Tipping Points to Vicious Circles, When We Cannot Control Temperature Rise
Torstai 5.12.2019 klo 15:23 - Mikko Nikinmaa
In the Eocene period about 50 million years ago, the mean temperature of the Earth was about 14oC higher than presently, and there was practically no ice anywhere. Further, the temperature gradient between poles and the tropics was small. This is taken by “climate deniers” to mean that human actions have little to do with temperature increase; “temperature increases as a result of natural causes”. Further, “climate deniers” maintain that human-like creatures were able to exist in Eocene conditions. Undoubtedly true, but at that time the number of human-like creatures was maximally a few million, and not more than seven billion. Close to half of the present human population lives in an area, which would be under the sea in ice-free world.
So, as a conclusion, there has been a markedly higher temperature on the earth because of natural causes, and some human-like creatures have survived it. However, this does not mean that mankind does not affect climate today, there is ample evidence on the contrary. At the worst, human actions can serve as trigger, causing a small temperature increase, which leads to tipping points with resulting vicious circles causing marked increases in temperature without any human role. Originally it was thought that the temperature rise before tipping points were likely to occur would be more than 5oC, then it decreased to 3-4 oC and the latest suggestion is that the probability for the occurrence of tipping points increases markedly, if the temperature increases 1.5-2 oC. The temperature has already increased by 1 oC from the preindustrial average, and the present promised actions to combat climate change would limit the temperature increase to approximately 3 oC. This is clearly larger temperature increase than what would be required for an increased probability for the tipping points and consecutive vicious circles of temperature increase to occur. Because of this, we have the CLIMATE EMERGENCY. Human actions matter now, but if enough of the tipping points have been reached, temperature increases no matter what we do. Below I list a couple of the tipping points with vicious circle properties, which may have been reached already.
Melting of Arctic sea ice. Recent years have seen open water in large areas of the Arctic sea. Virtually all the reports about it have been positive. Politicians have, e.g., rejoiced over the possibility of commercial shipping from Europe to Asia via the northeastern route. However, with melting sea ice one easily forgets that the white ice reflects virtually all the heat back to the sky, whereas the dark water absorbs the heat. This leads to marked acceleration of temperature increase.
Thawing of permafrost. Virtually all climate models have started with the outset that the thawing is gradual, and any effects reach significant level only a couple of hundred years from now. However, it has proven that the permafrost ice is a significant structural component of close to 20 % of the land area. Where this is the case, thawing permafrost is seen as huge craters etc. Where they occur, release of carbon (and methane) is much larger than estimated in the models. The carbon release can be double to what has been estimated.
Forest fires. The importance of forests as carbon dioxide sinks has repeatedly been emphasized. Whenever a forest burns, all the carbon it has accumulated is returned to atmosphere. Because of the hot and dry weather, the area affected by forest fires has increased markedly during recent years. In addition to forest fires, deforestation to gain agricultural land, and disease and harmul insect outbreaks especially in boreal forest decrease their carbon dioxide sink properties.
Aquatic pollution. For most of us it is unknown that about half of the Earth’s photosynthesis, i.e. carbon dioxide removal, is carried out by (mainly microscopic) algae. During recent years, the algal photosynthesis has been reduced by 10-20 % globally as the pollution of oceans has decreased the photosynthesis by algae.
Nitrous oxide production. The nitrogen fertilization, which is on the increase, increases the conversion of the fertilizers to nitrous oxide. This gas is the third most important greenhouse gas after carbon dioxide and methane. The need for nitrogen-containing fertilizers is on the increase as the fertility of agricultural land is decreasing.Two articles in Nature have aspects of what I have written above (Lenton et al. Nature 575: 592-595, 2019; Turetsky et al. Nature 569: 32-34, 2019).