"The threat of the Venereal variant rises as anthropogenic warming continues." An interview with Igor Mokhov.

— Igor Ivanovich, I took the time to read your works before the interview and came across the infamous "climatic optimum." I had the impression that this optimum might have been associated with the medieval warm period...

— I was referring to the Holocene optimum.

— …and that it should have already ended by now...

— The Holocene is a stage of the interglacial period, characterized by the highest temperatures at the Earth's surface during what is known as the Holocene optimum — several millennia ago. The Holocene stage has been ongoing for over 11,000 years and, it seemed, should have come to an end with the transition of the Earth into another cooling phase. This is linked to changes in the parameters of the Earth's orbit around the Sun, occurring over periods of about 20, 40, and 100 thousand years, known as Milankovitch cycles — named after the Serbian scientist Milutin Milanković. These changes are associated with the formation of glacial cycles on Earth over the last approximately two million years. Why did such glacial cycles not manifest earlier, despite orbital changes? The fact is that over the last several tens of millions of years, the average surface temperature of the Earth has been declining. This is also linked to greenhouse gases, the main one being water vapor. In the absence of an atmosphere containing water vapor, the surface temperature of our planet would be over 30 ^оC lower. However, the characteristic lifetime of water vapor in the atmosphere is only a few days (its concentration in the atmosphere depends on the temperature regime). In contrast, the lifetime of the greenhouse gas CO₂ in the atmosphere is much longer — on the order of a hundred years. Throughout Earth's history, there have been epochs when CO₂ concentrations were an order of magnitude higher than they are now. With the cooling of the planet over the last tens of millions of years, the role of snow and ice cover has intensified. The albedo of snow and ice is associated with a strong positive feedback that amplifies the impact of changes in the Earth's orbit: the more ice and snow there is during a temperature drop, the more solar radiation is reflected back into space, leading to a further decrease in the planet's temperature. Around 2 million years ago, changes in the parameters of the Earth's orbit began to manifest significantly in the form of glacial cycles. Over the last million years, the cyclical nature associated with the eccentricity of the Earth's orbit around the Sun, with a period of about 100 thousand years, has dominated. By now, the Earth has passed the temperature maximum of the Holocene optimum, and one could expect a continuation of cooling; however, the temperature of our planet is not only not falling but is rapidly rising.

— So, are we currently living in some kind of unclear fluctuation?

— According to modern research findings, the rapid warming we are experiencing now is linked to the intensification of the greenhouse effect due to anthropogenic emissions of greenhouse gases into the atmosphere, primarily CO₂. It is no coincidence that this era has been termed the Anthropocene. There are already model estimates suggesting that depending on the emissions of greenhouse gases, Earth may not enter another glacial period for the next several tens of thousands of years. This depends on how much greenhouse gas will be released into the atmosphere. We conducted numerical calculations using a global Earth system model for the last millennia, including the Holocene optimum, and for hundreds of years into the future under various scenarios of anthropogenic impacts. According to the model results obtained, in recent years, the modern climate has already reached the level of the Holocene optimum or even surpassed it on a regional scale, particularly in the Yamal Peninsula area and adjacent regions, indicating anthropogenic influence on the climate at a geological scale. The formation of known craters in Yamal also suggests that the current warming, with the thawing of permafrost, has reached a level comparable to that of the Holocene optimum. This may lead to the destabilization of shallow methane hydrates and the release of methane into the atmosphere.

— Are they really breaking through?

— This was first noticed in 2014. Later, an analysis of earlier satellite images revealed that such breakthroughs are associated with the formation of round-shaped lakes. There are many such lakes on the Yamal Peninsula and in adjacent regions. After a breakthrough, the permafrost melts rapidly, and lakes form within a year or two.

— But if this process were to occur not fragmentarily, but all at once, it would pose a very serious danger?

— The degradation of methane hydrates due to global warming could be associated with serious climatic issues. As a greenhouse gas, methane is over 20 times more radiatively effective than CO₂ on a per molecule basis. However, there are many uncertainties regarding both their reserves and their stability. According to our model estimates, the climatic effect of potential methane hydrate degradation in the 21st century is relatively weak. This is a potentially very important problem, as permafrost covers almost two-thirds of Russia's territory. We have been studying this issue for a long time. Once, I believe in the early 2000s, I gave a presentation on this topic at a European symposium, and the section chair asked me, “Methane bomb?” I replied, “Potential.”

— Since the ice is melting, it could lead to a methane bomb.

— About a decade and a half ago, we conducted modeling using a proposed simple model that allows for analytical estimates. We assessed at what level of warming the Antarctic ice sheet could begin to melt. Surprisingly, at first, it should actually grow with warming. The increase in atmospheric moisture capacity leads to more precipitation, and at negative temperatures in the Antarctic latitudes, this means snow, which increases snow reserves. However, once a certain critical global temperature is exceeded, the melting of the Antarctic ice sheet begins to dominate. We estimated that the critical increase in global near-surface temperature is 1.6 ^оC. On a global level, even tenths of a degree are significant. According to the conditions of the Paris Agreement on climate change (2015), which Russia also signed, global warming relative to pre-industrial levels must not exceed 2 ^оC, with a preferable limit of 1.5 ^оC. According to our estimates, at one and a half degrees of global warming, the Antarctic ice sheet can still maintain stability, while at a 2 ^оC increase, it should start to melt.

— So we are now approaching a critical threshold?

— The situation is developing such that, apparently, we, I mean humanity, are living according to a very aggressive anthropogenic scenario. The rate of increase in CO₂ levels in the atmosphere is not decreasing; we have already exceeded pre-industrial levels of CO₂ in the atmosphere by one and a half times. Humanity has never lived with such concentrations of carbon dioxide. If this trend continues, the conditions of the Paris Agreement on climate change will be unachievable.

— Have we passed the point of no return? And if we have, what could that mean?

— I hope we haven't, but the problem is extremely serious. This can be understood by comparing three planets — Venus, Earth, and Mars. Cold Mars has practically lost its atmosphere, while Venus, whose atmosphere is primarily composed of CO₂ molecules, experiences a greenhouse effect with surface temperatures exceeding 400 ^оC. As a graduate student nearly half a century ago, I analyzed the sensitivity and stability of energy balance models of the Earth's climate under various types of impacts, including changes in solar radiation, CO₂ content, and aerosols in the atmosphere [1]. I also assessed the resilience of the Earth's climate system against a transition to a "snowball Earth" state.

— Snowball?

— Yes, the term snowball is used for that regime, which translates from English as "snowball." Prior to that, calculations using Budyko and Sellers-type energy balance models [2] estimated this resilience to be around 1% of the solar constant. I found that the resilience of the Earth system is significantly greater. Moreover, as cloud cover increases, the resilience increases. Nevertheless, the range of distances from the Sun that can support a habitable planetary climate is narrow. A little closer — you can burn, a little further — you can freeze.

— So we need to try to balance within our narrow range to avoid becoming Mars or Venus?

— The danger of a Venus-like scenario increases with ongoing anthropogenic warming.

— You graduated from PhysTech (MIPT) half a century ago, when the faculty was called "molecular-chemical physics," and there are many paths branching out from it. Yet you went straight into this current field. What motivated you?