The Caspian Sea, the world’s largest lake, accounting for about one-third of the Earth’s surface water. That lake is rapidly changing. According to research published in the journal Nature in April 2025, the Caspian’s level could drop by up to 21 meters by 2100, using the 1990 Caspian elevation of -27.5 meters as a baseline. It is further noted that a drop of just 5 meters would eliminate 20% of the Caspian’s current surface area. Moreover, even a water-level decline of only 5 to 10 meters could reduce existing marine protected areas by as much as 94%.

As with the Aral Sea, once the world’s fourth-largest lake, which has shrunk to less than one-tenth of its original area and is undergoing desertification due to large-scale irrigation projects since the 1960s, will the Caspian Sea also disappear? Let’s examine the Caspian’s current situation and its effects.

The Caspian Sea photographed from the International Space Station (Photo: Alexander Gerst / Flickr [CC BY-NC-SA 2.0])

Basic facts about the Caspian Sea

First, let’s understand some basic facts about the Caspian Sea. The Caspian lies east of the Caucasus Mountains and borders five countries: Kazakhstan, Turkmenistan, Iran, Azerbaijan, and Russia. The main rivers feeding the Caspian are to the north—the Volga, Ural, and Terek—and inflows from these rivers account for 88% of the total. On the other hand, there are no permanent rivers along the Caspian’s eastern shore except for the Atrek River in southern Turkmenistan. Although the water flowing into the Caspian from rivers is fresh, salts and minerals from the soil dissolve into the sea, making it unsuitable for use as freshwater.

Backed by these abundant water resources, many peoples, including the Caspians from whom the sea gets its name, have made the Caspian and its surroundings their base. It was part of the Silk Road and has long served as an important hub of trade, culture, and diplomacy up to the present day. Today, as a route enabling trade from Asia to Europe without passing through Russia, it has gained attention under the name “Trans‑Caspian International Transport Route.”

The most important resources obtained from the Caspian are natural gas and oil. In 2022, offshore natural gas production in the Caspian accounted for about 3% of the world’s natural gas supply, while oil production accounted for 1% of the global oil supply. It is also very famous for fisheries; in particular, caviar from sturgeon caught in the Caspian boasts the world’s largest production.

Babolzar Beach on Iran’s Caspian coast (Photo: daniyal62 / Flickr [CC BY-NC 2.0])

Who owns the Caspian Sea?

Being rich in natural gas and oil, the Caspian Sea has long been a stage for international maneuvering over “who owns it.” Prior to the collapse of the Soviet Union in 1991, the Caspian was controlled solely by Iran and the USSR. However, after the Soviet collapse, three newly independent states—Azerbaijan, Kazakhstan, and Turkmenistan—joined Iran and Russia in asserting claims to the Caspian, and the dispute gradually intensified. For many years, even the basic definition of whether the Caspian was a sea or a lake had not been decided. If the Caspian were defined as a “sea” and international maritime law applied, non-littoral countries might gain access rights to the Caspian, providing a legal basis for foreign warships to sail it—prompting opposition from some states concerned about this. Conversely, if the Caspian were treated as a “lake,” an equal division agreement among the five coastal states would apply, requiring an equal distribution of seabed resources regardless of coastline length—something other states opposed.

While the boundary dispute remained unresolved, various incidents occurred among the littoral states. In 2001, tensions between Iran and Azerbaijan over development of a hydrocarbon field in the Caspian nearly escalated into armed conflict. After years of confrontation, in 2018 the five coastal states finally concluded a convention on the legal status of the Caspian Sea. This granted the waterbody a “special legal status” distinct from a sea or a lake, and the surface waters of the Caspian were to be used jointly by the coastal states. However, specific issues such as distribution of seabed resources remain left to separate negotiations, leaving many issues unresolved.

Water-level fluctuations and pollution

In this Caspian Sea where the interests of five countries swirl, the gradual fluctuation of water levels is having serious effects on the region. Many studies have examined Caspian water-level changes, but as noted at the outset, a drop of up to 21 meters by 2100 has been suggested. There is also a projection that a 5‑meter drop alone would shrink the Caspian’s area by 20%, exposing 77,000 square kilometers of land.

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This chart shows changes in Caspian water levels in Baku, the capital of Azerbaijan, from 1990 to 2024. Until 1978, the Caspian’s level exhibited year-to-year fluctuation within a longer-term declining trend, mainly due to reduced inflows caused by human activities such as irrigation and dam development. However, from around 1978 to 1995, levels rose sharply. This increase is thought to have been driven by reduced evaporation associated with a temporary cooling in the Volga River basin and a scaling back of irrigation projects.

