[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:08.57,0:00:15.28,Default,,0000,0000,0000,,Cloudy climate change:\NHow clouds affect Earth's temperature.
Dialogue: 0,0:00:15.28,0:00:20.99,Default,,0000,0000,0000,,Earth's average surface temperature\Nhas warmed by .8 Celsius since 1750.
Dialogue: 0,0:00:20.99,0:00:24.58,Default,,0000,0000,0000,,When carbon dioxide concentrations\Nin the atmosphere have doubled,
Dialogue: 0,0:00:24.58,0:00:28.25,Default,,0000,0000,0000,,which is expected before the end\Nof the 21st century,
Dialogue: 0,0:00:28.25,0:00:30.58,Default,,0000,0000,0000,,researchers project global temperatures
Dialogue: 0,0:00:30.58,0:00:35.60,Default,,0000,0000,0000,,will have risen by \N1.5 to 4.5 degrees Celsius.
Dialogue: 0,0:00:35.60,0:00:39.62,Default,,0000,0000,0000,,If the increase is near the low end,\N1.5 Celsius,
Dialogue: 0,0:00:39.62,0:00:43.68,Default,,0000,0000,0000,,then we're already halfway there,\Nand we should be more able to adapt
Dialogue: 0,0:00:43.68,0:00:46.49,Default,,0000,0000,0000,,with some regions becoming drier\Nand less productive,
Dialogue: 0,0:00:46.49,0:00:50.59,Default,,0000,0000,0000,,but others becoming warmer,\Nwetter and more productive.
Dialogue: 0,0:00:50.59,0:00:56.06,Default,,0000,0000,0000,,On the other hand, a rise of 4.5 degrees\NCelsius would be similar in magnitude
Dialogue: 0,0:00:56.06,0:01:01.94,Default,,0000,0000,0000,,to the warming that's occurred since\Nthe last glacial maximum 22,000 years ago,
Dialogue: 0,0:01:01.94,0:01:06.72,Default,,0000,0000,0000,,when most of North America was under\Nan ice sheet two kilometers thick.
Dialogue: 0,0:01:06.72,0:01:11.04,Default,,0000,0000,0000,,So that would represent a \Ndramatic change of climate.
Dialogue: 0,0:01:11.04,0:01:14.75,Default,,0000,0000,0000,,So it's vitally important for scientists\Nto predict the change in temperature
Dialogue: 0,0:01:14.75,0:01:20.29,Default,,0000,0000,0000,,with as much precision as possible\Nso that society can plan for the future.
Dialogue: 0,0:01:20.29,0:01:22.78,Default,,0000,0000,0000,,The present range of uncertainty\Nis simply too large
Dialogue: 0,0:01:22.78,0:01:27.57,Default,,0000,0000,0000,,to be confident of how best\Nto respond to climate change.
Dialogue: 0,0:01:27.57,0:01:33.28,Default,,0000,0000,0000,,But this estimate of 1.5 to 4.5 Celsius\Nfor a doubling of carbon dioxide
Dialogue: 0,0:01:33.28,0:01:36.58,Default,,0000,0000,0000,,hasn't changed in 35 years.
Dialogue: 0,0:01:36.58,0:01:39.71,Default,,0000,0000,0000,,Why haven't we been able \Nto narrow it down?
Dialogue: 0,0:01:39.71,0:01:44.57,Default,,0000,0000,0000,,The answer is that we don't yet understand\Naerosols and clouds well enough.
Dialogue: 0,0:01:44.57,0:01:47.84,Default,,0000,0000,0000,,But a new experiment at CERN\Nis tackling the problem.
Dialogue: 0,0:01:47.84,0:01:50.29,Default,,0000,0000,0000,,In order to predict how\Nthe temperature will change,
Dialogue: 0,0:01:50.29,0:01:53.95,Default,,0000,0000,0000,,scientists need to know something\Ncalled Earth's climate sensitivity,
Dialogue: 0,0:01:53.95,0:01:57.98,Default,,0000,0000,0000,,the temperature change in response\Nto a radiative forcing.
Dialogue: 0,0:01:57.98,0:02:00.64,Default,,0000,0000,0000,,A radiative forcing is \Na temporary imbalance
Dialogue: 0,0:02:00.64,0:02:06.15,Default,,0000,0000,0000,,between the energy received from the Sun\Nand the energy radiated back out to space,
Dialogue: 0,0:02:06.15,0:02:09.64,Default,,0000,0000,0000,,like the imbalance caused by an\Nincrease of greenhouse gases.
Dialogue: 0,0:02:09.64,0:02:13.11,Default,,0000,0000,0000,,To correct the imbalance,\NEarth warms up or cools down.
Dialogue: 0,0:02:13.11,0:02:15.66,Default,,0000,0000,0000,,We can determine Earth's\Nclimate sensitivity
Dialogue: 0,0:02:15.66,0:02:18.03,Default,,0000,0000,0000,,from the experiment that we've already
Dialogue: 0,0:02:18.03,0:02:20.96,Default,,0000,0000,0000,,performed in the industrial age \Nsince 1750
Dialogue: 0,0:02:20.96,0:02:24.52,Default,,0000,0000,0000,,and then use this number to determine\Nhow much more it will warm
Dialogue: 0,0:02:24.52,0:02:29.19,Default,,0000,0000,0000,,for various projected radiative forcings\Nin the 21st century.
