Na va-nad

This page dedicated to SRM (Solar Radiation Management)

A few starting points

• The 1991 eruption of Mount Pinatubo in the Philippines injected about 17 ± 2 million tons (≈ 17 Tg) of sulfur dioxide (SO₂) into the stratosphere, forming sulfate aerosols that spread globally within months. These aerosols increased the stratospheric optical depth to about 0.15–0.2, reflecting sunlight and causing a global mean surface cooling of roughly 0.4–0.6 °C over the following 1–2 years. Stratospheric aerosol concentrations gradually declined, returning to near-background levels by 1994, marking one of the clearest modern analogs for solar radiation management (SRM) effects.
• The IMO 2020 marine fuels regulation, which took effect on 1 January 2020, reduced the maximum sulfur content in ship fuel from 3.5% to 0.5% by mass, cutting global sulfur dioxide (SO₂) emissions from shipping by roughly 8–9 million tons per year. This sharp reduction diminished ship-track clouds—the bright, linear cloud formations induced by sulfate aerosols along major maritime routes—leading to measurably darker oceans and a decline in low-cloud reflectivity observed by satellites. Recent analyses suggest this loss of aerosol-induced cooling has increased global radiative forcing by about 0.1–0.3 W/m², likely contributing ~0.05–0.1 °C of additional global warming between 2020 and 2023.

In practice, human activity already constitutes large-scale, uncoordinated solar geoengineering, because every major source of emissions or land-use change alters Earth’s radiative balance. Burning fossil fuels releases CO₂, producing long-lived positive radiative forcing, while emitting or curbing sulfur oxides modulates short-lived negative forcing through aerosols that scatter sunlight. Even ordinary choices—flying and creating contrails, paving dark asphalt surfaces, or painting roofs white—collectively act as a patchwork of radiative interventions, unintentionally engineering the planet’s energy budget every day. We are all doing solar geoengineering every day.