US National INtelligence Estimate: Climate change and international response

Climate Change and International
Responses Increasing Challenges to
US National Security Through 2040
NIC-NIE-2021-10030-A

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Key Judgment 1: Geopolitical tensions are likely to grow as countries increasingly argue about how to accelerate the
reductions in net greenhouse gas emissions that will be needed to meet the Paris Agreement goals. Debate will
center on who bears more responsibility to act and to pay—and how quickly—and countries will compete to
control resources and dominate new technologies needed for the clean energy transition. Most countries will face
difficult economic choices and probably will count on technological breakthroughs to rapidly reduce their net
emissions later. China and India will play critical roles in determining the trajectory of temperature rise.
Key Judgment 2: The increasing physical effects of climate change are likely to exacerbate cross-border geopolitical
flashpoints as states take steps to secure their interests. The reduction in sea ice already is amplifying strategic
competition in the Arctic over access to its natural resources. Elsewhere, as temperatures rise and more extreme effects
manifest, there is a growing risk of conflict over water and migration, particularly after 2030, and an increasing chance
that countries will unilaterally test and deploy large-scale solar geoengineering—creating a new area of disputes.
Key Judgment 3: Scientific forecasts indicate that intensifying physical effects of climate change out to 2040 and beyond
will be most acutely felt in developing countries, which we assess are also the least able to adapt to such changes.
These physical effects will increase the potential for instability and possibly internal conflict in these countries, in
some cases creating additional demands on US diplomatic, economic, humanitarian, and military resources. Despite
geographic and financial resource advantages, the United States and partners face costly challenges that will become more
difficult to manage without concerted effort to reduce emissions and cap warming.
Key Takeaway
We assess that climate change will increasingly exacerbate risks to US national security interests as the physical
impacts increase and geopolitical tensions mount about how to respond to the challenge. Global momentum is
growing for more ambitious greenhouse gas emissions reductions, but current policies and pledges are insufficient to
meet the Paris Agreement goals. Countries are arguing about who should act sooner and competing to control the
growing clean energy transition. Intensifying physical effects will exacerbate geopolitical flashpoints, particularly
after 2030, and key countries and regions will face increasing risks of instability and need for humanitarian assistance.
• As a baseline, the IC uses the US Federal Scientific community’s high confidence in global projections of
temperature increase and moderate confidence in regional projections of the intensity of extreme weather and
other effects during the next two decades. Global temperatures have increased 1.1˚C since pre-industrial times
and most likely will add 0.4˚C to reach 1.5˚C around 2030.
• The IC has moderate confidence in the pace of decarbonization and low to moderate confidence in how
physical climate impacts will affect US national security interests and the nature of geopolitical conflict, given
the complex dimensions of human and state decisionmaking.
Climate Change and International Responses Increasing
Challenges to US National Security Through 2040

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Scope Note
This National Intelligence Estimate (NIE) is in response to a Presidential tasking to assess the national security
impacts of climate change. While climate change effects are forecast to intensify in the latter half of the 21st
century and continue well beyond 2100, based on current emissions trends and technologies, this NIE assesses the
near- (5–10 years) and medium-term (10–20 years) geopolitical implications abroad—we do not assess impacts to
the homeland or DOD facilities. We assume the following during the next 20 years:
• No precipitating world event that would devastate industrial activity will occur that sharply and permanently
reduces greenhouse gas emissions.
The scientific content of this NIE, both the observed climate effects to date and the modeled future impacts, were
reviewed by the US Federal science agencies on the Climate Security Advisory Council (CSAC). The CSAC is a
partnership between the IC and the Federal science community established by Congress to better understand and
anticipate the ways climate change affects US national security interests. It includes the Environmental Protection
Agency, the Department of Energy, the Department of the Interior/US Geological Survey, the Office of Naval
Research, the National Aeronautics and Space Administration, the National Oceanic and Atmospheric
Administration, and the National Science Foundation.
The IC relies on the broad consensus of scientific studies, modeling, and forecasts from the Intergovernmental Panel
on Climate Change, the US National Climate Assessment, and US Federal science agencies as the baseline to assess
the geopolitical implications of climate change. We are aware of, but in this estimate do not rely on, the small
minority scientific perspectives on climate change ranging from those who consider it nonexistent to those who view
it as a near-term existential threat to humanity.
Confidence Levels
The IC uses as a baseline the US Federal scientific community’s high confidence in global projections of temperature
increase and moderate confidence in regional projections of the intensity of extreme weather and other effects during
the next two decades.
The IC has moderate confidence in the pace of decarbonizing the energy sector, given how historically entrenched and
slow moving energy systems have been to change and the difficulty of predicting technological breakthroughs. Our
confidence decreases after 2030 because government and private sector policies and investments have the potential to
drive a more rapid transition.
The IC has low to moderate confidence in assessing how climate change effects could cascade in ways that affect
US national security interests as well as the timing and location of potential geopolitical tension, given the
complex dimensions of human and state decisionmaking and the challenge of connecting climate, weather, and
sociopolitical models.

