Placeholder Image

字幕表 動画を再生する

  • I'm here to talk to you about something important that may be new to you.

  • The governments of the world

  • are about to conduct an unintentional experiment

  • on our climate.

  • In 2020, new rules will require ships to lower their sulfur emissions

  • by scrubbing their dirty exhaust

  • or switching to cleaner fuels.

  • For human health, this is really good,

  • but sulfur particles in the emission of ships

  • also have an effect on clouds.

  • This is a satellite image of marine clouds

  • off the Pacific West Coast of the United States.

  • The streaks in the clouds are created by the exhaust from ships.

  • Ships' emissions include both greenhouse gases,

  • which trap heat over long periods of time,

  • and particulates like sulfates that mix with clouds

  • and temporarily make them brighter.

  • Brighter clouds reflect more sunlight back to space,

  • cooling the climate.

  • So in fact,

  • humans are currently running two unintentional experiments

  • on our climate.

  • In the first one, we're increasing the concentration of greenhouse gases

  • and gradually warming the earth system.

  • This works something like a fever in the human body.

  • If the fever remains low, its effects are mild,

  • but as the fever rises, damage grows more severe

  • and eventually devastating.

  • We're seeing a little of this now.

  • In our other experiment,

  • we're planning to remove a layer of particles

  • that brighten clouds and shield us from some of this warming.

  • The effect is strongest in ocean clouds like these,

  • and scientists expect the reduction of sulfur emissions from ships next year

  • to produce a measurable increase in global warming.

  • Bit of a shocker?

  • In fact, most emissions contain sulfates that brighten clouds:

  • coal, diesel exhaust, forest fires.

  • Scientists estimate that the total cooling effect from emission particles,

  • which they call aerosols when they're in the climate,

  • may be as much as all of the warming we've experienced up until now.

  • There's a lot of uncertainty around this effect,

  • and it's one of the major reasons why we have difficulty predicting climate,

  • but this is cooling that we'll lose as emissions fall.

  • So to be clear, humans are currently cooling the planet

  • by dispersing particles into the atmosphere at massive scale.

  • We just don't know how much, and we're doing it accidentally.

  • That's worrying,

  • but it could mean that we have a fast-acting way to reduce warming,

  • emergency medicine for our climate fever if we needed it,

  • and it's a medicine with origins in nature.

  • This is a NASA simulation of earth's atmosphere,

  • showing clouds and particles moving over the planet.

  • The brightness is the Sun's light reflecting from particles in clouds,

  • and this reflective shield is one of the primary ways

  • that nature keeps the planet cool enough for humans

  • and all of the life that we know.

  • In 2015, scientists assessed possibilities for rapidly cooling climate.

  • They discounted things like mirrors in space,

  • ping-pong balls in the ocean, plastic sheets on the Arctic,

  • and they found that the most viable approaches

  • involved slightly increasing this atmospheric reflectivity.

  • In fact, it's possible that reflecting just one or two percent more sunlight

  • from the atmosphere

  • could offset two degrees Celsius or more of warming.

  • Now, I'm a technology executive, not a scientist.

  • About a decade ago, concerned about climate,

  • I started to talk with scientists about potential countermeasures to warming.

  • These conversations grew into collaborations

  • that became the Marine Cloud Brightening Project,

  • which I'll talk about momentarily,

  • and the nonprofit policy organization SilverLining, where I am today.

  • I work with politicians, researchers,

  • members of the tech industry and others

  • to talk about some of these ideas.

  • Early on, I met British atmospheric scientist John Latham,

  • who proposed cooling the climate the way that the ships do,

  • but with a natural source of particles:

  • sea-salt mist from seawater

  • sprayed from ships into areas of susceptible clouds over the ocean.

  • The approach became known by the name I gave it then,

  • "marine cloud brightening."

  • Early modeling studies suggested that by deploying marine cloud brightening

  • in just 10 to 20 percent of susceptible ocean clouds,

  • it might be possible to offset as much as two degrees Celsius's warming.

  • It might even be possible to brighten clouds in local regions

  • to reduce the impacts caused by warming ocean surface temperatures.

  • For example, regions such as the Gulf Atlantic

  • might be cooled in the months before a hurricane season

  • to reduce the force of storms.

  • Or, it might be possible to cool waters flowing onto coral reefs

  • overwhelmed by heat stress,

  • like Australia's Great Barrier Reef.

  • But these ideas are only theoretical,

  • and brightening marine clouds is not the only way

  • to increase the reflection of the sunlight from the atmosphere.

  • Another occurs when large volcanoes release material with enough force

  • to reach the upper layer of the atmosphere, the stratosphere.

  • When Mount Pinatubo erupted in 1991,

  • it released material into the stratosphere,

  • including sulfates that mix with the atmosphere to reflect sunlight.

  • This material remained and circulated around the planet.

  • It was enough to cool the climate by over half a degree Celsius

  • for about two years.

  • This cooling led to a striking increase in Arctic ice cover in 1992,

  • which dropped in subsequent years as the particles fell back to earth.

  • But the volcanic phenomenon led Nobel Prize winner Paul Crutzen

  • to propose the idea that dispersing particles into the stratosphere

  • in a controlled way might be a way to counter global warming.

  • Now, this has risks that we don't understand,

  • including things like heating up the stratosphere

  • or damage to the ozone layer.

  • Scientists think that there could be safe approaches to this,

  • but is this really where we are?

