Planetary boundries – The Green Tau

16th February

Of the seven planetary boundaries where we have passed from the safe zone into the unsustainable zone, the last I am writing about is climate change which is subdivided into CO2 concentration and radioactive forcing.

Radioactive forcing is a scientific concept which measures the imbalance between incoming and outgoing energy in Earth’s climate system. When energy from the sun reaches Earth, some reflects back to space while some gets absorbed. The difference between these two creates what scientists call radiative forcing, expressed in watts per square meter (W m⁻²). (1)

Different gases and particles suspended in the atmosphere (aerosols) plus the reflective capacity of the land/ sea surface contribute to this. Of all the gases in the atmosphere carbon dioxide has the greatest impact – absorbing energy (heat) whilst of aerosols sulphur dioxide has the biggest impact reflecting energy/ heat back out of the atmosphere. Thus the dirty smoke from coal power stations and from diesel shipping does in fact cool the planet, and as these sources of air pollution are reduced, there is an ironic increase in temperatures. Sulphur dioxide forms of smog which is harmful to health, often causing premature deaths (pictures of Delhi with obscured views of the city illustrate the density of these particles). (2)

“Scientists have proposed a PB for total anthropogenic radiative forcing at +1.0 W/m², relative to pre-industrial levels. This threshold is based on the climate system’s sensitivity to greenhouse gas forcing, observed responses of polar ice sheets to warming, and growing evidence of climate instability at forcing levels above +1.5 W/m². Exceeding this boundary increases the risk of irreversible climate impacts and long-term system feedback loops.” (3)

We exceeded this safe point in 1986.