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Discussion
Reports from US Federal science agencies and the
Intergovernmental Panel on Climate Change (IPCC)
indicate that the burning of fossil fuels has increased the
concentration of greenhouse gases in the atmosphere and
raised global average surface temperatures about
1.1 degrees Celsius (°C) over pre-industrial levels.
Temperature rise has accelerated, and every decade since
the 1960s has been hotter than the previous one, according
to the National Aeronautics and Space Administration.
International diplomatic efforts since the late 1980s have
centered on understanding and mitigating the effects a
changing climate poses to human security. The 2015
Paris Agreement for the first time established a global
goal of limiting temperature rise to “well below 2˚C
above pre-industrial levels and pursuing efforts to limit
the temperature increase to 1.5˚C” by 2100, concluding
that this would “significantly reduce the risks and impacts
of climate change.” US Government and other scientists
argue that the risks grow as the temperature rises and
could be catastrophic and nonlinear after 2˚C if there are
tipping points in the Earth’s system. (See Annex B.)
• In the Paris Agreement, more than 190 countries
agreed to submit updated plans—known as
Nationally Determined Contributions (NDC)—
every five years that should outline increased
commitments to peak and reduce their emissions.
NDCs are voluntary and have no enforcement
mechanism for non-compliance.
• Developing countries––which have long argued
that they should not have to limit emissions
because they were late in industrializing, need to
use fossil fuels to grow economically, and have
historically emitted fewer greenhouse gases––
signed on to the Paris Agreement in part because it
did not require country-specific emissions
reduction targets. In addition, developed countries
pledged to mobilize $100 billion a year by 2020 to
help developing countries mitigate and adapt to
climate change.
Pressure To Decarbonize Will Increase
Geopolitical Tensions
Key Judgment 1: Geopolitical tensions are likely to
grow as countries increasingly argue about how to
accelerate the reductions in net greenhouse gas
emissions needed to meet Paris Agreement goals.
Debate will center on who bears more responsibility to
act and to pay—and how quickly—and countries will
compete to control resources and dominate new
technologies required for the clean energy transition.
Most countries will face difficult economic choices and
Trajectory of Climate Change
The current trajectory of growing global CO2
emissions would cause global temperatures—at
1.1˚C over pre-industrial levels now—to add 0.4˚C
and cross the 1.5˚C threshold by about 2030,
according to modeling from the National Oceanic
and Atmospheric Administration (NOAA), and
surpass 2˚C by around mid-century. Many of the
physical effects are projected to increase in intensity,
frequency, and speed.
To change that trajectory, the IPCC estimates that
global emissions would have to drop sharply in the
next decade and reach net zero by around 2050 to
limit warming to 1.5˚C, or reach net zero by about
2070 to limit warming to 2˚C.
Climate Change and International Responses Increasing
Challenges to US National Security Through 2040

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probably will count on technological breakthroughs to
rapidly reduce their net emissions later. China and
India will play critical roles in determining the trajectory
of temperature rise.
Policies Not Driving Decarbonization Fast Enough
Given current government policies and trends in
technology development, we judge that collectively
countries are unlikely to meet the Paris goals because
high-emitting countries would have to make rapid
progress toward decarbonizing their energy systems by
transitioning away from fossil fuels within the next
decade, whereas developing countries would need to
rely on low-carbon energy sources for their economic
development. Quickening the pace and trajectory of the
energy transition will depend on reducing key countries’
continued dependence on fossil fuels; investing in
research, development, and deployment of low-carbon
technologies for specific sectors that are hard to
decarbonize; and enacting policies to incentivize
renewable energy sources.
The current pace of transition to low- or zero-emission
clean energy sources is not fast enough to avoid
temperatures rising above the Paris goal of 1.5˚C.
Global energy demand is expected to increase by more
than 18 percent by 2040, according to the International
Energy Agency’s (IEA) modeling of current policies,
with fossil fuel use also growing and continuing to
account for only a modestly smaller share of supply even
though solar, wind, and other clean sources will grow
more quickly, particularly after 2030.
• To achieve the 1.5˚C goal through shifts in energy,
coal use would need to decline, oil use would need
to fall immediately rather than plateau in the 2030s,
and natural gas consumption would have to peak
this decade, according to IEA data and modeling.
• Fossil fuels will be difficult to replace because the
large sunk costs of established production systems
make them competitively priced, existing
distribution networks offer advantages of flexibility
and reach, and scaling alternatives to the level
necessary to replace them is difficult. Industrial
and transportation sectors will struggle to reduce
their reliance on fossil fuels because these sectors
are the most dependent on the high energy density
that fossil fuels provide.
• Solar photovoltaic and wind generation almost
certainly will increase worldwide because they are on
average the cheapest form of energy to add to an
electricity grid in many countries—particularly when
factoring in installation and lifetime operating
expenses. Accelerating the speed and scale of their
deployment would require new manufacturing
capacity, changes to electricity grids and markets, and
development of more advanced batteries to provide
power when there is no sun or wind.
• Nuclear and hydropower are forecast to maintain,
at most, their current modest shares of energy
supply. Some countries are planning to expand

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nuclear power generation, but others plan to reduce
it because of safety concerns and high costs. The
development of small modular nuclear reactors
may lead to renewed expansion; given long lead
times in production, any notable increase in
capacity would occur during the latter part of the
period of this estimate.
World leaders are increasingly concerned that a window
is closing on the opportunity to reduce emissions before
irreversible damage to the climate occurs, and many are
responding to public and global pressure to act more
ambitiously. A growing number of countries are imposing
or increasing carbon taxes to discourage emissions and
increase the cost competitiveness of clean energy sources
and carbon dioxide removal. In addition, private and
public investment in these areas is rapidly increasing.
• By summer 2021 more than 90 countries—covering
more than 40 percent of global emissions—had
submitted updated NDCs. Several had pledged to
reach net zero emissions, including Brazil, Chile, the
EU, Japan, South Korea, New Zealand, and the
United Kingdom by 2050, and China by 2060.
• In March, the European Central Bank announced
plans for new capital requirements for banks that
have high levels of climate risks on their accounts,
and in April, the United Kingdom passed
legislation codifying its emissions target. In July,
the EU unveiled its emissions reduction roadmap.
• However, few other countries have enshrined these
targets into law or have detailed plans on how to get
there. For example, industry analysts estimate a
carbon price as high as $100 per ton would be needed
to accelerate a shift to clean energy. In addition, we
assess that some countries are using a pledge to mask
a lack of seriousness.
Carbon Dioxide Removal Key to Meeting Paris Goals
Most countries are delaying major emissions cuts until closer to their net-zero target year, which means that
breakthroughs, commercialization, and incentives related to carbon dioxide removal (CDR) technologies will
be critically important for meeting their goals. Australia, China, the EU, Japan, the United Kingdom, and the
United States are leading R&D efforts and pilot projects, according to the Global Carbon Capture Sequestration
Institute, but deployment sufficient to meet the goals of the Paris Agreement is contingent on either technological
breakthroughs that sharply reduce costs or government support through subsidies and taxes that raise the costs of
fossil fuels. Currently, there is no large-scale market use for CO2.
• Major hydrocarbon producing countries in Europe, led by Norway and the United Kingdom, probably are
best positioned for large-scale CDR deployment during the next decade because of government policy and
regulatory regimes to support its growth, including carbon-pricing schemes.
• The United States has several advantages that position it to become a leader in CDR. US companies are investing
heavily and have experience using CDR to enhance oil and gas yields. In addition, the United States is home to
almost half the world’s operating carbon capture facilities and has large geologic storage capacity, including
natural gas reservoirs and saline aquifers, according to the US Geological Survey (USGS).
• More countries probably will invest in and tout CDR as key to offsetting their emissions and prolonging fossil
fuel production and consumption. Oil and gas companies are increasing their R&D in CDR for similar reasons.

