Thursday , January 20 2022

Here’s how we know it’s our emissions that affect the climate


“Human influence has probably been the main cause of the warming seen since the mid-20th century,” was the IPCC’s latest major compilation of climate research, AR5, which came in 2013. Most likely, or is highly likely, means it is at least 95 percent safe. The climate panel had never expressed itself more clearly. The evidence that our greenhouse gas emissions are warming the earth’s climate is very strong, and comes from many different sources. Here are some examples.

1. Basic physics: More carbon dioxide in the atmosphere holds more heat
Greenhouse gases, such as carbon dioxide, methane and nitrous oxide, absorb some parts of the heat radiation from the earth and then radiate the energy in all directions, even back to earth. It warms the surface of the earth. Without greenhouse gases, the earth would have a temperature of -18 degrees. The same physics also applies to other planets. On Venus, which has a very dense atmosphere containing more than 96 percent carbon dioxide, the temperature is around 470 degrees.

As early as 1896, professor of physics Svante Arrhenius, with the aid of basic physics, calculated what it would mean to increase the concentration of carbon dioxide in the atmosphere. He concluded that burning fossil fuels and other combustion would lead to warming of the entire planet. Svante Arrhenius later became Sweden’s first Nobel Laureate when he received the Chemistry Prize in 1903.

Svante Arrhenius.

Svante Arrhenius.

Photo: Ann Ronan Pictures

Today, we emit the equivalent of 42 billion tonnes of carbon dioxide a year, and the concentration of carbon dioxide in the atmosphere has risen by more than 40 percent, from 280 parts per million in the early 1800s to about 410 now. It hasn’t been so high in more than 800,000 years. With more carbon dioxide in the atmosphere, more heat is retained, and the earth heats up, according to basic physical processes.

2. Heat fingerprints: Warmer closer to the earth’s surface, colder higher up
Average temperatures in air, land and sea are rising. If it was because more energy came from the sun, the whole atmosphere would warm up, from the surface of the earth and all the way up through all the different layers of the atmosphere. If the heat is in place because heat is retained by greenhouse gases from our emissions, the layers closest to the earth would warm up while the stratosphere higher up would cool. That’s exactly what researchers are seeing now. The atmosphere closest to the earth is warmer, and upward it has become colder.

Since the 1970s, solar activity has also declined while ground temperatures have risen. So it’s something other than the sun that warms the earth.

Fingerprints of the warming: The nights are warming faster than the days
More greenhouse gases in the atmosphere keep more heat on the ground. A feature of such heating is that the nights get warmer faster than the days. That is exactly what is happening. Over the past 50 years, the number of nights with extreme cold has halved, while the number of extremely cold days has fallen by a quarter.

When the permanent ice melts, methane is released.

When the permanent ice melts, methane is released.

Photo: Science / TT Photo Library

4. Warming fingerprints: Less heat is radiated from the ground
Satellite measurements show that the earth radiates less heat into space, and that this applies to the exact parts of the heat radiation that carbon dioxide, methane and other greenhouse gases absorb. Direct measurements also show that the radiation of heat reaching the earth’s surface has increased since the year 2000, as the concentration of carbon dioxide in the atmosphere increases.

Illustration of the Adeos 2 satellite.

Illustration of the Adeos 2 satellite.

5. Lighter carbon dioxide molecules of fossil fuels are increasing
Scientists can find out where the increasing amount of carbon dioxide in the atmosphere comes from by examining the composition of the molecules in the gas. There are three variants of carbon atoms, carbon-12, carbon-13 and carbon-14. They have different numbers of neutrons in the atomic nucleus, and so they weigh different amounts – carbon-14 is heaviest and carbon-12 is lightest – but they work the same way in chemical reactions.

Carbon-14 is radioactive, and decomposes with a half-life of just over 5500 years. Therefore, there is no carbon-14 left in fossil fuels, and not in carbon dioxide that comes from burning fossil fuels. Plants do not like absorbing carbon-13, and so carbon-13 is reduced in carbon dioxide which, for example, comes from deforestation and forest fires and from fossil fuels, which are the remains of ancient plants. Carbon dioxide coming from the sea and from animals and humans that breathe has more carbon-13 and carbon-14, and is therefore heavier.

The proportion of light carbon dioxide molecules in the atmosphere is steadily increasing. This indicates that the increasing amount of carbon dioxide comes from burning fossil fuels.

6. Traces of previous climate change show that it is ten times faster now
Traces of how the climate has changed during history can be found everywhere on earth, such as in tree rings, seabed sediments, coral reefs and sedimentary rocks. Ice cores from Greenland, Antarctica and glaciers in the Andes, Himalayas and Kilimanjaro, among others, show that the levels of greenhouse gases in the atmosphere are affecting the climate. When the levels were low, the ground was colder and when they rose, the climate warmed. As the climate changes rapidly, the consequences for life on earth became large, sometimes with the consequent mass extinction of species.

The Earth’s climate has fluctuated between ice ages and warmer periods over the past 1.8 million years, as the Earth’s orbit and orientation relative to the sun vary in cycles. But such cycles are not behind the global warming we are seeing now. Instead, they would lead to a stable temperature now. The trend was broken by the industrial revolution in the 19th century, and the average earth temperature is now rising in line with human greenhouse gas emissions.

The great climate changes we see can only be explained by natural fluctuations in solar activity, orbit and earth’s slope or other natural processes. This is only possible if we include the effect of greenhouse gases from human activities. The heat now also goes about ten times faster than the average heat after an ice age.

The evidence of basic physics, of warming fingerprints, of the composition of carbon dioxide in the atmosphere, and of what we have learned from previous climate change clearly shows that we are human beings who cause ‘ Most of today’s climate change, especially through our carbon dioxide emissions, is going very fast.

Read more: 11 scientific answers to favorite climate deniers arguments

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