Last year, the average global temperature rose by 1.5° C above pre-industrial levels, jeopardizing the goals of the Paris Climate Agreement. Global warming is a growing concern for climate scientists and researchers, who are calling for radical measures to bring the situation under control. Some proposed options seem threatening and a bit crazy, but scientists argue that there is no other way to resolve the situation.
Geoengineering
Geoengineering involves the use of technological solutions to influence the climate in order to reduce the temperature or change the amount of precipitation. In particular, the most well-known of the proposed methods is the spraying of aerosols that will scatter sunlight and reduce further heating of the atmosphere.
Among other things, researchers from University College London recently offered to use large aircraft such as Boeing 777F to inject sulfur dioxide into the stratosphere. Before that, the option of spraying sulfur dioxide over the tropics at an altitude of about 20 km was already proposed.
However, it turned out that current aircraft will not be able to do this, and it will be necessary to develop completely new ones, which may take many years. Based on the modeling results, the scientists found that injecting sulfur dioxide into the stratosphere can reduce the temperature on the planet by 0.6°C.
However, this should be done at an altitude of about 13 km near the poles. Why in the stratosphere? Because in the lower atmosphere, these aerosolized particles will be dispersed by clouds and fall out as rain.
The stratosphere, on the other hand, remains dry and free of clouds, so aerosols can stay there for months, maybe even years, depending on the height from which they are sprayed. Researchers from University College London have calculated that in order to effectively cool the planet, it will be necessary to inject 12 million metric tons of sulfur dioxide per year at an altitude of 13 km in spring and summer. This is for each hemisphere.
However, this approach has significant drawbacks. First, there is the risk of acid rain. On the other hand, no one knows for sure how these aerosol particles will behave in the stratosphere in interaction with other anthropogenic substances and greenhouse gases.
In addition, such artificial cooling of the planet can lead to significant falling yields and provoke a food crisis in many poor and developing countries. If such spraying is carried out exclusively in the Southern Hemisphere, it will provoke an increase in the number of tropical cyclones, and if — only in the Northern Hemisphere — it will reduce the number of tropical cyclones, but will cause record drought in Africa.
According to some estimates, the spraying of sulfate aerosols can lead to unpredictable consequences, including more rapid warming of the world’s oceans. In addition, the large-scale implementation of such a project will require funding in the amount of at least several billion dollars annually for at least 15 consecutive years.
Another option would be to spray sea salt aerosols, where the salt would act as nuclei around which water droplets would condense in clouds. Such clouds would retain more moisture and reflect sunlight better by forming smaller droplets.
In one of the research scientists confirm that aerosols actually have a much stronger effect on cloud reflectivity than was thought. In order to get salt particles into the clouds, it is proposed to inject aerosols into the layers of marine clouds by spraying seawater using nozzles capable of converting salt water into small particles.
A significant advantage of this process may be the possibility of more significant cooling of the poles compared to the tropics, which will slow down the melting of ice. This process does not require toxic chemicals and is affordable and feasible. However, the use of sea salt aerosols will lead to a reduction in precipitation and could have a catastrophic impact on the climate in certain regions
The startup has conducted trial launches of spray balloons in Mexico. Among other things, the startup collects donations from those willing to help cool the planet and even offers flights on such balloons and direct participation in the spraying process.
Many scientists and environmentalists have criticized this project, calling it premature and ill-conceived, and one that could lead to unexpected consequences. However, the startup’s founder, Luke Eisman, plans to increase the amount of sulfur dioxide released into the stratosphere and also wants to equip the balloons with telemetry equipment and other sensors to determine their effectiveness.
CO₂ capture
Carbon capture involves removing carbon from emissions from industrial plants, such as power plants, oil refineries, and others, in several ways. For example, coal, waste, and other biomass can be converted into synthesis gas and then separated from CO₂.