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China and India will play critical roles in determining
the trajectory of temperature rise. They are the first-
and fourth-largest emitters, respectively, and both are
growing their total and per capita emissions, whereas
the United States and EU—as the second- and third-
largest—are declining. Both China and India are
incorporating more renewable and low-carbon energy
sources, but several factors will limit their displacement
of coal. They need to modernize their grids, have sunk
costs that make it relatively cheaper to use coal
compared with other energy sources, want to minimize
reliance on fuel imports for national security reasons,
and are trying to appease domestic constituencies who
rely on the coal industry for jobs.
• China accounts for about 30 percent of global
emissions and has pledged to peak before 2030,
but modest emissions reduction targets in its
14th Five Year Plan (2021–2025) in 2021 put
that into question. China has not publically
articulated detailed plans for meeting its 2060
net-zero-emissions target; to do so, we assess that
Beijing would need to follow through on
President Xi Jinping’s pledge at the US Climate
Summit in April to phase out coal consumption.
• India almost certainly will increase its emissions as it
develops economically. Indian officials have not
committed to a net-zero target date and have instead
called on countries with larger economies to reduce
emissions.
Arguing About Who Bears Responsibility To Act
The cooperative breakthrough of the Paris Agreement
may be short lived as countries struggle to reduce their
emissions and blame others for not doing enough. The
Paris Agreement allows countries to self-report
emissions data, which means that increased
transparency, monitoring, and consistency in reporting
will be necessary to accurately measure and assess which
countries are meeting their commitments.
• We assess that the longstanding diplomatic divide
between expected contributions from developed
versus developing countries will persist. Most
developing countries almost certainly will continue
to submit conditional targets, arguing that developed
countries must provide substantial financial
assistance—as called for in the Paris Agreement—
technology transfers, and aid in capacity building for
them to reach their NDC goals.
• Developing countries will continue to press for
more money to mitigate and adapt to climate
change, arguing that developed countries’ failure to
mobilize $100 billion a year starting in 2020 has
hampered their ability to take serious action.

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Financial needs will grow as the physical effects
intensify; the UN estimates that developing
countries will need upwards of $300 billion in
annual investment by 2030 just to adapt.
• In addition, countries probably will continue to
present favorable data or compare their reductions
against a chosen baseline year to their benefit.
Russia’s target is baselined to 1990 levels—at the
height of the Soviet Union’s economic activity and
before Russia’s economic collapse in the 1990s—
which allows it to appear ambitious in meeting its
goal. Brazil updated its NDC in 2020 by
recalculating its 2005 baseline number upwards,
allowing it to claim it is still on track to meet its goal.
Growing Competition Over Key Minerals
and Technologies
Competition will grow to acquire and process minerals
and resources used in key renewable energy
technologies. China is in a strong position to compete;
it currently controls more than half the global processing
capacity for many of these minerals, according to the
USGS and industry reporting, including rare earths for
wind turbines and electric vehicle motors; polysilicon for
solar panels; and cobalt, lithium, manganese, and
graphite for electric vehicle batteries. China is able to
process these at reduced cost mainly because of its lower
environmental standards, lower labor costs, and
inexpensive power.
Countries will increasingly compete over developing
renewable energy technologies to become leading
exporters and gain market share as the energy
transition picks up speed. This competition
potentially will enable technological breakthroughs
that could speed up decarbonization.
• The decarbonization of the electricity sector,
combined with the electrification of transportation,
will require countries to upgrade and expand their
grids. Under current policies, the global electric
vehicle stock is projected to grow twentyfold by
2030 and account for 7 percent of the global fleet,
according to the IEA.
• Deployment of utility-scale solar and wind
technologies in remote areas is likely to require
ultra-high-voltage transmission lines to move the
power to cities. China is the world’s leading
supplier of advanced grid components for ultra-
high-voltage systems, such as transformers, circuit
breakers, and inverters, which we assess creates
cyber vulnerability risks.
• Private firms and governments in China, the EU,
Japan, Russia, and the United States are increasing
R&D efforts on emerging energy technologies to