After 1996, levels began falling again, with a particularly rapid decrease in recent years. Behind this are reduced precipitation and increased evaporation due to global warming, and changes in industrial structures after the Soviet collapse are also thought to have played a role. This chart illustrates how climate change and shifts in human industrial activity strongly influence water-level fluctuations.

The Caspian coastline has advanced and retreated repeatedly, but especially in the 20th century, changes in inflows and precipitation and increased evaporation are considered the causes of water-level variability. The Volga River in Russia, which supplies about 80% of inflows to the Caspian, is a key factor. Russia had 11 dams along the Volga as of 2021, reducing the water entering the Caspian. It has also been suggested that around the time Russia invaded Ukraine in 2022, it may have deliberately reduced inflows to the Caspian. Facing shortages of imported agricultural products due to Western economic sanctions, Russia is believed to have diverted more Volga water for agriculture as irrigation to boost domestic production.

Even more affected by rising temperatures is evaporation. One study finds that increased evaporation contributes more to changes in the Caspian than river inflows or precipitation do. There is a projection that the average temperature over the Caspian could rise by about 3.64 degrees by 2100, suggesting evaporation will continue to increase.

Falling water levels have especially large impacts on shallow areas. According to the World Database on Protected Areas (WDPA), protected areas designated by Kazakhstan in the Caspian account for 16.8% of the entire sea. However, because most of these are situated along the coast, a 5‑meter drop is expected to reduce protected areas to 7% of their current size, and a 10‑meter drop to just 1%. At this rate, it is highly likely that today’s protected areas will vanish by 2100.

Another major issue the Caspian faces is water pollution. Large-scale oil and gas extraction has led to contamination by toxic heavy metals such as mercury and cadmium. It has also been suggested that toxic substances in the fuel of missiles Russia has launched from the Caspian during its invasion of Ukraine may be raining back down into the sea, worsening pollution. Because the Caspian is a closed basin, pollutants discharged into it do not flow out elsewhere, leading to accumulation within the sea.

Impacts of Caspian changes on the environment and people

These environmental changes and pollution raise major concerns for biodiversity. The Caspian hosts more than 222 endemic invertebrate species (excluding protozoa and parasites) and 31 endemic fish species, as well as valuable ecosystems such as the Caspian seal. However, unplanned human activities have degraded these ecosystems.

The Caspian seal population has declined by 90% over the past century, from 1.2 million in the early 20th century to an estimated 75,000 to 270,000 today, and future water-level changes could drive further declines. Historically, for most of the 20th century, seal hunts were carried out under state direction for fur and oil derived from Caspian seals. Today, with the species listed as Endangered by the International Union for Conservation of Nature (IUCN), hunting is banned in all five littoral states, yet the decline continues.

In recent years, there have been repeated observations of mass die-offs of Caspian seals. While various causes have been proposed, water pollution and reductions in sea-ice extent are considered primary factors. As noted above, pollution in the Caspian is severe. It is suspected that this pollution has affected seals’ immune systems, facilitating the spread of infectious diseases. Indeed, in October 2024, along the coast of Russia’s Republic of Dagestan, which has been discharging inadequately treated wastewater into the Caspian, only one seal was recorded. Experts warn that fish and other seal prey may also be contaminated with toxins. Moreover, the reduction of winter sea ice is shrinking seal habitat; specifically, a 5‑meter drop in water level could reduce habitat by up to 81%. Typically, Caspian seals move north in winter and breed on the ice in the northern part of the sea, but they may lose their breeding grounds.

A Caspian seal in the Caspian Sea (Photo: Aboutaleb Nadri / Wikimedia Commons [CC BY 4.0])

Sturgeon, famous for producing caviar, are likewise affected in their habitats and spawning grounds. As shallow areas shrink with water-level changes, sturgeon movement is hindered, and they may be unable to reach rivers where they spawn. Changes in fish populations mean smaller fisheries on the Caspian. Although sturgeon capture is currently banned, many people continue to illegally catch them. Declines in catches of other fish are also a concern. For example, in Kazakhstan, catches of catfish and trout have fallen, prompting temporary fishing bans to protect remaining stocks. If the Caspian continues to shrink, salinity will increase further, making the environment less hospitable for fish and potentially reducing catches.

These conditions are also affecting human societies. As catches have continued to decline in recent years, many fishermen in littoral states can no longer sustain their livelihoods from fishing alone. As the sea shrinks, toxic dust previously deposited on the seabed dries and is carried by the wind, increasing the risk of respiratory illnesses among millions of people. Sandstorms are becoming more frequent, affecting agriculture as well. For these reasons, of the 15 million people currently living around the Caspian, up to 5 million could be forced to relocate by mid-century.

