UN Global report_2019

Box 1-5
Tipping points
A tipping point is a critical point in an Earth system component, around which small perturbations can
trigger an irreversible transition from one stable state to another. Transitions are not necessarily abrupt; but
once begun can be impossible to reverse, and the eventual change is very dramatic. It is believed that such
points exist for many components of the Earth system – such as the Arctic summer sea ice, the Greenland
and Antarctic ice sheets, and the Amazon rainforest.
The dynamics can be illustrated by the Arctic summer sea ice, which is currently melting fast due to climate
change. As the ice melts, more of the ocean area becomes darker and so absorbs more sunlight, which
increases global warming and speeds up the melting. As a result, the Arctic is warming much faster than
the rest of the world. The tipping point for the Arctic sea ice will be the critical temperature, after which the
melting will become rapid and irreversible. Some estimate that it will take just 10 years for the ice to melt
completely after the tipping point is reached.
The increase in greenhouse gases in the atmosphere and warming causing the melting of the Arctic sea ice
may also have complex impacts on other systems, for example, the release of methane due to melting of
permafrost will further exacerbate climate change; melting of the Greenland ice sheet; ocean circulation
changes; ocean acidification; extreme weather events; and accelerated biodiversity loss.
Each of those impacts can lead to transitions in other components of the Earth system, in vicious feedback
loops that would lead, through a cascade of transitions, to radically different states for many components.
Those transitions would be irreversible on the time scales relevant for society. The exact point at which such
transitions can be precipitated is difficult to estimate, but they are believed to be likely under many different
scenarios.
The Earth system could likely be kept in its current state by actions such as reducing greenhouse gas
emissions and strengthening carbon sinks to achieve net-zero emissions. However, the time window within
which such actions need to occur could be a short one. 48
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1.2.2. Regions and population groups
Individual countries, as well as their groupings along
regional or other parameters, can differ significantly
in the challenges they face toward achieving the
Sustainable Development Goals. Those challenges
will only be described very briefly in this Report; more
detailed treatments are available in regional Sustainable
Development Goals reports and the voluntary national
reviews.
See for example the special challenges faced by small
island developing States (box 1-6) and least developed
countries (box 1-7). 484950
The transformative power of sustainable development