The atmosphere—that is, the layer of gases surrounding the Earth—makes life on our planet possible. At the same time, its composition is significantly influenced by that very life. It has undergone dramatic changes time and again throughout the various geological eras. Water vapor and, above all, the trace gases carbon dioxide, methane, and nitrous oxide in the atmosphere trap some of the energy radiating toward Earth, causing the planet to absorb more heat than it radiates. This natural greenhouse effect is what makes our current way of life possible. Without it, the global average temperature would be -18 degrees Celsius instead of +15 degrees. [23]
If we humans release more greenhouse gases—especially CO₂—into the atmosphere than natural processes do, we thereby raise the Earth’s temperature. But how do we humans do this? To understand this, let’s take a closer look at carbon, which is found in all living things. It combines with oxygen to form CO₂ in the atmosphere. During photosynthesis, plants use solar energy to take in CO₂ and, together with water, convert it into sugar, which they then use to form leaves, stems, roots, and other organic matter. They exhale the oxygen. All animals, fungi, microorganisms, and even we humans are thus nourished by plant photosynthesis.
Plants thus remove carbon from the atmosphere. Part of this carbon returns to the cycle when microorganisms break down plant matter back into CO₂ or when wood burns. Another part is permanently stored in the soil and on the ocean floor.
For millennia, the carbon cycle remained relatively stable until, a good 200 years ago, humans began extracting and burning fossil fuels—that is, carbon stored in the earth, such as oil, coal, and natural gas—in ever-increasing quantities. At the same time, we are reducing carbon storage in trees and the soil by converting forests, wetlands, and grasslands into farmland, urban areas, and deserts.
Approximately 40 percent of all additional greenhouse gas emissions caused by humans are directly or indirectly attributable to our diet and agricultural production—from deforestation to the use of chemicals and machinery in cultivation, through drying, transportation, refrigeration, heating, packaging, all the way to the destruction and disposal of food. [24] Methane (digestive gas from ruminants and wet rice paddies) and nitrous oxide (from fertilizers)—gases with extremely high global warming potential—play a particularly significant role in agriculture. We will only achieve the goal of the Climate Convention—to limit global warming to 1.5 degrees Celsius as much as possible—if we reduce these additional emissions by nearly 90 percent by 2050. [24] This is an enormous challenge.
Different foods generate varying amounts of emissions from farm to plate and to the landfill. Meat and dairy products have a high greenhouse gas footprint because each calorie of animal-based products requires many times more plant-based calories to produce, and methane is released in the process. Meat and milk from cows grazing on local pastures are better for our climate than those from animals fed soy from Brazil. A strawberry that’s flown halfway around the world is significantly more harmful to the climate than a locally grown strawberry—unless it comes from an oil-heated greenhouse. The energy required for freezing and heating during processing also plays an important role.
