediction systems.

The existing deep sound channel could disappear, decreasing the

performance of fixed acoustic surveillance systems. North Atlantic

acoustic conditions may change to more closely resemble presentday pathways in the Norwegian Sea, which, in general, are characterized by half channel propagation, rather than by a deep sound

channel and surface duct conditions.

Different acoustic propagation pathways would demand adjustments on all tactical platform (air, sub, surface) sensors. The

changed acoustic propagation regimes would be exploitable but

would require reengineering, redesign, or even relocation of systems. 

Ocean environmental now-casts and forecasts. The Navy relies

on good environmental data and prediction for strategic planning

and everyday operations. They are a critical element of effective

operations.23 Currently, the Navy creates ocean environmental nowcasts and forecasts of sea and wave heights and directions, marine

and aviation weather, ocean current fronts and eddies, and long- and

short-range acoustic propagation, for example. All of these products

use existing models and historic climatology as their backgrounds.

All would be impacted (some severely), should the climatology be

invalidated by abrupt climate change. 

A stormier Atlantic Ocean. A colder, stormier North Atlantic

would change the Navy’s ability to operate in the region. It would

increase the hazard (storm damage) of operating in this strategically vital region. It would reduce the Navy’s access to the shortest

(great circle) routes between US East Coast ports and Europe. 

Frozen harbors. If North Atlantic conditions lead to consistently

cooler winters on the US East Coast, it could result in freezing harbors,

particularly at Norfolk, VA, a major American strategic naval base.

Norfolk is the largest operating base of aircraft carriers and

their contingents of subs, destroyers, and auxiliary support ships.

The Norfolk area complex is also a major supply center, shipyard,

and naval air station, where training for carrier planes takes place.

Alternative ports in Charleston and Florida exist, but these have

questionable capacity to handle all Norfolk ships, particularly the

aircraft carriers. 

The severe winter of 1976-77 provides a picture of what could

be the norm if the North Atlantic region abruptly cools.24 The waters

around Norfolk, including the Chesapeake Bay and Elizabeth and

Yorktown Rivers froze solid. When this ice moved, it displaced or

ripped out navigation aids. Navigation on the Chesapeake and Yorktown Rivers became treacherous and was shut down or curtailed on

these important waterways for significant periods of time. Ships

were trapped in and out of port. Considerable expense was required

to use tugs to clear harbors.

An abrupt climate change, producing several decades of severe

winters, could have considerable impact on Navy ports, including the

US Submarine Base in Groton, CT, as well as on all the important

commercial ports on the Northeast Coast (Boston, Philadelphia,

New York, Baltimore).

Cold-weather operations. During the recent, post-Cold War era,

military planners have been heavily influenced by the wars in Iraq

and Afghanistan and have focused on fighting in dry, dusty, warm and

hot conditions. Even the series of conflicts in the former Yugoslavia

found the US Navy operating in the reasonably temperate Mediterranean Sea. As a consequence, emphasis on cold-weather operations

has waned across all the services. 

A colder region spanning eastern North America, Europe, and

Russia would require all branches of the military to review that trend

and equip and train forces to operate in cold-weather environments. 

Naval Operations Beyond the North Atlantic

Changes in North Atlantic Ocean circulation conceivably could

lead to more distant effects in other oceans, with important ramifications for naval operations. Along the strategic Arabian coast, for example, Robert Weller, a senior scientist at Woods Hole Oceanographic

Institution, has pointed out peculiar ocean-atmosphere dynamics that

create narrow flows of very cool water, or jets, that extend offshore.25

They affect the lower atmosphere—changing wind speeds, air temperature, humidity, and optical and electromagnetic propagation.

6 Defense Horizons October 2003
“An aircraft carrier battle group steaming into the southwest

monsoon winds to recover aircraft should anticipate changes in wind

speed and atmospheric turbulence as it crosses the jets” and should

anticipate being “vulnerable to quiet submarines using the environmental variability of the cool jets to screen their approach,” Weller

said. “The carrier and screening ships should expect changes in

radar, IR, and optical propagation in the air and in optical and

acoustic propagation in the ocean.”

Cold periods in the North Atlantic region appear to be coincident with milder monsoonal conditions in the Indian Ocean/Arabian

Gulf region. An abrupt climate shift could shift monsoonal winds patterns and intensities; naval personnel would have to discover these

changes and learn how to compensate for them.

