Is the Caspian Facing the Fate of the Aral Sea?

In less than 20 years, the surface area of the Caspian Sea has shrunk by more than 34,000 square kilometers. For comparison, this is larger than one of Africa's largest lakes — Lake Tanganyika (32,900 km²), or Belgium (32,545 km²), and even more than the territory of 138 other countries around the world. In addition, the water quality in the Caspian has deteriorated — from “clean” to a “moderate level of pollution,” with periodic exceedances of the maximum permissible concentrations of harmful substances. Experts from the Central Asian Climate Fund have prepared a review of the Caspian’s most pressing environmental issues.

Uniquely Caspian

The Caspian Sea is unique as the largest enclosed inland body of water in the world, with no connection to the global ocean. Technically, it is a landlocked lake, though its origin traces back to the ancient Tethys Ocean. The seabed of the Caspian consists of oceanic-type earth crust, which allows it to be classified as a closed inland sea.

The water in the Caspian is brackish, and salinity levels vary throughout the sea — becoming higher in the southern parts.

The Caspian is also among the deepest lakes in the world, along with Lake Baikal and Tanganyika.

The Caspian is home to numerous animal species, including the endemic Caspian seal, and hosts the largest sturgeon spawning grounds on Earth.

Shrinking Waters

As an enclosed basin, the Caspian Sea is subject to significant fluctuations in water level, caused by changes in the water balance — itself influenced by climate change and human activity, especially related to rivers feeding the sea.

Around 130 rivers flow into the Caspian. By the early 1970s, virtually all major rivers in the basin had been regulated. Of the total river inflow, 86.1% comes from the Volga River, 5.1% from the Kura River, 2.9% from the Ural River (which has significantly decreased), 2.4% from the Terek River, and 3.5% from other rivers.

Due to its vast territory and remoteness from the ocean, the climate in the Caspian region is warming significantly faster than the global average, and even faster than the territory of Kazakhstan.

According to Kazhydromet, between 1976 and 2024, the change in the average annual air temperature was +0.19°C per decade globally, +0.36°C per decade in Kazakhstan, and +0.51°C per decade in the Caspian region.

During the period of systematic observation (from 1900 to 2023), the sea level has ranged from minus 25.74 meters BHS (in 1900) to minus 29.01 meters BHS (in 1977).

BHS (Baltic Height System) is a unit of measurement for elevation and depth, referenced from the zero level of the Kronstadt tide gauge.

Throughout the history of Caspian Sea observations, there have been several periods of sea level rise and fall:

- from 1940 to 1977, the sea level dropped at a rate of 4 cm per year (a total drop of 1.2 m);

- from 1978 to 1995, it rose at a rate of 13 cm per year (a total rise of 2.5 m);

- from 1996 to 2023, it fell again at a rate of 8 cm per year (a total drop of 1.83 m).

At present, the decline of the Caspian Sea continues. From 2006 to 2024, it dropped by 2.14 meters. In the first half of 2025, the average sea level was −29.28 meters BHS.

According to the State Oceanographic Institute (Russia), as a result of the sea level decline since 2006, the surface area of the sea has decreased by 34.4 thousand km² — from 392.3 thousand km² to 357.9 thousand km².

Satellite data from NASA for the years 2020–2025 show that the Caspian is shrinking at a rate of about 7 cm per year. This is 20 times faster than the current rise in global ocean levels. If this trend continues, by 2050, the northern part of the sea, where the depth does not exceed 5 meters, may almost completely disappear.

Scientific forecasts vary depending on the climate change scenario. By the year 2100, under the optimistic scenario (a temperature increase of +1.5°C), the sea level could drop by 5–9 meters; under the realistic scenario (+2–3°C), by 10–15 meters. A catastrophic but possible scenario, involving warming of +4°C or more, would result in a drop of 18–21 meters.

If the latter scenario materializes, the surface area of the sea would shrink by 30%, and the volume of water would be reduced by nearly half.