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provide additional zero- to low-carbon options,
such as green hydrogen, floating offshore wind,
and small modular nuclear reactors. The potential
to gain an edge in markets that could be worth
hundreds of billions to trillions of dollars is fueling
increasingly intense competition.
Use of Contentious Economic Tools To Advance
Climate Interests
Countries most likely will wield contentious financial
and economic tools to advance climate policies and
defend their national economies. Some countries are
looking to impose costs on foreign goods produced in
countries with relatively weak carbon reduction
standards to protect domestic producers who are
complying with more stringent standards.
• The EU plans to propose a new Carbon Border
Adjustment Mechanism for implementation as
early as 2023, to protect EU firms in certain sectors
from competing with companies from countries
with weaker climate rules and emissions prices,
according to open-source reporting.
• Australia, China, India, Russia, South Africa, and
Ukraine have criticized the use of such
mechanisms as a disguised form of protectionism.
Climate Change Effects Exacerbating
Geopolitical Flashpoints
Key Judgment 2: The increasing physical effects of
climate change are likely to exacerbate cross-border
geopolitical flashpoints as states take steps to secure
their interests. The reduction in sea ice already is
amplifying strategic competition in the Arctic over
access to its natural resources. Elsewhere, as
temperatures rise and more extreme effects manifest,
there is a growing risk of conflict over water and
migration, particularly after 2030, and an increasing
chance that countries will unilaterally test and deploy
large-scale solar geoengineering—creating a new area of
geopolitical disputes.
Petrostates Fear Transition Risk in International Decarbonization Efforts
We assess that most countries that rely on fossil fuel exports to support their budgets will continue to resist a
quick transition to a zero-carbon world because they fear the economic, political, and geopolitical costs of
doing so. US and Western efforts to push these countries to speed up the energy transition could complicate
bilateral relations and force tradeoffs with other national security priorities.
• Russian President Vladimir Putin only recently acknowledged the economic damage from climate change.
Russia generated almost 30 percent of state revenue in 2020 from fossil fuel companies, including $40 billion
in gas sales to Europe.
• More than 20 countries rely on fossil fuels for greater than 50 percent of total export revenues, and most will
continue to struggle to diversify their sources of export revenue because of entrenched political interests,
endemic corruption, and the lack of economic and legal institutions. Most already face major governance
and instability challenges, with Algeria, Chad, Iraq, and Nigeria most at risk from falling fossil fuel prices
because they have higher break-even prices, according to industry reporting.
• A decline in fossil fuel revenue would further strain Middle Eastern countries that are projected to face more
intense climate effects—such as very high heat and extended droughts—because it will reduce available
resources needed to adapt or build more resilient infrastructure.

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Growing Strategic Competition in the Arctic
We assess that Arctic and non-Arctic states almost
certainly will increase their competitive activities as
the region becomes more accessible because of
warming temperatures and reduced ice. Competition
will be largely economic but the risk of
miscalculation will increase modestly by 2040 as
commercial and military activity grows and
opportunities are more contested.
• Diminishing sea ice probably will increase access to
shipping routes that can reduce trade times
between Europe and Asia by about 40 percent for
some vessels. In addition, onshore oil and natural
gas deposits, as well as an estimated $1 trillion
worth of precious metals and minerals will become
more available, but some high-cost offshore oil and
gas projects could become unprofitable if the
energy transition speeds up.
• Warming ocean temperatures probably will push
Bering Sea fish stocks northward into the Arctic
Ocean, according to a NOAA study, which could
increase commercial and illegal fishing activity in
the region and exacerbate regional disputes between
Arctic and non-Arctic states over fishing rights.
• Coastal erosion and thawing permafrost will
damage critical infrastructure. Massive investment
in infrastructure would be needed to maximize the
economic potential of the region, ranging from new
ports to mining, offering foreign powers an
opportunity to gain a foothold by investing in new
infrastructure and rebuilding and hardening
existing infrastructure.
Military activity is likely to increase as Arctic and non-
Arctic states seek to protect their investments, exploit
new maritime routes, and gain strategic advantages
over rivals.
The increased presence of China and other non-Arctic
states very likely will amplify concerns among Arctic
states as they perceive a challenge to their respective
security and economic interests. China, France, India,
Japan, South Korea, and the United Kingdom have
released Arctic strategies mostly focused on economic
opportunities, but some address security issues, which
has prompted Russian policymakers to repeatedly state
since 2018 that non-Arctic countries do not have a
military role in the region.
Contested economic and military activities will increase
the risk of miscalculation, and deescalating tensions is
likely to require the adaptation of existing or creation of
new forums to address bilateral or multilateral security
concerns among Arctic states. Although the scope of the
Arctic Council—the leading intergovernmental forum
promoting cooperation among Arctic states—specifically
excludes military security, Russia intends to broach
security concerns with the other Arctic states while
chairing the council from 2021 to 2023, according to
Russian officials’ public statements, and may propose
alternate forums to discuss those issues.

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Increased Strains Over Water and Migration
Outside the Arctic, we judge that transboundary
tensions probably will increase over shared surface and
groundwater basins as increased weather variability
exacerbates preexisting or triggers new water
insecurity in many parts of the world. Forecasted
climate change effects on local and regional weather—
including loss of glaciers and more frequent and extreme
droughts and floods—will make water management,
resource allocation, and service provision more complex
and difficult, and probably more contentious. Although
scientific forecasts are not precise enough to pinpoint likely
flashpoints, we assess that several areas are at high risk.
• Pakistan relies on downstream surface water from
heavily glacier-fed rivers originating in India for
much of its irrigation, and requires frequent data
from India on river discharges in order to provide
advanced warning to evacuate villages and prepare
for flooding.
• The Mekong River basin already is an area of
growing dispute over dam building, largely by
China, that threatens the smooth flow of water for
agriculture and fishing on which other countries rely
heavily, particularly Cambodia and Vietnam.
• In the Middle East and North Africa, about
60 percent of surface water resources are
transboundary and all countries share at least one
aquifer, according to the World Bank. Several
aquifers are also vulnerable to salt water intrusion,
even from minor rises in sea levels, increasing the
potential for conflict.
• Some key bodies for resource management, such as
the Nile Basin Initiative, will increasingly become
sidelined unless they develop enforcement
mechanisms to cajole cooperative behavior among
states. Nearly half the world’s 263 international
river basins—encompassing about half the global
population—lack cooperative management
agreements to help defuse tensions in shared
basins, according to the UN, and most existing
agreements are not flexible enough to address
disruptions in weather patterns and reduced water
flow caused by climate change.
We judge that cross-border migration probably will
increase as climate effects put added stress on
internally displaced populations already struggling
under poor governance, violent conflict, and
environmental degradation. Triggers for increased
migration are likely to include droughts, more intense
cyclones—with accompanying storm surges—and
floods. Given the multiple factors that drive migration
and the uncertainties in regional climate models, we are
unable to project total numbers of climate migrants.
However, countries and displaced people will
increasingly see climate change as a driver, and it will
contribute to instability when it upsets socioeconomic,
political, and demographic dynamics, and strains ties
between originating and receiving countries.
• Around 10 percent of the population of Bangladesh
lives along exposed coastal areas vulnerable to sea
level rise and saltwater intrusion, and the country is
projected to add more than 20 million people by
2040. Since 1993, India has been erecting a fence
along its 4,000-kilometer border with Bangladesh.
• Displaced populations—especially from small
island nations—will increasingly demand changes
to international refugee law to consider their claims
and provide protection as climate migrants or
refugees, and affected populations will fight for
legal payouts for loss and damages resulting from
climate effects.
• The need for investments in adaptation technologies
to manage water stress and reduce a potential driver
of migration could create expanded markets for
advanced technologies, such as water storage and
reuse systems. The UN’s Global Commission on
Adaptation calculates that a $1.8 trillion investment
by 2030 in early warning systems, resilient
infrastructure, dryland agricultural crop production,
mangroves, and water resource management would
yield more than $7 trillion of benefits in avoided
costs from climate change effects.