An Ice-Free or Navigable Arctic Ocean. Several recent indications that the Arctic ice cap may be thinning has led to considerable

discussion of the implications of a more ice-free, navigable Arctic

Ocean. But this discussion has failed to consider a critical point:

Large-scale Arctic Ocean changes could occur much sooner and

more precipitously—if the changes are caused by changes in ocean

circulation or properties—a breach in the halocline, for example—

rather than by more gradual atmospheric warming. 

Naval operations in an open Arctic Ocean. The melting of Arctic sea ice would turn it into a conventional open-ocean ASW environment, with none of the advantages it now affords to an adversary

strategic submarine, according to the report of an April 2001 symposium (“Naval Operations in an Ice-Free Arctic”) hosted by the Office

of Naval Research, the Naval Ice Center, the Oceanographer of the

Navy, and the Arctic Research Commission.26 The disappearance of

the ice canopy will also eliminate the haven now provided to stationary submarines by ice keels. Active sonar detection of submarines, both by ASW sonars, and by acoustic torpedoes, would

become feasible. Though strategic submarines would be more vulnerable in an ice-free Arctic, the ocean would remain a geographically strategic location for such forces. The absence of sea ice would

render the ocean more accessible and viable for any submarine

force—ice-strengthened or not, nuclear or conventional.

Changing acoustics in an open Arctic Ocean. The melting of

Arctic sea ice could expose the sea surface to winds, which could significantly change both ambient noise and acoustic propagation,

according to the Ice-Free Arctic Symposium report. Wind-generated

waves would increase ambient noise in the central Arctic, so that it

more closely resembled a temperate ocean. Wind-generated mixing

of near surface water, combined with warmer air temperatures,

would diminish or eliminate the surface duct, increasing low-frequency propagation loss.

Shorter Arctic maritime routes. For centuries, the quest for safe

routes across the shorter “roof of the earth” have been sought, but ice

conditions have always rendered these shortcuts impassable except

to the most robust icebreaking ships. A navigable Arctic would cut the

distance over the Panama Canal sea route from 12,600 miles to 7,900

miles (a savings of 12 to 15 days in transit time). For ships too large

for the Panama Canal, the distance (via the route around Africa)

would be reduced by 6,770 miles, or 15 to 20 days. A navigable Arctic

Ocean would give the United States the strategic mobility option of

deploying forces, such as carrier battle groups, between theaters

much more rapidly in response to national needs and tasking.

But there are also challenges associated with easier access to

Arctic sea routes.27 Easy access to both the Northwest Passage

(through the Canadian Archipelago) and the Northeast Sea Route

(across the top of Russia) will assuredly invoke major legal issues

with both Canada and Russia under the United Nations Law of the

Seas. Easier access to the Arctic also invites other nations, including

their militaries, to ply these seas. That would present the US with

another coast to defend and necessitate devoting or creating forces

capable of safe and effective operations there.28

A need for more ice-capable ships. Though the Arctic Ocean’s

ice-covered surface may become sufficiently ice-free to encourage

more ship traffic, few are suggesting that it will become completely

ice-free. Thus, more, not fewer, ice-capable ships would be required. 

Since the end of the Cold War, the U.S. Navy has lost a great

deal of its high-latitude capabilities and is no longer well equipped

for high-latitude operations. Most Arctic-capable submarines,

including all the SSN 637 class, have been decommissioned since the

Cold War. Only a few Los Angeles class (SSN 751) subs were built

with limited ice capabilities. Post-Cold War attack submarines of the

SSN 21 and Virginia classes, as well as the ballistic missile submarines, are not ice-capable.29

Surface ships (destroyers, cruisers, replenishment ships,

amphibious ships) are not built to operate in ice. By ice-capable

ship standards, they have thin hulls and are vulnerable to damage

even by thin ice. Aircraft carriers probably could withstand some inice-operations.

Designing and building ice-capable warships is not a trivial,

inexpensive, or speedy enterprise.

