Climatologists have shown that at the current level of the average annual temperature of the atmosphere, the volume of glaciers is very far from the steady state. This means that artificial measures to reduce greenhouse gas emissions will not stop the melting of glaciers, but will only slow it down a little, scientists write in the Nature Climate Change .
As a result of global warming, the average sea level is steadily increasing. The main contribution to this process has two factors: first, the thermal expansion of water in the ocean, and secondly, the melting of ice in the polar ice sheets and in the highland glaciers. Since the very global changes in climate and their direct consequences (including sea level rise) have a negative impact on both humans and natural ecosystems, the UN Framework Convention on Climate Change was signed to slow it down, which limits the maximum level of emissions greenhouse gases. However, despite the fact that the increase in the concentration of greenhouse gases in the atmosphere is called one of the main causes of warming, the possible effectiveness of these measures so far raises questions.
To assess how reducing greenhouse gas emissions can affect the change in the rate of melting of polar glaciers on Earth and what additional measures may be worth taking, climatologists from Germany and Austria, led by Ben Marzeion from Bremen University, computer simulated the melting of the Antarctic and the Greenland ice sheets at various temperatures of the Earth’s atmosphere.
Scientists note that the dynamics of the melting of ice sheets has two characteristic time scales. On the time intervals of several millennia, the rate of melting of ice is determined, first of all, by the interaction of the glacier with that part of the land on which it is located. In shorter time intervals – several hundred years – the dynamics of shrinking the volume of the glacier is more dependent on the interaction with the surrounding glacier atmosphere. Due to the feedback system that arises between the volume of the glacier and the air temperature for each state of the atmosphere, there is a corresponding stable volume of the ice shield. The rate of melting depends on how far the glacier is at a given time from the equilibrium state.
To assess how far from the steady state at the current air temperature are now the polar ice shields, scientists have simulated the equilibrium states of glaciers at different average temperatures of the atmosphere. For modeling, one of the most accurate modern climate models CMIP5 was used, with the help of which it is possible to relate the temperature of the atmosphere to the level of precipitation.
It turned out that at the current temperature, the current mass of ice shields is very far from a sustainable level. The deviation from the equilibrium mass of the glacier is now about 36 percent. Thus, even if the temperature of the atmosphere is maintained at the current level, when the glacier reaches a stable volume, the world ocean level will rise by 10 centimeters. In order to make the glacier stable with the current mass, the temperature and concentration of carbon dioxide in the pre-industrial level (about the middle of the 19th century) are needed.Nevertheless, according to scientists, during the 21st century a stable level of mass of glaciers will not be achieved. Therefore, in order to assess the possible change in the volume of ice over the next several decades, depending on the dynamics of the atmosphere temperature, the scientists conducted dynamic modeling of glaciers taking into account several scenarios of greenhouse gas emissions. It turned out that the difference in sea level rise between different emission scenarios is insignificant and is about 10 centimeters by the end of the 21st century. At the same time, at least some statistically significant difference in the implementation of various scenarios appears only after 2080.
Climatologists note that the results of the simulation show that artificial reduction of emissions in any case will not stop the melting of glaciers, and can only slightly change its speed. Nevertheless, according to the authors of the paper, the results obtained relate primarily to short time intervals (on the order of several decades), for longer periods, measures to reduce the rate of melting of glaciers may prove more effective.
A large number of studies have been devoted to studying the mechanisms of thawing of the Antarctic glaciers, which are carried out both with the help of computer modeling and on the basis of geological data. For example, as a result of one such study, scientists have established that the melting of glacier marine areas can affect the movement of ice on the continent within a radius of up to 900 kilometers from the melting point. And another group of scientists showed that not only the shelf ice glaciers of western Antarctica, but also the ice on the eastern part of the continent, play an active role in melting the Antarctic ice sheet.