Papers = Ideas and Notes

Rockstorm paper

Summary:

  • A new approach has been proposed for defining preconditions
  • Crossing certain biophysical thresholds could have disastrous consequences for humanity
  • 3 of 9 interlinked planetary boundaries have already been overstepped

Introduction:

  • The stability of the planet's environment is under threat.
  • Humans actions have become the main driver of global environmental change
  • Human activity could see the Earth's system pushed outside a stable environment state
  • Before the threat of human activity, environmental change occurred naturally and Earth's regulatory capacity maintained the conditions
  • Regular temps, freshwater availability and biogeochemical flows all stayed within a relatively narrow range
  • Due to reliance on fossil fuels and industrialised forms of agriculture, human activities have reached a level that could damage the systems

Planetary boundaries

Proposed framework based of the planetary boundaries

These define the safe operating space for humanity with respect to the earth system and biophysical processes

Scientists have tried to identify the Earth-system processes and associated thresholds which, if crossed, could generate unacceptable environmental change.

Nine Processes:

  1. Climate Change
  2. Rate of Biodiversity loss
  3. Interference with the nitrogen and phosphorous cycles
  4. Stratospheric ozone depletion
  5. Ocean acidification
  6. Global freshwater use
  7. Change in water use
  8. Chemical pollution
  9. Aerosol loaiding

Climate Change

International discussions on targets for climate mitigation have intensified.

There is a growing convergence towards a ‘2 °C guardrail’
approach, that is, containing the rise in
global mean temperature to no more than 2 °C
above the pre-industrial level.

Boundary based on two thresholds. Atmospheric conc. of CO2 and radiative forcing

We propose that human changes to
atmospheric CO2 concentrations should not
exceed 350 parts per million by volume, and
that radiative forcing should not exceed 1 watt per square metre above pre-industrial levels.

Transgressing these boundaries will increase
the risk of irreversible climate change, such as
the loss of major ice sheets, accelerated sealevel
rise and abrupt shifts in forest and agricultural
systems

Three reasons for proposed climate boundary

  1. Current models may significantly underestimate the severity of long term climate change for a given conc. of greenhouse gases

Models do not include the long-term reinforcing feedback processes that further warm the climate, such as decreases in the surface area of ice cover or changes in the distribution of vegetation

Thus why they have taken these feedback processes into consideration

  1. Stability of large polar ice sheets

CO2 concentrations were a major factor in the
long-term cooling of the past 50 million years.

Moreover, the planet was largely ice-free until
CO2 concentrations fell below 450 p.p.m.v.
(±100 p.p.m.v.), suggesting that there is a critical threshold between 350 and 550 p.p.m.v.

we are beginning to see evidence that
some of Earth’s subsystems are already moving
outside their stable Holocene state. This
includes the rapid retreat of the summer sea
ice in the Arctic ocean, the retreat of mountain
glaciers around the world, the loss of
mass from the Greenland and West Antarctic
ice sheets and the accelerating rates of sealevel
rise during the past 10–15 years

  1. Earths subsystems are already moving outside the stable state

Rate of Biodiversity loss