A shrinking Caspian and its geopolitical implications

The Caspian Sea plays a crucial role as a strategic hub for trade and energy transport linking Central Asia, Europe, and China. Before Russia’s 2022 invasion of Ukraine, more than 90% of rail shipments between Europe and China transited Russia. Since sanctions, efforts have focused on expanding routes that bypass Russia. Among them, the Trans‑Caspian International Transport Route has gained importance for the European Union (EU) as a route to trade with China without transiting Russia or Iran, boosting its geopolitical significance. Cargo from China and elsewhere crosses the Caspian from Kazakhstan’s Aktau and Kuryk ports to Baku or Alat in Azerbaijan, and is then transported overland to Europe.

This mode avoids Russia and Iran, which have been subject to Western economic sanctions, strengthening supply chains for the EU and China. Especially since Russia’s invasion of Ukraine, trade via the Trans‑Caspian route has increased, and the World Bank projects that by 2030 traffic will be three times the 2021 level. China and the EU already have high expectations for this corridor, investing in developing the logistics facilities needed for trade and in improving transport networks in Central Asian countries.

Based on data from Middle Corridor.

However, the risk of falling Caspian water levels has begun to cast a shadow over these economic plans. By 2100, key ports may become completely inoperable for trade. In the worst case, Turkmenistan’s Turkmenbashi port and Russia’s Lagan port could end up 16 kilometers and 126 kilometers, respectively, from the shoreline. Beyond ports, infrastructure such as oil refineries and natural gas processing facilities could also end up more than 5 kilometers farther from the coast. The resulting economic losses from water-level changes could exceed tens of billions of U.S. dollars per year.

Meanwhile, another flashpoint is emerging: water scarcity. As GNV previously reported, Central Asia has seen conflicts over dwindling water resources in recent years. In the Caspian region, Kazakhstan, Azerbaijan, and Iran are building or considering desalination plants. Desalinating Caspian water is relatively less costly because it is less saline than typical seawater. These countries plan to use the water for agriculture, domestic needs, and green hydrogen production. On the other hand, there are concerns that desalination could cause environmental pollution and further water-level decline, potentially accelerating future disputes over Central Asia’s water resources. Developments in the Caspian are therefore crucial for regional stability.

COP29 and the Caspian Sea

In light of this situation, the 29th Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCC COP29) held in Baku, Azerbaijan, in 2024 took up the issue of falling Caspian water levels as a key agenda item. However, the discussions did not proceed easily. The host, Azerbaijan, was reluctant to restrict fossil fuels, even calling them a “gift from God.” Yet consumption of such fossil fuels drives climate change and contributes to the Caspian’s decline, exposing a contradiction in Azerbaijan’s position.

A jack-up drilling rig extracting oil in the Caspian Sea (Photo: www.dragonoil.com. / Wikimedia Commons [CC BY-SA 3.0])

Iran, for its part, had done little over the past decade to address climate change, which is accelerating the Caspian’s decline. Expectations therefore grew that Iran’s participation in COP29 might signal changes in its environmental policies. In reality, Iran’s stance remained passive toward environmental protection, and its policy of not joining the Paris Agreement of 2015 was unchanged. COP29 highlighted the difficulty of regional cooperation to protect the Caspian. Countries appear fixated on short-term national interests while neglecting long-term environmental efforts. Geographically enclosed, the Caspian cannot be protected effectively without cooperation among all littoral states.

At the same time, some measures to address these climate-driven problems are emerging. At COP29, Azerbaijan, Kazakhstan, and Uzbekistan signed a “Trilateral Agreement on Strategic Partnership in the Field of Green Energy Development and Transmission.” The three countries plan to lay power cables across the seabed of the Caspian and the Black Sea to supply renewable energy to Europe.

The region holds significant potential for renewable energy production. By leveraging geographic conditions and abundant natural resources, littoral states aim to reconcile climate action with economic development. Kazakhstan in particular has extremely high wind and solar potential and is said to have the potential to exceed the world’s wind power generation on its own. These initiatives are expected not only to break dependence on fossil fuels but also to strengthen energy security. Moreover, building the capacity to import renewable energy would be an important step for the EU toward a decarbonized society. As such regional cooperation progresses, the Caspian could become a central player in international climate action.

For the future of the Caspian Sea

The Caspian’s future will be greatly influenced by the choices of its surrounding countries. Without cooperation and sustainable measures that transcend short-term gains, the contraction of this inland sea could inflict irreparable harm on the region’s ecosystems, environment, and economy. To protect the Caspian Sea—renowned as the world’s largest inland sea—now is the time for genuine cross-border collaboration.

Writer: Ito Risa

Graphics: Ayane Ishida

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