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Risk of Unilateral Geoengineering Increasing
We assess there is a growing risk that a country would
unilaterally test and possibly deploy large-scale solar
geoengineering technologies as a way to counter
intensifying climate effects if it perceived other efforts
to limit warming to 1.5˚C had failed. Without an
international agreement on these technologies, we
assess that such a unilateral effort probably would
cause blowback. Geoengineering intentionally cools the
planet by reflecting a fraction of solar radiation back to
space or allowing thermal radiation to escape, but it does
not address other climate effects such as ocean
acidification. A large-scale deployment of stratospheric
aerosol injection (SAI)—which mimics the natural
cooling effect of a volcanic eruption by adding small
reflective particles to the upper stratosphere—could have
a global impact. Another technology—marine cloud
brightening—uses aerosols to increase cloud reflectivity
to cool ocean temperatures on a more localized scale.
• Large-scale geoengineering could be internationally
disruptive because of its potential to substantially
affect the Earth’s biosphere, which would change
global weather patterns and provide climate
benefits to some regions at the expense of others.
Depending on the scale and location of deployment,
it could change weather systems in the United States.
• Researchers in several countries, including
Australia, China, India, Russia, the United
Kingdom and the United States, as well as several
EU members, are exploring geoengineering
techniques. We assess that the lack of any country-
level dialogue or governance body to set regulations
and enforce transparency over research increases the
possibility that state or nonstate actors will
independently develop or deploy the technology—
possibly covertly—in a manner that risks conflict if
other nations blame them for a weather disaster they
believe was caused by geoengineering.
Highly Vulnerable Countries of Concern
Key Judgment 3: Scientific forecasts indicate that
intensifying physical effects of climate change out to 2040
and beyond will be most acutely felt in developing
countries, which we assess are also the least able to adapt
to such changes. These physical effects will increase the
potential for instability and possibly internal conflict in
these countries, in some cases creating additional
demands on US diplomatic, economic, humanitarian,
and military resources. Despite geographic and financial
resource advantages, the United States and partners face
hard and costly challenges that will become more difficult
to manage without concerted efforts to reduce emissions
and cap warming.
• The IC identified 11 countries and two regions of
great concern from the threat of climate change.
These countries of concern are highly vulnerable to
the physical effects and lack the capacity to adapt,
suggesting that building resilience to climate change
in these countries would be especially helpful in
mitigating future risks to US interests.
• Five of the 11 countries are in South and East Asia—
Afghanistan, Burma, India, Pakistan, and North
Korea; four countries are in Central America and the
Caribbean—Guatemala, Haiti, Honduras, and
Nicaragua; Colombia and Iraq round out the list.
• Climate change is also likely to increase the risk of
instability in countries in Central Africa and small
island states in the Pacific, which clustered together
form two of the most vulnerable areas in the world.

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• More broadly, developing countries are likely to
need to adapt to a mix of challenges that climate
change will exacerbate. Ineffective water
governance in developing countries will increase
their vulnerability to climate effects, undermining
livelihoods and health. Some will face new or more
intense diseases and lower yields from existing
staples of their agriculture. In addition, insurgents
and terrorists may benefit—we assess that most of
the countries where al-Qa‘ida or ISIS have a
presence are highly vulnerable to climate change.
Select Countries of Concern
We assess that the 11 countries especially are likely to
face warming temperatures, more extreme weather,
and disruption to ocean patterns that will threaten
their energy, food, water, and health security.
Intensifying and more frequent heat waves and droughts
will create water supply volatility and probably strain
their electric utility operations, while growing economies
and populations will increase electricity demands to
handle rising temperatures.
• Warm countries that rely on thermoelectric
power plants for electricity generation are
particularly vulnerable because more frequent
and intense droughts and higher evaporation
rates from rising temperatures are likely to
interrupt their access to water to cool power
plants. Rising temperatures also make the plants
less efficient and more costly to operate.
• For the fifth consecutive year, prolonged dry spells
and excessive rains have devastated maize and bean
crops in Central America’s dry corridor. Yields for
these and other crops in Guatemala, Honduras, and
Nicaragua are projected to decline significantly
because of climate change, according to a UN study,
raising the prospect of food insecurity and a drop in
crucial export commodities.
• More frequent and intense cyclones are likely to
contaminate water sources and increase vector
populations and the diseases they transmit in
several of the 11 countries. Models suggest dengue
incidence probably will increase in Afghanistan,
Guatemala, Haiti, Honduras, India, Iraq, and
Pakistan, according to scientific studies.
• Rising temperatures and increased precipitation
probably will amplify mosquito and diarrheal
disease outbreaks in South Asian and Central
American countries, worsening health outcomes
and causing additional loss of life, according to
scientific studies and the WHO.
• Climate change probably will accelerate the loss
of biodiversity—the variability among all living
organisms—faster than at any point in human
history, leading to more extinctions of plants and
animals that can no longer survive in their
traditional habitats and risking ecosystems that
global populations rely on for food and
medicinal production.
We judge that the 11 countries especially will lack the
financial resources or governance capacity to adapt to
climate change effects, heightening the risk of
instability-induced migration and displacement
flows—including to the US southern border—and
increasing their already substantial needs for foreign
aid and humanitarian assistance. Foreign
governments, international institutions, and private
investment can offer financial aid, technical expertise,
and climate adaptation technologies to alleviate some of
these difficulties—such as food and water insecurity and
urban poverty—but in the 11 countries, these efforts are
likely to be hindered by poor governance, weak
infrastructure, endemic corruption, and a lack of
physical access.
• Several factors have made an outsized contribution
to countries’ declining adaptive capacity, including
being heavily dependent on imported energy and
external resources for health services, and having
low electricity access.
• Climate change is likely to contribute to economic
and social stress and become an increasing
migration push factor, especially for poor farmers
in Central America, who make up 30 percent of the

