emergency medicine for climate TO REDUCE WARMING rapidly and temporarily

The world currently lacks options to significantly reduce warming before 2050, or within a few years if needed, to keep people safe and prevent accelerating climate changes. Climate interventions are proposed approaches to accelerating the removal of greenhouse gases or reducing the amount of heat energy in the climate system in order to reduce warming and its impacts.

Scientific assessments have found that one of the most promising approaches to reducing warming within a few years (once developed) is increasing the reflection of sunlight from clouds and particles in the atmosphere, “sunlight reflection modification” (SRM) or “solar climate intervention” (SCI), sometimes called “solar geoengineering”. Based on one of the ways nature cools the planet, It is estimated that increasing the reflection of sunlight from Earth’s atmosphere by just 1% might reduce warming substantially, keeping people safe and natural systems stable while greenhouse gases are reduced.

This atmospheric sunlight reflection effect has been observed when large volcanos release material into the stratosphere, cooling climate, and when pollution particles mix with clouds and increase their brightness, which is understood to be offsetting some greenhouse gas warming today. One of the most sophisticated climate modeling studies to date of and intentional sunlight reflection intervention simulated Earth’s climate in a scenario with high emissions against a scenario in which particles are dispersed in the stratosphere to increase sunlight reflection from 2024-2100.  In the scenario with this type of climate intervention, nearly all parts of the world had surface temperatures approximating today’s and were safer for people than those in the simulations without intervention.

There are, however, considerable risks to these approaches, including changes in precipitation, atmospheric circulation and clouds, that must be better understood to determine whether interventions could be included seriously considered as part of the portfolio of climate responses. These risks must be assessed and weighed against the escalating risks of warming.

the most promising Approaches ARE Based on Observations from Nature

Scientific assessments have recommended for research several proposed approaches for increasing the reflection of sunlight from the atmosphere, operating at different layers, from the lowest (the boundary layer) to one of the highest (the stratosphere).

Marine Cloud Brightening

Today, particles from pollution and their brightening effect on clouds in the lower atmosphere are thought to be producing a significant cooling effect that offsets some warming. The IPCC estimates this “cloud-aerosol” cooling effect to be somewhere between 0.5 and 1.1°C.  Specifically, emissions from ships have a marked effect on the brightness of ocean clouds, that can be seen in observations from space as “ship-tracks.” One proposed approach to cooling climate is to spray salt mist from sea water, from ships or autonomous vessels, into regions of susceptible marine stratocumulus clouds in a way that optimizes the cloud-aerosol effect. Studies suggest that by brightening 10-25% of these clouds (representing 3-5% of the ocean’s surface), it may be possible to offset a doubling of CO2. But the magnitude of the effect is uncertain without more research, and effects on weather and circulation are an area of concern.

Stratospheric Sunlight Reflection

In 1991, emissions from the eruption of Mount Pinatubo cooled the planet by 0.5 °C for nearly two years, leading to a recovery of Arctic ice during the period. Scientists have proposed that there may be more optimized ways to disperse particles in the stratosphere—possibly with cleaner materials—to produce a similar cooling effect. Historical observations provide a high degree of confidence in the cooling that can be produced in this way, and uncertainties center on the risks, particularly as they might unfold over time periods longer than the lifespan of particles in the stratosphere (a year or two). In particular, scientists hope to explore the effect on the chemistry of the stratosphere that might lead to damage to the ozone layer or changes in atmospheric circulation. Related to this, researchers hope to study both the effects of material released by volcanoes (SO2) and other materials that may have more favorable properties (calcium carbonate or diamonds).

Cirrus Cloud Thinning

Cirrus clouds in the upper troposphere reflect more sunlight back to Earth than they reflect out to space, so by 'thinning' the reflective capacity of these clouds more light could be released from below into space. This could be done by injecting particles into cirrus clouds that catalyze the formation of ice crystals in the clouds, causing them to precipitate and 'thin.' A form of tis effect is thought to happen today, in reverse, as aircraft fly through cirrus clouds releasing emissions that have been observed to cause the clouds to grow slightly “thicker” trapping heat and increasing climate warming.  

Imperative for research

There are a number of emerging research efforts to determine the feasibility and risks of climate interventions to help slow Earth's warming. But research is very nascent, and scientists think it could take a decade of research to evaluate these approaches, including both specific research in interventions and accelerating observations and predictions of the Earth system. This work is imperative so that policymakers and members of society are equipped to assess the risk and benefits of these approaches against escalating near-term climate risks and the need to ensure safety. 

SUNLIGHT REFLECTION BRIEFING

In June 2020, SilverLining held a briefing on the state of play in research on increasing the reflection of sunlight from the atmosphere to cool climate. The event featured leading efforts in the U.S. and other parts of the world, including remarks from scientific leaders at the Intergovernmental Panel on Climate Change (IPCC), National Oceanic and Atmospheric Administration (NOAA) and National Center for Atmospheric Research (NCAR). David Biello, science curator for TED, moderated the event, and philanthropic funders Chris Sacca and Rachel Pritzker shared perspectives.