A team of international scientists has published a study in” Proceedings of the National Academy of Sciences” (PNAS)showing that even if the carbon emissions are reduced and “Paris Agreement” are met, there is a risk of Earth entering into “Hothouse Earth” conditions.  A “Hothouse Earth” is a condition in which the global temperature will increase at an average of of 4-5°C  higher than pre-industrial temperatures with sea level 10-60 m higher than today.  

• “Human emissions of greenhouse gas are not the only factor that determine the temperature on Earth. The study put forward that human-induced global warming of 2°C may trigger other Earth system processes, often called “feedbacks,” that can force further warming — even if we stop emitting greenhouse gases,” “Avoiding this scenario requires a redirection of human actions from exploitation to taking care of the Earth system.”
• The study considers ten natural feedback processes, some of which are “tipping elements” that lead to rapid change if a critical threshold level is crossed. These feedbacks that stores carbon may emit it uncontrollably in a warmer world. These feedbacks are permafrost thaw, loss of methane hydrates from the ocean floor, weakening land and ocean carbon sinks, increasing bacterial respiration in the oceans, reduction of northern hemisphere snow cover, loss of Arctic summer sea ice, and reduction of Antarctic sea ice and polar ice sheets.
• These tipping elements can possibly act like a row of dominoes. Once one is pushed over, it pushes Earth towards another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over. Places on Earth will become uninhabitable if “Hothouse Earth” becomes the reality.
• The study shows how industrial-age greenhouse gas emissions force our climate, and ultimately the Earth system, out of balance. In particular the tipping elements in the planetary machinery, once a certain stress level has been passed, frequent changes fundamentally, rapidly and are perhaps irreversible. This flow of events may change the entire Earth system into a different mode of operation.

Reduction in greenhouse gases alone is inadequate

• The study says “to avoid “Hothouse Earth” it requires not only reduction of carbon dioxide and other greenhouse gas emissions but also improvement and creation of new biological carbon stores, for example, through improved forest, agricultural and soil management; biodiversity conservation; and technologies that remove carbon dioxide from the atmosphere and store it underground.
• Significantly, the study emphasizes that these measures must be underpinned by fundamental societal changes that are required to maintain a Balanced Earth where temperatures are approximately 2°C warmer than the pre-industrial temperature.
• It also says “Climate and other global changes show us that we humans are impacting the Earth system at the global level. This means that we as a global community can also manage our relationship with the system to influence future environmental conditions”.