[ 14 ]
working population. Climate-induced population
movements into cities are likely to compound
factors of social or political instability, such as
uncontrolled urbanization, high rates of
unemployment, and growing slums.
• Diminished energy, food, and water security in the
11 countries probably will exacerbate poverty,
tribal or ethnic intercommunal tensions, and
dissatisfaction with governments, increasing the
risk of social, economic, and political instability.
Regional Arcs of Vulnerability
Climate change is likely to increase the risk of
instability in countries in Central Africa and small
island states in the Pacific. These countries are all
highly exposed to climate change and have little
adaptive capacity. In addition, they are clustered
together to create regions in which the United States or
its allies may be called upon to provide humanitarian
aid, settle disputes, or accept migrants.
Climate change most likely will slow economic and
human development in Central Africa, a region that
already is conflict-prone and heavily reliant on
humanitarian assistance. Countries in the region are
highly exposed to increased droughts, flash flooding, and
related environmentally driven diseases, and also rank
among the lowest in the world in access to education,
electricity, health, and sanitation.
• Under-resourced and ill-equipped militaries will
face severe strains when they are called upon to
respond to more natural disasters in their own and
neighboring countries.
Low-lying Pacific Islands are highly vulnerable to
climate change because of their minimal adaptive
capacity and high exposure to tropical storms and rising
sea levels. Although no island nation is forecast to
disappear by 2040, about 20 percent of their landmass is
projected to face annual wave flooding from higher seas
that will damage infrastructure and threaten food and
water security because of saltwater intrusion of
groundwater resources, according to a 2018 study by
NOAA and USGS.
• Climate change also may hasten the collapse of
commercial fisheries that already are under severe
strain from overfishing, according to the Pacific
Community, which will harm local diets and
economies. Regional fish consumption is three-to-
five times the global average, foreign fishing
licenses make up a large share of government
revenue, and onshore processing provides jobs,
according to a UN study.
Finally, we assess that many other countries are
comparatively more exposed and have fewer resources
to adapt to climate change effects, although some
probably will experience opportunities that mitigate
their challenges.1
The following are illustrative
examples:
• More variable precipitation is likely to widen
China’s south–north water disparity, challenging its
ability to irrigate agricultural areas in its water-
deficient northeast and further drive its dam
construction on rivers upstream from neighboring
countries. However, it is likely to have the
financial and technological resources to compete
successfully in markets for solar and other clean
energies and limit the damage from climate
impacts, such as more intense cyclones and river
flooding.
• North Korea’s poor infrastructure and resource
management probably will weaken its ability to
cope with increased flooding and droughts,
exacerbating the country’s chronic food shortages.
Increasing extremes in seasonal weather variations
may reduce reservoir water stores during droughts
while damaging infrastructure during the rainy
monsoon season.
• Saudi Arabia will face moderate exposure and has
some ability to adapt, while Iran probably will face
more frequent droughts, intense heat waves, and
expanding desertification that, combined with poor
water management, will lower food production and

[ 15 ]
increase import costs during the coming decades,
increasing the risk of instability, localized conflict,
and displacement.
• Egypt is less exposed to climate change effects than
many countries, and Brazil and Mexico have
greater capacity to adapt to such changes.
• Russia is likely to experience infrastructure damage
from permafrost thaw, more frequent and intense
wildfires, and increased erosion. Moreover,
existing agricultural regions probably will
experience longer and more frequent droughts.
Russia, however, will benefit from the opening of
Arctic trade routes and may benefit from longer
growing seasons to increase crop production in
other regions.
The United States and others, however, are in a
relatively better position than other countries to deal
with the major costs and dislocation of forecasted
change, in part because they have greater resources to
adapt, but will nonetheless require difficult
adjustments. Climate impacts such as excessive heat,
flooding, and extreme storms will prove increasingly
costly, require some military shifts, and increase
demands for humanitarian assistance and disaster
relief operations. Adjusting to such changes will often
be wrenching, and populations will feel negative effects
in their daily lives that will become more difficult to
reverse without successful efforts to reduce net emissions
and cap warming temperatures. The impacts will be
massive even if the worst human costs can be avoided.
The energy transition is already rapidly shifting
investment, creating new industries while devastating
others.
• The United States and key states in the developed
world have greater technological capability and
financial resources to adapt to climate change, and
are likely to realize some benefits in terms of
technological competitiveness and agriculture.
Should warmer temperatures and longer growing
seasons yield lower heating costs and increased
agricultural production, most of the beneficiaries
outside Russia are likely to be in the high latitudes,
such as Canada and Scandinavian countries.
• Climate effects are likely to compel militaries in
areas prone to coastal flooding and saltwater
inundation to alter operations, and changes to
ocean temperature and chemistry probably will
require changes to maritime requirements and
sensors, according to a National Defense
University report.2
• Affected militaries also probably will have to adapt
acquisition requirements and expend resources to
harden or rebuild critical infrastructure. The
United Kingdom is expecting increased calls to
respond to humanitarian disasters and is preparing
equipment and designing its forces for a world that
is 2-4˚C warmer than it was in the late 19th
century, according to a UK Ministry of Defense
study released in March.3
Although militaries will
absorb these expenses in normal recapitalization
programs spread over decades, the costs to adapt
will force tradeoffs with other modernization
priorities.
.