Dialogue: 0,0:02:29.19,0:02:31.59,Default,,0000,0000,0000,,To do this, we need to know\Ntwo things:
Dialogue: 0,0:02:31.59,0:02:35.56,Default,,0000,0000,0000,,First, the global temperature rise\Nsince 1750,
Dialogue: 0,0:02:35.56,0:02:39.35,Default,,0000,0000,0000,,and second, the radiative forcing\Nof the present day climate
Dialogue: 0,0:02:39.35,0:02:42.48,Default,,0000,0000,0000,,relative to the pre-industrial climate.
Dialogue: 0,0:02:42.48,0:02:45.04,Default,,0000,0000,0000,,For the radiative forcings,\Nwe know that human activities
Dialogue: 0,0:02:45.04,0:02:47.56,Default,,0000,0000,0000,,have increased greenhouse gases\Nin the atmosphere,
Dialogue: 0,0:02:47.56,0:02:49.65,Default,,0000,0000,0000,,which have warmed the planet.
Dialogue: 0,0:02:49.65,0:02:53.35,Default,,0000,0000,0000,,But our activities have at the same time\Nincreased the amount
Dialogue: 0,0:02:53.35,0:02:57.79,Default,,0000,0000,0000,,of aerosol particles in clouds,\Nwhich have cooled the planet.
Dialogue: 0,0:02:57.79,0:03:01.13,Default,,0000,0000,0000,,Pre-industrial greenhouse gas\Nconcentrations are well measured
Dialogue: 0,0:03:01.13,0:03:05.44,Default,,0000,0000,0000,,from bubbles trapped in ice cores\Nobtained in Greenland and Antarctica.
Dialogue: 0,0:03:05.44,0:03:08.90,Default,,0000,0000,0000,,So the greenhouse gas forcings\Nare precisely known.
Dialogue: 0,0:03:08.90,0:03:14.24,Default,,0000,0000,0000,,But we have no way of directly measuring\Nhow cloudy it was in 1750.
Dialogue: 0,0:03:14.24,0:03:19.22,Default,,0000,0000,0000,,And that's the main source of uncertainty\Nin Earth's climate sensitivity.
Dialogue: 0,0:03:19.22,0:03:21.60,Default,,0000,0000,0000,,To understand pre-industrial cloudiness,
Dialogue: 0,0:03:21.60,0:03:24.40,Default,,0000,0000,0000,,we must use computer models\Nthat reliably simulate
Dialogue: 0,0:03:24.40,0:03:28.40,Default,,0000,0000,0000,,the processes responsible for \Nforming aerosols in clouds.
Dialogue: 0,0:03:28.40,0:03:32.04,Default,,0000,0000,0000,,Now to most people, aerosols are the thing\Nthat make your hair stick,
Dialogue: 0,0:03:32.04,0:03:34.26,Default,,0000,0000,0000,,but that's only one type of aerosol.
Dialogue: 0,0:03:34.26,0:03:39.12,Default,,0000,0000,0000,,Atmospheric aerosols are tiny liquid\Nor solid particles suspended in the air.
Dialogue: 0,0:03:39.12,0:03:40.57,Default,,0000,0000,0000,,They are either primary,
Dialogue: 0,0:03:40.57,0:03:44.39,Default,,0000,0000,0000,,from dust, sea spray salt\Nor burning biomass,
Dialogue: 0,0:03:44.39,0:03:49.19,Default,,0000,0000,0000,,or secondary, formed by gas to\Nparticle conversion in the atmosphere,
Dialogue: 0,0:03:49.19,0:03:51.94,Default,,0000,0000,0000,,also known as particle nucleation.
Dialogue: 0,0:03:51.94,0:03:54.79,Default,,0000,0000,0000,,Aerosols are everywhere in the atmosphere,
Dialogue: 0,0:03:54.79,0:03:58.28,Default,,0000,0000,0000,,and they can block out the sun\Nin polluted urban environments,
Dialogue: 0,0:03:58.28,0:04:01.75,Default,,0000,0000,0000,,or bathe distant mountains in a blue haze.
Dialogue: 0,0:04:01.75,0:04:07.56,Default,,0000,0000,0000,,More importantly, a cloud droplet cannot\Nform without an aerosol particle seed.
Dialogue: 0,0:04:07.56,0:04:11.32,Default,,0000,0000,0000,,So without aerosol particles,\Nthere'd be no clouds,
Dialogue: 0,0:04:11.32,0:04:14.20,Default,,0000,0000,0000,,and without clouds,\Nthere'd be no fresh water.
Dialogue: 0,0:04:14.20,0:04:18.51,Default,,0000,0000,0000,,The climate would be much hotter,\Nand there would be no life.
