The world seems to be getting hotter... How about holding a "sun umbrella" for the earth?

Excerpted from: Inside and Outside the Classroom Junior High School Edition·Science Youth August 2023 Weekly No. 3 (Total No. 1153) Text/Space Monk Editor/Shan Yu

The World Meteorological Organization predicts that global temperatures will continue to set new records in the next five years. The world seems to be getting hotter and hotter, and most of the heat on Earth comes from the sun. In order to cool down the Earth, can we block some of the sunlight? This "brain hole" seems crazy, but scientists have come up with a lot of strange ideas.

Option 1: Open an umbrella in the atmosphere

Volcanic eruption is an umbrella that nature gives to the earth
In 1991, Mount Pinatubo in the Philippines erupted, and the volcanic ash it ejected spread rapidly, covering the sky like a huge sun umbrella over the ground, greatly reducing the amount of sunlight reaching the surface and reflecting the energy of solar radiation back into space. This volcanic eruption unexpectedly caused the average temperature in the Northern Hemisphere to drop by about 0.5℃ in the following 15 months.

From 1906 to 2005, sulfate aerosols in the atmosphere caused the temperature near the surface to drop by 0.54-0.22℃.

During the same period, the emission of greenhouse gases such as carbon dioxide enhanced the warming effect of the atmosphere and the surface temperature rose by 0.87-1.22℃.

What's in volcanic ash?

The material ejected from the volcano contains a large amount of volatile substances such as sulfur dioxide. Sulfide rushes to an altitude of 20 kilometers and is oxidized into small sulfate particles, becoming a floating aerosol state.

That is to say, over the past 100 years, the aerosols injected into the stratosphere by large volcanic eruptions on Earth have partially offset the greenhouse effect during the same period. However, volcanic eruptions are occasional natural events and cause great disasters, so volcanic eruptions cannot be relied upon to achieve the goal of cooling the Earth.

Is it possible to artificially simulate the effects of a volcanic eruption?

Since aerosols can cool the atmosphere by blocking sunlight, can we artificially inject aerosols into the atmosphere?

As early as 2017, a research team at Harvard University launched a scientific research project to find out what effects and potential hazards would be produced by using high-altitude balloons to actively spread particulate matter into the stratosphere of the atmosphere. The most eye-catching one is the "solar geoengineering" initiated by the European Union. They envision using jet aircraft to spread a small amount of calcium carbonate or sulfate aerosol particles into the atmosphere at an altitude of about 20 kilometers above the ground, just like the haze produced by volcanic eruptions.

Solution Analysis

advantage:

•The cost of both aerosol particles and delivery vehicles is not high.

•Reaching the stratosphere is not difficult, takes little time, and takes effect quickly.

•It can be carried out over a specific area, and the particles will stay for a limited time and will not cause permanent obscuration.

shortcoming:

• Human manipulation to block sunlight may cause climate deterioration and change wind direction and rainfall.

•In areas blocked from the sun, crop yields may decline.

•Aerosol particles floating in the air may be inhaled into the lungs, posing a threat to human health.

Option 2: Open an umbrella in outer space

Even crazier than the Aerosol Project is the Earth Shield Project.
The so-called "Earth Shield Project" is to launch something similar to a shield into the universe, blocking the sun and the earth to reduce the sun's radiation on the earth.

Where should the Earth Shield be placed?

This shield must remain between the Earth and the Sun as the Earth revolves around the Sun, and remain relatively stationary with the Earth and the Sun. Astrophysicists have calculated that this shield can only be placed at a single location called the "Lagrange point L1." This point is located on the line connecting the Sun and the Earth, about 1.5 million kilometers away from the Earth.

At this point, the shield can automatically stay between the sun and the earth and revolve with the earth, almost without consuming any fuel, just like a parasol for the earth in space.

What will the shield block?

We don't need to block all sunlight, we only need to block part of it to keep the solar radiation received by the earth within a reasonable range. Considering that the shield is placed between the earth and the sun, the area it blocks should be near the equator, moving between the Tropic of Cancer and the Tropic of Capricorn as the sun's direct point moves.

How big does the shield need to be?

Assuming the shield is a circle, if we want to reduce the average surface temperature by 5°C, its diameter must reach more than 1,400 kilometers, which is equivalent to the distance from Harbin to Guangzhou. Its area will reach 6.5 million square kilometers, which is larger than half of China's land area.

How heavy is such a shield?

To transport such a huge man-made object into space, the most feasible way is to use the lightest and thinnest material to make it, but the light transmittance cannot be too high, otherwise the effect will be compromised. At the same time, this material must be able to withstand the extreme cold and high temperature of space, and will not deform under the attack of micrometeorites.

The structure used by the James Webb Telescope to shield the sun is a polyimide film as thick as a hair, with a coating of silicon and aluminum on it. Assuming that the Earth Shield also adopts a similar design, its mass will be at least 1,000 tons, equivalent to more than 160 Webb telescopes. It is an unimaginable huge project to launch such a behemoth to a distant Lagrange point and assemble it. This "brain hole" is very expensive.

Solution Analysis:

advantage:

•Once installed, the Earth Shield will be effective for a long time and will not require large-scale operations except for maintenance.

•The angles of the various reflective surfaces on the shield can be changed by remote control to actively adjust the sunlight reaching the earth.

shortcoming:

•To install such a huge project in space far away from the earth, the materials must be transported many times, the construction and launch costs are very high, and the subsequent maintenance is also very expensive.

•The project is very difficult to implement and no country can afford it alone. It requires international cooperation.

•The blocked sunlight will affect many areas of the Earth and may cause international disputes.

Think about this:

In the face of increasingly hot weather, do you have any creative cooling plans?