[ 16 ]
This NIE’s key judgments are based on assessments regarding the speed of the energy transition away from fossil fuels
and deployment of CDR technologies, the trajectory of intensifying physical effects from climate change, and
countries’ responses to these effects in ways that increase tension and affect US national security. The following four
scenarios highlight some of the developments that could alter our main judgments and their underlying assumptions.
A major breakthrough in and large-scale deployment of zero-carbon energy or CDR technologies would alter our assessment
that the global energy transition is not on pace to meet the Paris Agreement goal of limiting warming to 1.5˚C. Multiple
venture-backed startup companies could utilize their capital—combined with improved computational and materials
science—to develop a breakthrough in nuclear fusion, a near endless source of energy that governments have been
researching since the 1950s without success. In addition, the discovery of a cheap CDR technique or a new and
highly profitable use for CO2 could create a market incentive for companies and countries to remove CO2 from the
atmosphere on a large enough scale to spur a deep decarbonization pathway that results in the globe reaching net
zero emissions well before 2050.
A global climate disaster that mobilizes massive collective action from all countries and populations—such as clear evidence
that we are nearing a tipping point in the Earth’s system faster than expected—would alter our assessment that countries are
going to argue about who bears more responsibility to act. New observations could indicate the irreversible and significantly
faster than expected melting of Greenland and the West and East Antarctic glaciers—which currently are modeled to
raise sea levels by upwards of a quarter meter by 2040, and more than one meter by 2100 under a high emissions
scenario—could threaten hundreds of millions of people living in coastal communities. Alternatively, new evidence
could emerge indicating the near term collapse of the Atlantic Meridional Overturning Circulation (AMOC) that risks
altering North Atlantic air temperatures in excess of 7˚C; current observations give scientists high confidence that
climate change is weakening the AMOC, a critical part of Earth’s climate system that transfers warm water northward
and cold water southward.
Overt military action, especially by a non-Arctic state, that significantly escalates tension in the region and results in a
sidelining of Arctic diplomacy would challenge our judgment that increased activity in the Arctic, while raising the possibility of
miscalculation, is unlikely to result in outright conflict because of the harsh operating environment and existing mechanisms for
cooperation. Persistent challenges to Russia’s supremacy of the Northern Sea Route by a non-Arctic state’s military
could result in armed conflict with Russia if diplomatic negotiations had stalled and foreign militaries continued to
operate in what Moscow views as its territorial waters. Alternatively, if a non-Arctic state, especially China, were to
begin regular, large-scale military operations in the area to protect an economic foothold in the region, the risk of
conflict with Arctic states could increase and contribute to a buildup of forces.
A successful geoengineering deployment at scale that results in global cooling without negatively disrupting weather patterns
would challenge our judgment that unilateral deployment without global consensus would raise international tensions and risk
blowback. A country fearing the existential threat from sea level rise could initiate a geoengineering program that begins
to dim the planet and artificially reduces global temperatures. After witnessing the successful demonstration, other
states might support increased geoengineering, both to avert the worst aspects of climate impacts and to avoid having
to transition away from fossil fuels. Given the lingering environmental impact of emissions and the risk of a massive
climate shock from accumulated emissions if the geoengineering program suddenly ceased, countries probably would
continue to gradually decarbonize energy production and pursue CDR so they could wean off geoengineering.
Annex A: Events That Would Change Our Assessment

[ 17 ]
Scope Note: DOE’s Director of Earth and Environmental Sciences Division authored this annex because he is a member of the
Climate Security Advisory Council (CSAC) and chairs the Interagency Group on Integrative Modeling, which coordinates US
Government modeling efforts in support of the US Global Change Research Program.
Today’s computer climate models trace their origins to the 1950s and the development of prototype atmospheric
circulation models to estimate the distribution of nuclear fallout after an explosion. In 1967, NOAA established a
climate group that produced the first model-based simulations showing that a doubling of CO2 could lead to significant
warming of the Earth’s climate. Ultimately, projections from these and other early modeling capabilities led to the
formation of the Intergovernmental Panel on Climate Change (IPCC).
As of this year, more than 30 major climate-modeling centers worldwide make multi-decadal projections, each with
access to a supercomputer of at least 10-petaflop capacity. The United States and Europe have the most advanced
models, the most notable being NSF’s National Center for Atmospheric Research, NOAA’s Geophysical Fluid
Dynamics Laboratory, NASA’s Goddard Institute for Space Studies, DOE’s national laboratory–led modeling efforts,
Germany’s Max Planck Institute for Meteorology, and the UK Met Office’s Hadley Center. Australia, Canada, China,
Japan, and Switzerland also have modeling centers.
Climate modeling is coordinated worldwide by the World Climate Research Programme (WCRP), which is sponsored
by the UN World Meteorological Organization, International Council for Science, and UNESCO. WCRP helps
scientists exchange information on various model capabilities and strategies. The IPCC produces a climate assessment
every seven years using the ‘all inclusive’ approach by combining predictions from all modeling centers worldwide.
The US Global Change Research Program (USGCRP), on the other hand, produces the National Climate Assessment
every four years using only US models. The USGCRP coordinates efforts across the US climate modeling community
to learn from each other and avoid unnecessary duplication.
Increasing Complexity and Fidelity
The evolution of climate models has been one of increasing complexity run on faster and larger computers. The first
climate models examined how the Earth’s energy balance and atmosphere might vary over time, and only considered
atmospheric physics and rudimentary representations of the oceans and land. In time, scientists added more detail,
such as ocean and land chemistry and biology.
By 1990, better computers meant models could run at 400-kilometer (km) spatial resolutions and make generalized
projections showing that rising levels of atmospheric CO2 increased regional and global temperatures. However, these
models could not display extreme weather events—such as hurricane impacts on cities—because of coarse resolutions,
and they did not include other complicated feedbacks caused by other greenhouse gases or changes in the biosphere,
such as permafrost thaw, ice sheet melt, or deforestation.
Climate models have advanced remarkably in the past 15 years. By 2005, faster computers allowed climate models to run
at 150-km resolution, enabling the representation of some details of human activities such as large-scale energy
infrastructure and agriculture impacts. By 2010, the first petaflop-scale supercomputers and new scientific findings from
field experiments allowed the inclusion of biogeochemical and hydrological processes. By 2015, melting of glaciers and
shelving were included, allowing for better sea level rise predictions, along with greater detail on marine fisheries.
Annex B: The Progress of Climate Modeling—View From the Chair of
the US Interagency Group on Integrative Modeling