Current Naval Shortfalls for Arctic Operations

Projections of capability shortfalls for naval surface forces in

a navigable Arctic Ocean were identified by the Ice-Free Arctic

Symposium report. Key shortfalls in the current Navy program

(POM 02/PR 03) included:

■ Inadequate charts of the Arctic region

■ Navigation training

■ Electronic navigation systems

■ Sensor/Weapon/Communications performance testing

■ Environmental monitoring and modeling (e.g. real-time system performance prediction)

■ Extreme cold weather design/modifications to existing and planned

sensors and weapon systems

■ Hull design and performance/stability monitoring systems

■ Arctic capable damage control systems

■ Ice-clearing systems for phased array radars

■ Icebreakers

■ War gaming in an Arctic scenario

Another indication of the low priority the Department of

Defense places on Arctic issues is the status of Office of Naval

Research (ONR) support for high-latitude research. ONR Arctic

research funding has dropped from about $30M/year to about

$3M/year.30 Other sections of the Navy (Spawar, submarine force and

October 2003 Defense Horizons 7
naval aviation) have all but dropped out of the Arctic research/Arctic operations picture. Virtually the entire Navy Cold War Arctic

infrastructure no longer exists, and the expertise of Navy-supported

researchers is atrophying.

Conclusions 

The debate on global change has largely failed to factor in the

inherently chaotic, sensitively balanced, and threshold-laden nature

of Earth’s climate system and the increased likelihood of abrupt climate change. Beyond our current speculations about future global

warming, it is prudent to superimpose the potential for abrupt climate change induced by ocean and atmosphere circulation changes. 

The key is to reduce our uncertainty about future climate

change, and to improve our ability to predict what could happen and

when. A first step is to establish the oceanic equivalent of our landbased meteorological instrument network. Such a network would

begin to reveal oceanic processes that influence climate and that

have been beyond our ability to grasp. These instruments, monitoring critical present-day conditions, can be coupled with enhanced

computer modeling, which can project how Earth’s climate system

may react in the future. Considerably more research is also required

to learn more about the complex ocean-atmosphere processes that

induced rapid climate changes in the past, and thus how our climate

system may behave in the future.

Most signs, however, indicate that military planners are going

in the opposite direction, assigning research and planning on climate change a low priority. That is a gamble. The challenge to military leaders is to reduce vulnerabilities by enhancing our ability to

monitor, plan for, and adapt to rapid change. Ignoring or downplaying the probability of abrupt climate change could prove costly. Some

current policies and planning—or lack thereof—may be ill-advised

and may prove inadequate in a world of rapid and unforeseen climate change. 

Notes1 Donald Kennedy, “The Climate Divide,” Science 299 (March 21, 2003). 2 David McCullough, John Adams (New York: Simon & Schuster, 2001). 3 U.S. National Academy of Sciences, National Research Council Committee on

Abrupt Climate Change, Abrupt Climate Change: Inevitable Surprises (Washington,

DC: National Academy Press, 2002). 4 T. Joyce and L. Keigwin, “Are We on the Brink of a New Little Ice Age?” Testimony before the U.S. Commission on Ocean Policy, September 25, 2002. 5 W.S. Broecker, “Thermohaline Circulation, the Achilles’ Heel of Our Climate

System: Will Man-Made CO2 Upset the Current Balance?” Science 278 (November 28,

1997). 6 M. Vellinga and R. Wood, “Global Climatic Impacts of a Collapse of the Atlantic

Thermohaline Circulation,” Hadley Centre Technical Note 26, February 2001. 7 Y.J. Yang et al., “A High-Resolution Absolute-Dated Late Pleistocene Monsoon

Record from Hulu Cave, China,” Science 294 (December 14, 2001); D.M. Anderson, J.

Overpeck, and A.K. Gupta, “Increase in the Asian Southwest Monsoon During the Past

Four Centuries,” Science 297 (July 26, 2002). 8 R. Gagosian, “Abrupt Climate Change: Should We Be Worried?” White paper

prepared for the Word Economic Forum, January 27, 2003. 9 B. Dickson et al., “Rapid Freshening of the Deep North Atlantic Ocean Over

the Past Four Decades,” Nature 416 (April 25, 2002). 10 B. Hansen, W.R. Turrell, and S. Østerhus, “Decreasing Overflow from the

Nordic Seas into the Atlantic Ocean through the Faroe Bank Channel Since 1950,”

Nature, 411 (June 21, 2001).

