27.12.2019 |

Interactions between planetary boundaries amplify human impact on Earth

Planetary boundaries (based on Steffen et al.)

In 2009, a group of scientists proposed the planetary boundaries concept, identifying nine processes that regulate the stability and resilience of the Earth system. Crossing these boundaries increases the risk of generating large-scale abrupt or irreversible environmental changes, they warned. In an update of the framework, the scientists argued that the safe operating space for four of the nine systems has already been clearly exceeded, namely in the area of climate change, land-system change, human interference with the biogeochemical cycles (phosphorus and nitrogen) and, in particular, the loss of biosphere integrity (biodiversity loss and species extinctions). Now a new study, published in the journal “Nature Sustainability” on December 16, shows that transgressing one planetary boundary can also amplify human impacts on another one. “We found a dense network of interactions between the planetary boundaries,” said Johan Rockström, co-author of the study. According to the scientists, two core boundaries – climate change and biosphere integrity – contribute more than half the combined strengths of all the interactions in that network. “This highlights how careful we should be in destabilizing these two,” Rockström added.

The scientists quantified interactions between the Earth system processes represented by the planetary boundaries. They concluded that biophysical interactions have in fact almost doubled direct human impacts on the nine planetary boundaries. One example for how human impacts on the Earth system are amplified is the interconnection between deforestation and climate change. Burning down tropical forests to expand agricultural lands increases the amount of CO2 in the atmosphere. The additional greenhouse gases then contribute to global warming – harming the forests thus also affects climate stability. The temperature increase can in turn further enhance stress on tropical forests, with negative consequences for agriculture. The resulting amplification of effects is substantial. But the situation could even get worse since the study does not yet take tipping points into account. Beyond a certain threshold, for instance, the Amazon rainforest might show rapid, non-linear change. Such a tipping behaviour would come on top of the amplification analysed in the study.

Another distressing example of connections between global environmental problems that amplify human impacts on the Earth System are the disastrous bushfires which are currently raging across eastern Australia “Climate change, through increasing temperatures and changing rainfall patterns, has played a significant role in creating the conditions conducive for such massive and widespread fires,” said lead author Dr Steven Lade from The Australian National University (ANU). “In turn, the bushfires are having an impact on the climate system by releasing large amounts of carbon dioxide into the atmosphere, contributing to further climate change in what scientists call a 'feedback loop'.” He also points to the fact that smoke, unlike some other types of aerosols, also absorbs solar radiation, accelerating climate change even further. “The severity of the fires coupled with ongoing climate change could lead to ecosystem shifts as the landscape eventually recovers,” Dr Lade warns. “If new ecosystems store less carbon than the forests that were burnt, a long-term, net increase of carbon dioxide in the atmosphere will occur.”

“Our results show that an integrated understanding of Earth system dynamics is critical to navigating towards a sustainable future,” the authors write. They express the hope that their insights will now be applied in policy design for safeguarding the livelihoods of generations to come. “We offer our survey of planetary boundary interactions to policymakers and the scientific community,” they conclude, “as a summary of current scientific knowledge, a call for future research to better characterize interactions and as a framework to prompt policy discussions and planning towards a sustainable future.” Rockström highlights that there is good news for policy-makers in the study’s findings. “If we reduce our pressure on one planetary boundary, this will in many cases also lessen the pressure on other planetary boundaries. Sustainable solutions amplify their effects – this can be a real win-win.” (ab)

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