  • Is this really worth considering?

  • This is a simulation

  • from the US National Center for Atmospheric Research

  • global climate model showing, earth surface temperatures through 2100.

  • The globe on the left visualizes our current trajectory,

  • and on the right, a world where particles are introduced into the stratosphere

  • gradually in 2020,

  • and maintained through 2100.

  • Intervention keeps surface temperatures near those of today,

  • while without it, temperatures rise well over three degrees.

  • This could be the difference between a safe and an unsafe world.

  • So, if there's even a chance that this could be close to reality,

  • is this something we should consider seriously?

  • Today, there are no capabilities,

  • and scientific knowledge is extremely limited.

  • We don't know whether these types of interventions are even feasible,

  • or how to characterize their risks.

  • Researchers hope to explore some basic questions

  • that might help us know whether or not these might be real options

  • or whether we should rule them out.

  • It requires multiple ways of studying the climate system,

  • including computer models to forecast changes,

  • analytic techniques like machine learning,

  • and many types of observations.

  • And though it's controversial,

  • it's also critical that researchers develop core technologies

  • and perform small-scale, real-world experiments.

  • There are two research programs proposing experiments like this.

  • At Harvard, the SCoPEx experiment would release very small amounts

  • of sulfates, calcium carbonate and water into the stratosphere with a balloon,

  • to study chemistry and physics effects.

  • How much material?

  • Less than the amount released in one minute of flight

  • from a commercial aircraft.

  • So this is definitely not dangerous,

  • and it may not even be scary.

  • At the University of Washington,

  • scientists hope to spray a fine mist of salt water into clouds

  • in a series of land and ocean tests.

  • If those are successful, this would culminate in experiments

  • to measurably brighten an area of clouds over the ocean.

  • The marine cloud brightening effort is the first to develop any technology

  • for generating aerosols for atmospheric sunlight reflection in this way.

  • It requires producing very tiny particles --

  • think about the mist that comes out of an asthma inhaler --

  • at massive scale -- so think of looking up at a cloud.

  • It's a tricky engineering problem.

  • So this one nozzle they developed

  • generates three trillion particles per second,

  • 80 nanometers in size,

  • from very corrosive saltwater.

  • It was developed by a team of retired engineers in Silicon Valley --

  • here they are --

  • working full-time for six years, without pay, for their grandchildren.

  • It will take a few million dollars and another year or two

  • to develop the full spray system they need to do these experiments.

  • In other parts of the world, research efforts are emerging,

  • including small modeling programs at Beijing Normal University in China,

  • the Indian Institute of Science,

  • a proposed center for climate repair at Cambridge University in the UK

  • and the DECIMALS Fund,

  • which sponsors researchers in global South countries

  • to study the potential impacts of these sunlight interventions

  • in their part of the world.

  • But all of these programs, including the experimental ones,

  • lack significant funding.

  • And understanding these interventions is a hard problem.

  • The earth is a vast, complex system

  • and we need major investments in climate models, observations

  • and basic science

  • to be able to predict climate much better than we can today

  • and manage both our accidental and any intentional interventions.

  • And it could be urgent.

  • Recent scientific reports predict that in the next few decades,

  • earth's fever is on a path to devastation:

  • extreme heat and fires,

  • major loss of ocean life,

  • collapse of Arctic ice,

  • displacement and suffering for hundreds of millions of people.

  • The fever could even reach tipping points where warming takes over

  • and human efforts are no longer enough

  • to counter accelerating changes in natural systems.

  • To prevent this circumstance,

  • the UN's International Panel on Climate Change predicts

  • that we need to stop and even reverse emissions by 2050.

  • How? We have to quickly and radically transform major economic sectors,

  • including energy, construction, agriculture, transportation and others.

  • And it is imperative that we do this as fast as we can.

  • But our fever is now so high

  • that climate experts say we also have to remove

  • massive quantities of CO2 from the atmosphere,

  • possibly 10 times all of the world's annual emissions,

  • in ways that aren't proven yet.

  • Right now, we have slow-moving solutions to a fast-moving problem.

  • Even with the most optimistic assumptions,

  • our exposure to risk in the next 10 to 30 years

  • is unacceptably high, in my opinion.

  • Could interventions like these provide fast-acting medicine if we need it

  • to reduce the earth's fever while we address its underlying causes?

  • There are real concerns about this idea.

  • Some people are very worried that even researching these interventions

  • could provide an excuse to delay efforts to reduce emissions.

  • This is also known as a moral hazard.

  • But, like most medicines,

  • interventions are more dangerous the more that you do,

  • so research actually tends to draw out the fact

  • that we absolutely, positively cannot continue

  • to fill up the atmosphere with greenhouse gases,

  • that these kinds of alternatives are risky

  • and if we were to use them,

  • we would need to use as little as possible.

  • But even so,

  • could we ever learn enough about these interventions

  • to manage the risk?

  • Who would make decisions about when and how to intervene?

  • What if some people are worse off,

  • or they just think they are?

  • These are really hard problems.

  • But what really worries me is that as climate impacts worsen,

  • leaders will be called on to respond by any means available.

  • I for one don't want them to act without real information

  • and much better options.

  • Scientists think it will take a decade of research

  • just to assess these interventions,

  • before we ever were to develop or use them.

  • Yet today, the global level of investment in these interventions

  • is effectively zero.

  • So, we need to move quickly

  • if we want policymakers to have real information

  • on this kind of