11 P. Wadhams and N. Davis, “Further Evidence of Ice Thinning in the Arctic

Ocean,” Geophysical Research Letters 27, no. 24 (December 15, 2000); J.C. Comiso, “A

Rapidly Declining Perennial Sea Ice Cover in the Arctic,” Geophysical Research Letters 29, no. 20 (October 18, 2002)

12 B.J. Peterson et al., “Increasing River Discharge to the Arctic Ocean,” Science

298 (December 13, 2002). 13 R. Dickson, R. Curry, and I. Yashayaev, “Recent Changes in the North Atlantic,”

in Proceedings from the Royal Society Meeting on Abrupt Climate Change: Evidence,

Mechanisms and Implications (London: Phil. Trans. A., forthcoming 2003). 14 R.B. Alley et al., “Holocene Climate Instability: A Prominent, Widespread

Event 8,200 Years Ago,” Geology 25, no. 6 (1997). 15 Brian Fagan, The Little Ice Age: How Climate Made History 1300-1850 (Santa

Barbara: Basic Books, 2000). 16 G.H. Haug et al., “Climate and the Collapse of Maya Civilization,” Science 299

(March 14, 2003). 17 P.B. deMenocal, “Cultural Responses to Climate Change During the Late

Holocene,” Science 292 (April 27, 2001). 18 U.S. Air Force Center for Environmental Excellence, “Global Warming-Fact

Sheet,” accessed at http://www.afcee.brooks.af.mil/pro-act/fact/oct02.asp; U.S. Environmental Protection Agency, “Global Warming-Climate,” accessed at http://yosemite.

epa.gov/oar/globalwarming.nsf/content/climate.html; LTC P. Greene, USA, “Military

Implications of Global Warming,” in USAWC Strategy Research Project, U.S. Army War

College, May 1999. 19 U.S. Environmental Protection Agency

20 M. Levy, “Is the Environment a National Security Issue?” International Security 20, no. 2 (Fall 1995).

21 R. Ullman, “Redefining Security,” International Security 8, no. 1 (1983); J.

Barnett and S. Dovers, “Environmental Security, Sustainability and Policy,” Pacifica

Review: Peace, Security & Global Change 13, no. 2 (June 2001). 22 O.R. Cote, Jr., “The Third Battle,” Naval War College Newport Papers, no. 16

(March 2003); M. Ewing and L. Worzel, “Long Range Sound Transmission,” Geological

Society of America, Memoir 27 (October 15, 1948); Thaddeus Bell, Probing the Ocean

For Submarines: A History of the AN/SQS-26 Long-Range, Echo-Ranging Sonar,

Department of Defense, NAVSEA, Newport, Undersea Warfare Center Division, March

2003. 23 “Environmental Information for Naval Warfare,” Report by the Ocean Studies

Board of the National Research Council (Washington, DC: National Academies Press,

March 2003). 24 R. Pittenger, personal observation.

25 R. Weller, personal communication.

26 “Naval Operations in an Ice-free Arctic,” Final Report, Office of Naval

Research, Naval Ice Center, Oceanographer of the Navy, and the Arctic Research Commission (Symposium, April 17-18, 2001). 27 D.B. Hill, “Force Projection, Strategic Agility and the Big Meltdown,” Technical Report, U.S. Naval War College, May 18, 2001. 28 J. Bagole, “Northern Thaw Raises Defense Concerns: A Canadian Waterway

Free of Ice May Bring Commerce--and Foes,” The Wall Street Journal, December 20,

2000. 29 L. Keigwin, “Using a Nuclear Submarine for Arctic Research,” in EOS 73, no. 19

(May 12, 1992). 30 George B. Newton, Report to the U.S. Commission on Ocean Policy, August 22,

2002.

8 Defense Horizons October 2003

Defense Horizons is published by the Center for Technology and National Security Policy through the

Publication Directorate of the Institute for National Strategic Studies, National Defense University.

Defense Horizons and other National Defense University publications are available online at

http://www.ndu.edu/inss/press/nduphp.html.

The opinions, conclusions, and recommendations expressed or implied within are those of the

contributors and do not necessarily reflect the views of the Department of Defense or any other

department or agency of the Federal Government.

Center for Technology and National Security Policy

Hans Binnendijk

Director