The Earth’s oceans are teeming with tiny plant plankton, and when zooplankton feed on them, they release a chemical called dimethyl sulfide (DMS). This chemical is responsible for the distinctive ‘smell of the sea.’ In the atmosphere, DMS reacts to form sulfur-containing particles that act as nucleation sites for water vapor to condense on, eventually forming clouds. Clouds, in turn, influence local weather patterns and the global climate by reflecting sunlight back into space.
Other tiny particles also exert significant effects on the environment. Sulfur emissions from ship funnels can form cloud-seeding particles, creating the visible ‘shiptracks’ seen in satellite images. Conversely, soot from burning fossil fuels absorbs solar energy, warming the surrounding air and inhibiting cloud formation.
Sulfur particles can also reach high altitudes in the atmosphere, forming a haze that blocks sunlight from reaching Earth’s surface. Despite understanding these processes in general terms, quantifying their precise effects has been challenging.
The behavior of aerosols remains a major source of uncertainty in climate models, contributing to the error bars in projections of future global temperatures. To address this challenge, NASA launched the PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite into Earth’s orbit on February 8th, 2023.
PACE’s cameras will scan the planet every one to two days, creating a comprehensive census of tiny particles suspended in the oceans (plankton) and the air (aerosols). Its main camera can detect light across a wide spectrum, allowing it to distinguish between different types of phytoplankton, a crucial distinction as diatoms support fisheries while cyanobacteria can be harmful.
Two additional instruments on PACE will provide data on aerosol size and shape, enabling researchers to differentiate between soot, sea spray, and fossil fuel combustion particles for the first time. Climate scientist Gavin Schmidt emphasizes the transformative potential of this data for climate models, which currently rely on assumptions to fill the gaps in existing aerosol data.
Improved aerosol data will also inform our understanding of the impact of air pollution on climate change. Regulations in Europe and North America have reduced air pollution from fossil fuels since the 1980s, benefiting human health. However, this has also lifted a veil of smog, revealing the warming effects of greenhouse gas emissions that were previously masked.
Cleaning up air pollution could significantly influence the climate in the coming decades, and better data will enable more accurate modeling of these effects. Similarly, climatologists disagree on the impact of International Maritime Organization regulations that have capped sulfur content in ship fuel since 2020.
NASA’s Goddard Space Flight Centre has a whiteboard listing 18 research projects related to PACE, including monitoring volcanoes and forest fires and investigating the effects of soot from agricultural fires on marine clouds. The answers to these questions lie in unraveling the behavior of tiny things, and after decades of uncertainty, PACE is poised to provide them.