Pollution

Another major issue affecting the Caspian Sea is water pollution caused by active oil extraction.

Monitoring of water quality in the Caspian Sea within Kazakhstan’s territory is conducted at 50 coastal points, 22 of which are located in the Northern Caspian and 28 in the Middle Caspian.

According to Kazhydromet, between 2005 and 2018, the water quality in the Caspian ranged from “clean” to “moderately polluted.”

In the Northern Caspian, exceedances of the maximum permissible concentration (MPC) were recorded between 2007 and 2009 for copper, total iron, and nitrite nitrogen. In 2009, chromium (VI) exceeded MPC by 1.2 times; in 2013, by 1.1 times. Between 2010–2012 and 2014–2018, no exceedances were found.

In the Middle Caspian, exceedances of MPC were observed in certain months during 2006–2008 and 2010–2012, primarily for copper, manganese, zinc, chromium (III) — 1.1 times the MPC in 2011 — and petroleum products. In 2013–2014, levels of petroleum products exceeded the MPC by 1.2–2.3 times. No exceedances were recorded from 2015 to 2018.

Since January 2019, Kazakhstan has adopted a Unified Water Quality Classification System for surface water bodies. This system compares current values with long-term observations and includes six water quality classes — from "best" to "worst." It accounts for the requirements of various types of water use: ecosystem support, fisheries, drinking water, recreation, irrigation, industry, hydropower, and transport.

According to Kazhydromet, in 2019 the water quality in the Caspian Sea was assessed as “above class 5” — meaning it was unsuitable for any type of water use. In recent years, there has been no trend toward worsening pollution.

Extinction

The Caspian Sea began forming 5–7 million years ago, when the ancient Tethys Ocean split into smaller water bodies. As a result of this geological history and its isolation from the global ocean, the Caspian developed a unique ecosystem with endemic species of flora and fauna that now risk extinction.

The population of Caspian seals has declined by 90% over the past 100 years — from around 1.2 million in the early 20th century to fewer than 100,000 today. This species, endemic to the Caspian Sea, is now critically endangered.

Unlike most seals, Caspian seals breed exclusively on ice floes in the northern part of the sea during January and February. Pregnancy in females lasts 11 months, so any disruption to this reproductive cycle immediately affects population numbers.

Studies conducted in 2023–2024 show that the area of winter sea ice in the Caspian has decreased by 40% over the past 20 years. A sea level drop of 5 meters would reduce suitable ice coverage for seal breeding by 81%.

Seals also require “haul-out sites” — areas on land where they gather to rest, molt, and reproduce. As water recedes, traditional haul-out sites become inaccessible, and newly formed shallows and islands often do not meet the seals’ needs.

Water pollution and a shrinking food supply due to overfishing also negatively affect the seal population. Many animals die in fishing nets.

The Caspian Sea is also home to six species of sturgeon: beluga, Russian sturgeon, Persian sturgeon, stellate sturgeon (sevruga), ship sturgeon, and sterlet — all of which are now threatened with extinction. As the sea level drops, river deltas become shallower, preventing fish from reaching their spawning grounds. In addition, feeding areas in the shallows — which are the first to disappear when water levels fall — are vanishing. Poaching continues to inflict serious damage on sturgeon populations.

“The shrinking of the Caspian Sea is a real and urgent problem, caused by a combination of climate change, reduced river inflow, and other factors. The sea level is falling, exposing new land areas, reshaping the shoreline, and bringing serious ecological and economic consequences.

The mission of our foundation is not only to draw the attention of Caspian-bordering countries to this issue but also to engage the global community in finding solutions to prevent a repeat of the Aral Sea tragedy,” said Yerlik Karazhan, Head of the Project Office for Central Asia on Climate Change and Green Energy of the Central Asian Climate Fund.

He added: “A special session on the Caspian Sea crisis will be held at the Regional Environmental Summit in Astana in 2026.”.