Dialogue: 0,0:04:18.51,0:04:22.64,Default,,0000,0000,0000,,So we owe our existence\Nto aerosol particles.
Dialogue: 0,0:04:22.64,0:04:24.21,Default,,0000,0000,0000,,However, despite their importance,
Dialogue: 0,0:04:24.21,0:04:26.74,Default,,0000,0000,0000,,how aerosol particles form\Nin the atmosphere
Dialogue: 0,0:04:26.74,0:04:30.33,Default,,0000,0000,0000,,and their effect on clouds \Nare poorly understood.
Dialogue: 0,0:04:30.33,0:04:33.68,Default,,0000,0000,0000,,Even the vapors responsible\Nfor aerosol particle formation
Dialogue: 0,0:04:33.68,0:04:35.28,Default,,0000,0000,0000,,are not well established
Dialogue: 0,0:04:35.28,0:04:38.20,Default,,0000,0000,0000,,because they're present in only\Nminute amounts,
Dialogue: 0,0:04:38.20,0:04:42.41,Default,,0000,0000,0000,,near one molecule per million million\Nmolecules of air.
Dialogue: 0,0:04:42.41,0:04:45.30,Default,,0000,0000,0000,,This lack of understanding\Nis the main reason
Dialogue: 0,0:04:45.30,0:04:48.29,Default,,0000,0000,0000,,for the large uncertainty \Nin climate sensitivity,
Dialogue: 0,0:04:48.29,0:04:52.68,Default,,0000,0000,0000,,and the corresponding wide range\Nof future climate projections.
Dialogue: 0,0:04:52.68,0:04:58.54,Default,,0000,0000,0000,,However, an experiment underway at CERN,\Nnamed, perhaps unsurprisingly, "Cloud"
Dialogue: 0,0:04:58.54,0:05:01.30,Default,,0000,0000,0000,,has managed to build a steel vessel\Nthat's large enough
Dialogue: 0,0:05:01.30,0:05:05.100,Default,,0000,0000,0000,,and has a low enough contamination,\Nthat aerosol formation can,
Dialogue: 0,0:05:05.100,0:05:11.23,Default,,0000,0000,0000,,for the first time, be measured under\Ntightly controlled atmospheric conditions
Dialogue: 0,0:05:11.23,0:05:13.09,Default,,0000,0000,0000,,in the laboratory.
Dialogue: 0,0:05:13.09,0:05:17.18,Default,,0000,0000,0000,,In its first five years of operation,\NCloud has identified the vapors
Dialogue: 0,0:05:17.18,0:05:20.61,Default,,0000,0000,0000,,responsible for aerosol particle\Nformation in the atmosphere,
Dialogue: 0,0:05:20.61,0:05:24.42,Default,,0000,0000,0000,,which include sulfuric acid,\Nammonia, amines,
Dialogue: 0,0:05:24.42,0:05:27.06,Default,,0000,0000,0000,,and biogenic vapors from trees.
Dialogue: 0,0:05:27.06,0:05:30.60,Default,,0000,0000,0000,,Using an ionizing particle beam\Nfrom the CERN proton synchrotron,
Dialogue: 0,0:05:30.60,0:05:34.84,Default,,0000,0000,0000,,Cloud is also investigating\Nif galactic cosmic rays
Dialogue: 0,0:05:34.84,0:05:38.86,Default,,0000,0000,0000,,enhance the formation of \Naerosols in clouds.
Dialogue: 0,0:05:38.86,0:05:43.53,Default,,0000,0000,0000,,This has been suggested as a possible\Nunaccounted natural climate forcing agent
Dialogue: 0,0:05:43.53,0:05:47.08,Default,,0000,0000,0000,,since the flux of cosmic rays raining\Ndown on the atmosphere
Dialogue: 0,0:05:47.08,0:05:49.92,Default,,0000,0000,0000,,varies with solar activity.
Dialogue: 0,0:05:49.92,0:05:53.46,Default,,0000,0000,0000,,So Cloud is addressing two big questions:
Dialogue: 0,0:05:53.46,0:05:57.60,Default,,0000,0000,0000,,Firstly, how cloudy was the \Npre-industrial climate?
Dialogue: 0,0:05:57.60,0:06:03.07,Default,,0000,0000,0000,,And, hence, how much have\Nclouds changed due to human activities?
Dialogue: 0,0:06:03.07,0:06:08.23,Default,,0000,0000,0000,,That knowledge will help sharpen\Nclimate projections in the 21st century.
Dialogue: 0,0:06:08.23,0:06:12.74,Default,,0000,0000,0000,,And secondly, could the puzzling\Nobservations of solar climate variability
Dialogue: 0,0:06:12.74,0:06:15.94,Default,,0000,0000,0000,,in the pre-industrial climate be explained\Nby an influence
Dialogue: 0,0:06:15.94,0:06:18.53,Default,,0000,0000,0000,,of galactic cosmic rays on clouds?
Dialogue: 0,0:06:18.53,0:06:23.74,Default,,0000,0000,0000,,Ambitious but realistic goals\Nwhen your head's in the clouds.