By absorption with a solvent, or adsorption or membrane separation of CO2is separated from hydrogen. The purified hydrogen is burned to produce energy, while the CO2 emitted in the previous step is captured and can be safely buried or used in other industrial processes. Such technologies may not be cheap and require equipment upgrades, but they offer more efficient carbon capture than capture from fossil fuel emissions.
Another way is to capture CO₂ from the smoke generated during the fuel combustion process. CO₂is separated from the flue gas, usually using solvents such as amines, compressed and transported to a storage facility. Carbon is mainly stored in the following geological formations, salt deposits or depleted oil and gas fields. Carbon dioxide is often used for injection under pressure into oil reservoirs to remove sediments from aging oil fields and extract oil that would otherwise be unavailable.
Another option is to burn the fuel in pure oxygen. This produces a highly concentrated CO₂ stream that is easier to capture and store This results in the formation of mainly CO₂ and water vapor The water vapor condenses, leaving a concentrated stream of CO₂.
In particular, the latest achievements that deserve attention include the sodium-air fuel cell, created by researchers from the Massachusetts Institute of Technology (MIT). Scientists have achieved a higher energy density in an electric battery by replacing a liquid electrolyte with a solid fuel cell.
As part of the experiment, they used two vertical glass tubes that were connected in the middle with a solid ceramic electrolyte and a porous air electrode. One of the tubes contained a liquidsodium, and in the other — air.
The chemical reaction produced sodium oxide and energy. By controlling the humidity of the airflow, the scientists successfully generated 1700 W⋅h per kilogram of each battery. This could be a promising solution for heavy electric vehicles such as aeroplanes and ships. Most importantly, the sodium oxide released by the fuel cell reacts with moist air to form sodium hydroxide. The latter reacts with carbon dioxide to form sodium carbonate, and then — sodium bicarbonate, or baking soda. In addition to cleaning the atmosphere of CO₂, sodium bicarbonate can enter the oceans and reduce their acidification.
However, researchers from the University of Michigan, led by chemist Charles McCrory together with the laboratory Jesus Velazquez at the University of California and Anastasia Aleksandrova’s lab at the University of California, Los Angeles, have developed a new method of CO2 capture. Their subsequent conversion into metal oxalates. These can be used as precursors for cement production.
The researchers note that One of the types of materials that can be used as an alternative cement precursor is metal oxalates, simple salts.
The scientists add that lead can be used as a catalyst to facilitate chemical reactions to convert CO₂for metal oxalates. However, this requires a large amount of lead catalysts, which is dangerous for the environment and human health.
In their work, the researchers used polymers, reducing the required amount of lead to one part per billion. In order to obtain oxalates, scientists use a set of electrodes.
On one of them, CO₂is converted to oxalate. The other metal electrode is oxidized and releases metal ions, which bind to the oxalate ions and precipitate it from the solution as solid metal oxalate. McCrory claims that once carbon dioxide is converted to solid metal oxalate, it will not re-enter the atmosphere under normal conditions.
At the same time, scientists at the University of Cambridge have developed a solar-powered reactor that captures CO₂ directly from the air, converting it into synthesis gas. Unlike traditional methods of capturing CO₂ and storing it deep underground, the new reactor is powered exclusively by solar energy and offers an environmentally friendly and profitable alternative.
The reactor consists of a system with special filters that capture CO₂ from the air at night. During the day, sunlight heats the captured carbon dioxide by absorbing infrared radiation. At the same time the semiconductor powder absorbs ultraviolet radiation, triggering a chemical reaction that converts CO₂ into a mixture of hydrogen and carbon monoxide.
Conclusions
These are just a few examples of promising developments that can be scaled up to capture CO₂ efficiently. Some scientists also propose enhancing the photosynthesis of plants such as rice, wheat, cotton, and trees to capture CO₂ more efficiently and bury it in the ground Among other things, enhanced photosynthesis can slow down the rate of ocean acidification.
Today, CO₂ capture and its further use as a raw material, rather than just burial and storage, looks most promising if the relevant technologies are scaled up.
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