The most correct and safe way of fixing climate is the reduction of greenhouse gas emissions than, in fact, humanity and employ now. According to the Paris climate agreement, adopted December 12, 2015, in order to avoid catastrophic changes, we need to stop the increase in global temperatures on Earth within 2 degrees (the guides are the levels before the industrial revolution), it is still better to stay within 1.5 degrees.
But the new US President Donald trump was determined to fulfill his campaign promise by declaring June 1 of withdrawal from the Paris agreement. In his opinion, the fight against global warming portends for America's loss of millions of jobs and billions of dollars. It is possible that other countries will relate to the assumed obligations carelessly. However, even if each country put its signature in Paris, the emissions will actually be reduced, this does not lead to the return temperature to the previous level — our world is too hot.
Therefore, in addition to the Paris agreement on reducing greenhouse gas emissions, scientists consider different variants of the radical counter-warming. So, the radiative balance of the Earth can in the future affect using geoengineering methods. However, many climate scientists and experts in climate policy have avoided the term, because talk about the large-scale intervention in nature can harm the reputation of a specialist in this area.
Geoengineering strategies fall into two categories: the removal of accumulated carbon dioxide from the atmosphere and reducing the heat generated by the planet. The first is more desirable, but very expensive, energy-intensive and very problematic from a technological point of view. For example, we can talk about the restoration of the forests that covered almost half of the total land area on the planet. Obviously, this is unrealistic. The alternative technology of direct extraction from the atmosphere of carbon with subsequent disposal or use — despite all the hype, are still in their infancy.
So a more realistic currently, it seems the change in the thermal balance without decreasing the CO2 concentration.
To do this, or to block incoming sunlight before it enters the Earth's atmosphere, or to radiate more heat back into the space.
In the first article of Science Ulrike Niemeyer from the German Meteorological Institute of the max Planck Society in Hamburg and Simon Tilmes from the laboratory of atmospheric chemistry, observations and modeling at the us National center for atmospheric research (towards) in boulder consider the pros and cons of the systematic introduction into the stratosphere large amounts of sulphur.
This method is called modification of the stratospheric aerosol layer (SAM).
Naturally this happens at the moments of largest volcanic eruptions. Particles of sulfur dioxide into the stratosphere, is able at some time to cause a global cooling of the planet. Thus, the eruption of the Philippine volcano Pinatubo in June 1991 resulted in the release of about 17 kilotons of sulfur dioxide and,
accordingly, cooling of the Northern hemisphere by 0.5–0.6 degrees.
In contrast to extraction of carbon, sulfur spraying to organize not difficult. Main for this are already there — high-altitude aircraft, capable of delivering a capacity of sulfur into the stratosphere. Difficulties arise in assessing the scale at which it is possible to obtain significant cooling. Niemeyer and her co-author believe that for cooling of 1 degree will need 6700 flights per day.
According to the models, the widespread use of the SAM can be used to significantly mitigate the changes that are now taking place due to greenhouse gases and lead to a rise in global temperatures and precipitation extreme precipitation.
Expected side effects include a slowing of the hydrological cycle. This may affect the availability of fresh water and lead to reduced monsoon precipitation. The authors caution that while the scope of the "injection" of sulfur to achieve the desired level of cooling of the planet is difficult to determine, because, depending on the models there are very large variations. Remain uncertain and technological requirements, difficult to estimate economic costs and SAM.
According to a rough estimation, if the active struggle with the consequences of global warming (supported by the same large-scale catching and removing carbon from the atmosphere) starts in 2040,
to keep the temperature within 2 degrees in the stratosphere will have to spray sulfur for over 160 years. The cost of implementing such projects to $20 billion a year.
The second article is written by Ulrika Lohmann and Blazem Gasparini from the Swiss Institute for atmospheric and climate science ETH in Zurich, devoted to ways to manipulate the clouds so that they are less absorbed outgoing long-wave radiation from the Earth's surface. Semi-transparent thin Cirrus clouds at high altitudes can absorb long-wave radiation, creating a heating effect. The researchers used a special model to explore the possibilities of the destruction or the creation of artificial Cirrus clouds that absorb less heat.
All this should be done with the use of pellets-germ, concentrating moisture, for example, by scattering of ice crystals.
Here, too, will involve high-altitude aircraft. The authors note a number of obstacles on the way of wide use of this approach, including the possible destruction of the ozone layer and intensification of tropical convection. The conclusion is that if the technology to create artificial Cirrus clouds do not work carefully enough, the effect may be the opposite — instead of the intended cooling we will get more warming.
"Cirrus clouds formed at high altitudes, absorb part of the radiation which otherwise would be lost to space. In this sense, they act like greenhouse gases," explains Ulrike Lohmann in an interview with IBTimes.
Cirrus clouds consist mainly of ice crystals. To prevent their formation, it is necessary to seed the atmosphere with tiny particles such as dust from deserts or pollen. These particles become the centers of formation of larger ice crystals with simultaneous reduction of their number. "This prevents the scattering of sunlight, and allows more longwave radiation to escape into space," says Lohmann.
Sending large numbers of aircraft to fight the clouds — idea expensive. However, Lohmann indicates that it is probably the best option of geoengineering projects. In addition, large ice crystals absorb more water vapor present in the upper atmosphere. "Since water vapor is also a greenhouse gas, reducing its concentration in the upper troposphere contributes to the warming effect," she said.
What can go wrong with such projects? Too many unknown factors. The cooling of the planet could trigger a new quirks in the weather around the world. You can destroy the system of the annual Indian monsoon. Rose of the winds on the earth can completely change. In addition, the need to continue implementing these projects for a very long time — carbon dioxide is still in the atmosphere and conducts "subversive activities". In addition, continue poisoning, "acidification" of the ocean.
However, the technical challenges of geoengineering pales in comparison to the challenges faced by governments when making decisions on implementation of these technologies. Most disturbing is the possibility that some desperate country, group of countries or just a very rich man decides to take independent steps in this area.
"Imagine that someone will have to fly in the atmosphere with sulfur spray, and then a delayed monsoon season in India. Break out of the geopolitical crisis!" — said Janos Pasztor, Executive Director of the Initiatives for managing climate and geological research Council, the Carnegie, co-author of another article, which deals with the policy implications of the above experiments.
Decision-making should be preceded by the international dialogue with the participation of an increasing number of countries. Setting the "global thermostat" will need careful monitoring, and no one knows how all this will be difficult.
So there is also a local and regional risk: what happens if one part of the world will experience more side effects from geoengineering activities than any other? There is such a thing as "effect of termination" (similar to the abstinence syndrome in medicine): after the start of the activities you can't stop. "If you stop, the temperature will return to the previous level, and it will be a disaster," said Pasztor. And most importantly, how to conduct research on geoengineering? Will have to use the entire Earth as a laboratory.
"I want to emphasize that we do not promote geoengineering, we promote the idea of dialogue," says Pasztor. The lack of critical data makes many scientists nervous about such projects. In an editorial in Wired magazine says: "the World is moving towards an increasingly risky future and not ready to solve institutional and administrative problems associated with these technologies. Geoengineering carries consequences for the entire planet and therefore should be discussed by national governments in intergovernmental institutions, including the UN."
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