Information about past climates is melting away along with the ice.

Climate scientists gather information about the properties and parameters of the main climate spheres (atmosphere, hydrosphere, biosphere, lithosphere, and cryosphere) and the exchange processes between these spheres through a well-developed observation system. Although the global climate observation system as a whole was established only in the early 1990s, its individual components have been in place for decades. Overall, the era of instrumental climate observations has lasted for more than 170 years and includes various forms of observation. The tools for observation are continually being improved, increasing accuracy and coverage, while increasingly "subtle" phenomena are being studied. For instance, the flows of greenhouse gases from ecosystems, heat accumulation in the ocean, the volume of ice in glaciers, the absorbing properties of aerosols, the location and intensity of lightning strikes, etc.

In the 19th century, the primary observations were instrumental ship observations or measurements at meteorological stations, but now the main flow of information comes from automatic observation tools. These include contact observations, such as automatic weather stations, buoys, gliders, sensors placed on airplanes and drones, and so forth, as well as remote sensing instruments—spectroradiometers, radars, lidars, sodars. These instruments are located both on Earth and in space, on satellites. For example, by measuring anomalies in Earth's gravitational field, scientists studied the reduction of ice volume in the Greenland and Antarctic ice sheets. Changes in incoming solar radiation in narrow spectral channels allow climatologists to record the properties of aerosols, tiny solid and liquid particles suspended in the air, which significantly influence cloud physics, air quality, and the planet's climate. Long-term observation programs for the ocean and atmosphere, such as the PIGAP (Program for Investigating Global Atmospheric Processes), "Cross-sections," and others, have also made significant contributions.

Russian and Soviet scientists have made substantial contributions to the development of climatology. For instance, M. F. Spassky was one of the first to formulate the problem of climate assessment as a physics problem, A. I. Voeykov created one of the first climate atlases in the world and began studying the energy budget of the surface, A. M. Obukhov described the fundamental law of atmospheric turbulence, and M. I. Budyko calculated the Earth's thermal balance and created one of the first semi-empirical climate models, using it to assess the conditions for equilibrium climate (see more in the chapter “We Need to Explain Something”). G. I. Marchuk introduced splitting methods into numerical weather and climate modeling, and S. S. Lappo discovered the presence of global thermohaline circulation in the ocean. This is far from a complete list of discoveries—enumerating and understanding all the achievements of Russian climatology could fill pages. Currently, research in climate and related areas (adaptation, mitigation) is conducted by scientific teams from dozens of organizations within the Russian Academy of Sciences, Rosgidromet, and higher education institutions.

Thanks to observations, we know that in recent decades, the concentration of greenhouse gases in the atmosphere (primarily carbon dioxide, but also methane and nitrous oxide) has been rapidly increasing. Observations of the isotopic composition of CO₂ in the atmosphere have allowed a confident attribution of the cause of this increase to the burning of fossil fuels, which have almost no unstable isotope ¹⁴C. Observations of greenhouse gas flows also support this conclusion. (see more in the chapter “We Need to Explain Something”) The increase in greenhouse gas concentrations, in turn, leads to an intensification of the greenhouse effect: this intensification is well documented by multispectral observations of the longwave radiation coming from the atmosphere. Thanks to the developed network of observations, scientists also see the results of this intensification: warming in the lower layers of the atmosphere and at the surface (for example, 2023 was 1.45 ºC warmer than the second half of the 19th century) and sharp cooling in the upper layers of the atmosphere.

The intensification of the greenhouse effect due to anthropogenic CO₂ flows constantly deviates the planet from radiative equilibrium. Satellite systems detect Earth's energy imbalance: the incoming radiant energy from the Sun amounts to 340 W·m^–2, while the outgoing radiation to space is only 339 W·m^–2. In recent years, advanced observation systems have allowed scientists to close this imbalance and understand where this 1 W·m^–2 "goes": they have established that primarily this difference contributes to ocean warming (about 90%).

Another significant achievement in recent years has been determining all the components of the observed sea-level rise, which has accelerated from 2 mm per year in the 1990s to nearly 5 mm per year today. Scientists have established that the primary contributor to this rise is the melting of glaciers, particularly ice in Greenland.

Melting ice gradually carries away information about past climates, which continues to be of great interest for research. Here, scientists utilize natural "archives" that contain useful signals about past climates: isotopes in tree rings and sediment cores, air composition in bubbles trapped in ice, and so on.

The role of the ocean, including the Arctic, in climate change is actively researched at the P. P. Shirshov Institute of Oceanology, the Arctic and Antarctic Research Institute, and the V. I. Ilyichev Pacific Oceanological Institute. The hydrosphere of land as part of the climate system is studied at the Institute of Water Problems of the Russian Academy of Sciences, the State Hydrological Institute, while issues related to the cryosphere and processes in permafrost are addressed by scientists at the Earth Cryosphere Institute of the Siberian Branch of the Russian Academy of Sciences and the P. I. Melnikov Permafrost Institute of the Siberian Branch of the Russian Academy of Sciences.

Additional examples of observations can be found in the chapter “We Need to Explain Something”.

Modeling and Climate Forecasting

In science, the ability to conduct experiments is crucial for confirming or disproving a hypothesis. Therefore, climatology relies not only on observations and paleoreconstructions. Observational campaigns are organized and conducted to clarify specific mechanisms of the climate system. For instance, as early as the late 19th century, F. Nansen proposed the hypothesis of the existence of transpolar drift in the Arctic and tested it by freezing his ship, Fram, in the ice of the Laptev Sea and freeing it from the ice near Spitsbergen.

But what if a global experiment needs to be conducted? For example, how will temperature respond and how will circulation change if we double the planet's rotation speed, or reduce the amount of energy received from the Sun by 10%? Or if we double the concentration of greenhouse gases in the atmosphere? Understanding the response of atmospheric circulation can be partly aided by hydrodynamic laboratory experiments with rotating systems. But what about global temperature? There isn’t a second planet nearby to conduct a natural experiment on.

The solution lies in building climate models, which are essentially climate twins, and conducting experiments with these models. Such models, evolving from simple conceptual or energy-balance models, have now grown into models of general atmospheric and oceanic circulation, where hydrodynamic equations, radiation transfer, phase transitions of water, etc., are computed using finite difference schemes (see more in the chapter “We Need to Explain Something”). Essentially, modern climate models are weather prediction models with somewhat coarser resolution in the atmosphere (instead of kilometers—tens of kilometers), but with other interactive components (such as vegetation, deep ocean, glaciers, carbon cycle), which are not required for weather forecasting but are vital for climate research.

A large number of experiments are currently being conducted with climate models, including ensemble experiments (where not just one model run is done, but dozens and hundreds of runs), coordinated among scientific groups (models are compared with each other). The role of clouds and aerosols in climate, the role of greenhouse gases, and natural variability are being investigated. In particular, models show that considering only natural factors (such as solar activity variability, orbital parameters, volcanic eruptions) cannot explain current warming, while taking both natural and anthropogenic factors into account allows models to reproduce warming quite reliably. Climate forecasts based on climate models made decades ago have successfully held true: model calculations from the 1970s successfully predicted temperature rise, and later calculations predicted both sea-level rise and even acceleration of that rise. Moreover, forecasts made not only in research institutes but also in large