[ 18 ]
In 2018, climate models began to include the role of humans and human systems—a major step forward in assessing
climate effects on human security—allowing them to examine the connections between climate, socioeconomics,
global agriculture, infrastructure, and trade on targeted resolutions of 50 km or less. By 2020, US researchers were
testing various methodologies to evaluate the risks and benefits of climate interventions, such as geoengineering.
Evaluating for Accuracy
Scientists are continually testing models for their accuracy in predictions. Climate models operate by solving a very
large set of sophisticated equations for three-dimensional grids in the atmosphere and oceans. The land surface is
more difficult because of the incredible variety of watersheds, ecosystems and glaciers, but modeling centers with the
world’s fastest computers are incorporating variable grid sizes for land features, like glaciers, to obtain more accurate
sea level rise projections.
Scientists use a ‘hindcasting’ technique to test and evaluate the accuracy of models. They run the model from several
decades in the past and compare its projections to real world and long-term observable data from NASA’s remote
sensing satellites, NOAA’s ground-based monitors, and many other US and international agencies. Hindcasting has
shown that models are robust in describing climate warming on continental scales, but not as accurate in projecting
regional phenomena, such as the details of Arctic sea ice retreat, evolving coastal precipitation patterns, and impacts of
storms on human systems. In general, there is reduced accuracy when models project more localized.
Reducing Uncertainty
Current research on reducing uncertainty out to 2050 focuses on two key areas, those caused by overly simplistic or
missing representation of processes and interrelationships, and spatial grids that are not yet small enough to address
key questions. The first set of uncertainties includes: (a) cloud–aerosol interactions; (b) medium-term modes of
variability such as El Niño/La Niña that influence global precipitation patterns and severe droughts; (c) cryosphere
changes such as permafrost thaw, sea ice coverage, and land ice melt that influence methane release and sea-level rise;
and (d) extreme events that impact built infrastructures and populations. Longer-term projections are also sensitive to
scenarios of future policies to reduce greenhouse gas emissions.
Scientists target the second source of uncertainty about spatial resolution by adding details to heterogeneous systems
within smaller grids and porting the models to increasingly powerful computers. In general, the more powerful the
computer, the higher the possible resolution. Most modeling centers are currently operating with 25-km resolution,
with the exception of a DOE model that will operate at 3-km resolution by the end of this year. With the
understanding of key questions from policymakers, warfighters, and the IC, science agencies steer their investments to
tackle and reduce one or more of these uncertainties.
Climate scientists perform tens to hundreds of ensemble runs for each climate simulation, where each run has slight
perturbations on the same initializing data or small changes in parameterizations, in order to reduce the uncertainty
that comes with incorporating larger numbers of complicated and uncertain equations. A modeling center will then
produce an average of all the ensemble runs and compile a best estimate of the future climate. Each modeling center
has a slightly different approach in how they construct their model—such as parameterizations, grid size, and number
of ensemble runs—which means the climate projections from one modeling center may differ from another center.

[ 19 ]
Future Work on Attribution and Tipping Points
Since climate change is increasing extreme weather event trends, a growing field is trying to answer the question of
what fraction of an individual event can be attributed to climate change. Improvements in big data collection and
processing, along with more advanced computers, most likely will advance our knowledge of attribution. In addition,
scientists are working to improve models to better answer the question of when a given component of either the
regional or global climate system will approach or pass a tipping point, an area of high importance given the risks
associated with it—the state of science currently is still unable to adequately answer this question.

[ 20 ]
The macroeconomic impacts of climate change out to 2040 are highly uncertain because of the divergent estimates
and methodological approaches employed in a wide range of economic models, including different assumptions,
baselines, time horizons, and variables. The future economic impacts of climate change will also depend in large
part on the extent to which policies and actions mitigate these potential impacts, further complicating longer-term
estimates of costs and benefits.
A key variable is the potential for technological breakthroughs that substantially favor varying mixes of energy
production and distribution and of carbon removal and storage. In recent years, a growing number of studies have
argued that pursuing mitigation and adaptation measures can also provide opportunities to spur economic growth,
potentially by more than the dislocations and disruptions projected for some economic sectors, such as oil and gas.
• Other economic and many climate experts argue that existing assessments of the potential future economic risks
of climate change underestimate many of these risks, possibly greatly. In particular, they argue that widely used
models omit many factors that are difficult to quantify, discount future costs and benefits, and fail to consider
climate thresholds, tipping points, or the dynamic impact of numerous shocks.
• Some researchers argue that the physical impacts of climate change, including the destruction of infrastructure
and physical capital, disruptions in global supply chains, and more unpredictable food commodity supply
cycles, could lead to more output and price variability and pose significant additional challenges in forecasting
macroeconomic impacts.
As a result, we judge that state and nonstate actors will increasingly push for regulations mandating climate change–
related risk disclosure in the financial system to protect against these macroeconomic impacts. The United States will
have opportunities to influence regulatory frameworks and reporting standards.
Annex C: Challenges of Projecting the Macroeconomic Impacts of Climate Change

[ 21 ]
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1
Report, Think tank; Atlantic Council; 10 FEB 2020; A New Security Challenge: The geopolitical implications of
climate change; www. Atalnticcouncil.org/blogs/energysource/a-new-security-challenge-the-geopoliotical-
implications-of-climate-change/.com, Accessed 6 April 2021.
2
Academic report, National Defense University; Richard Pittenger and Robert Gagoisan; OCT 2003; Global Warming
Could Have a Chilling Effect on the Military.
3
UK Ministry of Defence, “Ministry of Defence: Climate Change and Sustainability Strategic Approach,” March
2021.

US National INtelligence Estimate: Climate change and international response

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US National INtelligence Estimate: Climate change and international response