Breached! Six Of Nine Climate Boundaries That Keep Earth Habitable

The ‘planetary boundaries’ do not refer only to climate-change parameters, but also to a host of other interlinked biophysical and biochemical processes considered critical for supporting all life forms. These include processes like ocean acidification, ozone depletion, land use changes - specifically deforestation, and the accumulation of plastics or other synthetic waste. It places issues of climate change, biodiversity, desertification and pollution under one common framework.

 

The study, based on this broad framework, claims to present a more holistic understanding of the changes happening in crucial Earth-Ocean-Atmosphere interactions, and the impact of human activities in forcing these changes.

 

However, this method of assessing the health of the planet is relatively new and contested, hence not mainstreamed. A group of scientists, who have been working on this framework, published their first work in 2009, in which they identified the nine critical interconnected processes and defined their safety thresholds. Six years later, in their next major paper, they claimed that four out of the nine boundaries had been breached. The current paper, published in the journal Science, claims that six boundaries had been breached, and the first four had overstepped even further.

The interconnections between these processes and how human activities adversely impact them are all known to science. However, the scientific community is divided over the so-called safe limits set for each of these processes. Unlike global warming, where the raised safety threshold of carbon dioxide concentration at 450 ppm is now well accepted, from 400 ppm earlier, similar limits for land use changes or accumulation of synthetic waste are not clear as yet. There is also an argument that broad-basing threats like this could take the focus away from climate change, considered the most urgent, and spread the mitigation efforts very thin.

 

Something similar to the planetary boundaries framework exists within the climate change discourse as well. The extent of global warming is usually presented in terms of increases in carbon dioxide concentrations or the rise in average global temperatures. The impacts are often described in terms of sea-level rise, melting of glaciers, or increase in the frequency and intensity of extreme weather events like excessive rain, prolonged droughts or forest fires.

But a relatively novel approach has been a discussion on ‘tipping points’ - the thresholds for certain changes, which, when crossed, can become self-perpetuating and irreversible. Scientists have identified at least 15 such tipping points for processes like the disintegration of the Greenland ice sheet, spontaneous reduction in Amazon forest cover, or softening of permanently frozen grounds in the polar regions that have large amounts of carbon trapped in them.

Like a dam break, once such a breach happens, it reinforces the forces causing the breach, resulting in the breach getting bigger and bigger. Importantly, there is no opportunity for repair. It is a point of no return.

 

A study published last year suggested that a few tipping points, possibly five, might already have been reached even at current levels of temperature rise. For temperature rise between 1.5 degrees and 2 degrees Celsius, at least six tipping points become “likely” and four more become “possible”.

Even though the discussion on tipping points is slightly older than that on planetary boundaries, this framework too is not entirely uncontested. What does seem unequivocal, however, is that human activities are changing Earth systems rapidly and in unsustainable ways, which could make it harder for them to continue with their current living conditions.