“It is very likely that human exposure has been the predominant cause of the observed warming since the mid-20th century,” the IPCC’s latest major climate study, AR5, published in 2013, concluded. Most likely, or extremely possible, means that it is at least 95 percent safe. The Climate Commission has never been clearer. The evidence that our greenhouse gas emissions warm 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 retains more heat
Greenhouse gases, such as carbon dioxide, methane and nitrous oxide, absorb certain parts of the earth’s heat radiation and then emit energy in all directions, even back to the earth. It warms the earth’s surface. Without greenhouse gases, the earth’s temperature would be -18 degrees. The same physics apply to other planets. Venus, which has a very dense atmosphere consisting of more than 96 percent carbon dioxide, has a temperature of about 470 degrees.
As early as 1896, Svante Arrhenius, a professor of physics, used basic physics to calculate what it would mean to increase the concentration of carbon dioxide in the atmosphere. His conclusion was that burning fossil fuels and other forms of combustion would cause the planet to warm. Svante Arrhenius later became Sweden’s first Nobel Prize winner when he received the Chemistry Prize in 1903.
Today, we emit the equivalent of 42 billion tonnes of carbon dioxide a year, and the concentration of carbon dioxide in the atmosphere has increased by more than 40 percent, from 280 parts per million in the early 1800s to about 410 now. It hasn’t been that high in over 800,000 years. As the atmosphere contains more carbon dioxide, more heat is retained and the earth becomes warmer according to basic physical processes.
2. Heating fingerprint: warmer closer to the ground, colder higher
Average air, land and sea temperatures are rising. If it were due to more energy coming from the sun, the whole atmosphere would heat up, from the earth’s surface and up to all the different layers of the atmosphere. If the heating is due to the heat that greenhouse gases keep from our emissions, the layers closest to the Earth would become warmer, while the stratosphere above would cool down. Researchers are seeing it right now. The atmosphere closest to the earth is warmer, and the higher it has become colder.
Since the 1970s, solar activity has also declined, while earth temperatures have risen. So the earth is heated by what is not the sun.
Warm-up fingerprint: Nights heat up faster than days
More greenhouse gases in the atmosphere retain more heat on the ground. A characteristic of such heating is that the nights heat up faster than the days. That is exactly what is happening. Over the last 50 years, nights with extreme cold have halved, while the number of extremely cold days has fallen by a quarter.
4. Heating fingerprint: emits less heat from the ground
Satellite measurements show that the earth emits less heat in space, and this applies to the parts of the heat radiation that are absorbed by carbon dioxide, methane and other greenhouse gases. Direct measurements also show that the heat radiation reaching the earth’s surface has increased since 2000 due to an increase in the concentration of carbon dioxide in the atmosphere.
5. Lighter fossil fuel carbon dioxide molecules are increasing
Scientists can find out where the increasing amount of carbon dioxide in the atmosphere occurs by examining the composition of 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 therefore they weigh differently – carbon-14 is the heaviest and carbon-12 is the lightest, but they work the same way in chemical reactions.
Carbon-14 is radioactive and decomposes with a half-life of slightly more than 5,500 years. Therefore, fossil fuels do not contain carbon-14, not carbon dioxide, which is produced by burning fossil fuels. Plants do not like to absorb carbon-13, so there is less carbon-13 in both carbon dioxide, for example from deforestation and forest fires, and fossil fuels, which are the remains of ancient plants. Carbon dioxide from the sea, as well as from animals and humans that breathe, has more carbon-13 and carbon-14, making it heavier.
The proportion of light carbon dioxide molecules in the atmosphere is constantly increasing. This shows that the growing amount of carbon dioxide comes from burning fossil fuels.
6. Traces of past climate change show that they are now ten times faster
Traces of how climate has changed over time 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 level of greenhouse gases in the atmosphere affects the climate. When the levels were low, the ground was colder and as the climate rose, the climate became warmer. As the climate changed rapidly, the effects on life on Earth became great, sometimes leading to the mass extinction of species.
Over the last 1.8 million years, the Earth’s climate has fluctuated between ice ages and warmer periods, as the Earth’s orbit and slope relative to the sun change in cycles. But such cycles are not behind the global warming we are now seeing. Instead, they would now lead to a stable temperature. This trend was interrupted by the Industrial Revolution in the 19th century, and now the average global temperature is rising instead of human greenhouse gas emissions.
It is not possible to explain the great climate change that we are seeing only by natural variations in solar activity, earth orbit and slope, or other natural processes. This is only possible if we include the impact of anthropogenic greenhouse gases. Now heating is also ten times faster than the ice age average.
Evidence from basic physics, from fingerprint warming, from the composition of carbon dioxide in the atmosphere and from what we have learned from past climate change, clearly shows that most climate change today is caused by us, especially through carbon dioxide emissions, and that it happens very fast.
Read more: 11 scientific answers to the favorite arguments of climate deniers