**3. Climate change**

Climate change—in close connection with overpopulation, global species extinction and biodiversity crisis, and social crises—is the biggest challenge for mankind in our history. An adequate and stable global climate system is the most basic living condition of the biosphere, and as a part of it, human society and even all other living conditions are dependent on climate. This climatic system also determines the basic biogeographic patterns of our Earth. The fact and the anthropogenic origin of climate change are supported by evidence of a multitude of research findings and observations. With regard to these two things, there is an unprecedented degree of consensus in the scientific world.

In the background of this phenomenon, there are a lot of causes in strict connection with each other like overpopulation of mankind, the fossil fuel production and burning since the industrial revolution, the rapid eradication of forests and natural wetlands, industrial and transport pollution, unsustainable agricultural practices, and the rapid urbanization. Human activity is causing the greatest damage and dangers by breaking down the healthy functioning and regulatory capacity of the Earth's biosphere, eradicating primeval forests and rainforests, draining bogs and swamps, and reducing forest cover. The importance of grazing is also well known in the diversity of nature or near-nature grasslands [32].

There are a number of well-founded and less well-founded opinions about climate change today, but there are some important points that are beyond dispute:


Natural ecosystems provide carbon dioxide binding and storing functions, feedback processes, and in a number of direct and indirect ways regulate the climate in a biogeographical scale, and provide retention and dispensing of leaking residues, as well as the development of favorable micro- and mesoclimate. More recently, it has come to light that seaweeds emit dimethyl sulfide [33] and some pine trees emit terpenes from themselves [34, 47] as a result of rising temperature and carbon dioxide level; these can effectively promote cloud formation and so cool our planet. In addition, there are probably many ecological phenomena and processes so far unknown to science that have a prominent role in the biological regulation of climate [35] and which could also help the survival of the civilization of mankind if we understood and recognized them in time.

In the biogeographical research on global climate change, the following key issues can be identified:

