Planetary Boundaries is a framework for expressing the resilience of the Earth as a system, and the
risk that human activities are destabilizing the system. The Earth
system has been remarkably stable for thousands of years. Losing that
stability would be very harmful to humans and society.
The diagram shows which Earth system processes are being pushed to dangerous
levels, and which processes are still at relatively "safe" levels with low
global risk.
Select a wedge to find out more about a process and how
we're monitoring it.
Find out more about the Planetary Boundaries framework through the
tabs above, and watch our introductory video.
Earth-system processes
Life on Earth is part of a huge system of processes and connections. Living
creatures affect each other and impact the chemistry and even the climate of
the world around them, and the effects go both ways in a great feedback
loop. Humans have the capacity to alter this entire Earth system through our
own activities. We also have the capacity to help maintain the Earth system
in a healthy state even as we grow and advance; to maintain it, we need to
monitor the system's "health". The Planetary Boundaries framework was
designed to help us do this.
The processes of the Earth system behave in ways that we can understand,
observe, and even predict. The Planetary Boundaries framework starts with
the physical, chemical, and biological processes by which we humans are
changing the Earth system.
Control variables
Each wedge in this diagram represents one of these processes. We monitor its
"status" using measurements such as concentrations or flow rates. These
measurements are called "control variables" because they
represent key aspects of the processes they're used to monitor.
Some processes are monitored using more than one control variable; for
example, the status of Biogeochemical
Flows uses both nitrogen flow and phosphorus flow.
The processes that make up the Earth system are tightly connected. This
means a change in one process will change other processes -- which will
in turn change the first process again, and so on.
All human activity will affect Earth system processes in some way.
Because the processes are so connected, if our activity changes them
too much, we risk destabilizing the entire Earth
system.
However, because we know how the Earth system has changed in the past and
we
can predict the impacts of what we do, we can figure out how much is
"too
much". Then we can set boundaries for ourselves to
maintain
the "health" of the Earth system. If a variable we're monitoring crosses
a
boundary, we know that process is at a high risk of
serious
problems on a global scale.
In the diagram, markers that are outside of the "safe limits" circle show
variables that have crossed a boundary.
A red marker ("definitely high risk") means the variable is so
far
past its boundary that we know the process can destabilize the
system.
An orange marker ("probably high risk") means the variable has
crossed its boundary and is likely to destabilize the system,
but
it might not be quite far enough yet to do that. This hopefully gives us
some warning.
A green marker ("low risk") means the variable has not crossed
the
boundary we have chosen, so that system is likely to remain stable. In
other
words, the Earth system and human society can likely adapt to any
changes
taking place and remain healthy overall.
The boundaries framework is very similar to the way we monitor our own
health. Think about having your blood pressure checked. There's a
"healthy
range" of blood pressure; if yours is outside of that range, you need to
find out what's causing it and (generally) do something about it. If
it's
outside of the healthy range by a lot, it's probably already
having
an impact on your health, and you need to fix the problem immediately or
risk serious consequences. If it's outside by only a little, it
might still be impacting your health, but it might not cause
any
further problems as long as you correct the cause soon.
The "boundary" for blood pressure is a value that medical professionals
have
chosen. It's chosen so that it's close to the levels where
serious
problems are likely, but far enough that it can act as a
warning
before things get bad.