Without Plants, a Red-Hot Earth Would Cook Under Billions of Tons of Carbon

The Earth is continuing to warm as environmental conditions shift and change. Greenhouse gas levels are increasing in our atmosphere, causing temperatures to rise. But how much worse would this warming be if we didn't have the benefit of plants to help capture carbon? It turns out that plants have been absorbing billions of tons of carbon, especially during the past 60 years, and that without them our planet would have transitioned to being red-hot.

From the 1860s to the 1950s, deforestation and logging were rampant. Land use by humans was a substantial source of carbon entering the atmosphere because of it. After the 1950s, though, humans began to use land differently and a botanical boom occurred. Plants overtook many environments that were previously cleared.

In fact, researchers found that since the mid-20^th century, the planet's land-based carbon "sink" has kept 186 billion to 192 billion tons of carbon out of the atmosphere. Had Earth's ecosystems remained a carbon source, though, they would have instead generated 65 to 82 billion tons of carbon in addition to the carbon that they would have not absorbed. That means a total of 251 billion to 274 billion addition tons of carbon would currently be in the atmosphere. This would have pushed current carbon dioxide concentrations to 485 parts-per-million (ppm), well past the accepted threshold of 450 ppm at which Earth's climate could drastically and irreversibly change.

"People always say we know carbon sinks are important for the climate," said Elena Shevliakova, one of the researchers, in a news release. "We actually for the first time have a number and we can say what that sink means for us now in terms of carbon savings. Changes in carbon dioxide emissions from land-use activities need to be carefully considered. Until recently, most studies would just take fossil-fuel emissions and land-use emissions from simple models, plug them in and not consider how managed lands such as recovering forests take up carbon."

The findings reveal exactly how important it is that plants be taken into account when it comes to calculating future warming. That said, if carbon dioxide levels do continue to increase, more vegetation will be needed into order to maintain the size of the carbon sink.

"A unique value of this study is that it simulates the past, for which, unlike the future, we have observations," said Scott Saleska, one of the researchers, in a news release. "Past observations about climate and carbon dioxide provide a test about how good the model simulation was. If it's right about the past, we should have more confidence in its ability to predict the future."

The findings are published in the journal Proceedings of the National Academy of Sciences.