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May 31, 2006

An Inconvenient Truth: Review

My friend Ryan's dad is a famous polar zoologist. Several years ago, I asked Ryan what his dad thought about "the whole global warming thing."

"Well, my dad's an optimist about global warming," Ryan said.

I breathed an inward sigh of relief.

"He's not nearly as dark as a lot of his colleagues."

I began to hope that the crisis had been exaggerated.

"My dad just thinks that global warming is going to kill off all the indigenous peoples and most of the wildlife in the arctic."

Last night I went to see Al Gore's new anti-global warming movie, An Inconvenient Truth (IMDB). I was very impressed. It's not great art, but it's terrific science. More importantly, it's an easily accessible message that everyone needs to hear. Go see it whether you feel like it or not and take your kids.

Al Gore lays out the evidence of an impending climate crisis clearly, rigorously, and compellingly. Given the profound implications Gore's argument, it seems almost perverse to dwell on the movie's aesthetics or its implications for American presidential politics. An Inconvenient Truth deserves to be assessed as a scientific, political, and moral argument for American leadership in the fight against global warming.

An Inconvenient Truth is the film version of Al Gore's famous global warming lecture, a free multi-media presentation he has delivered to thousands of people in dozens of cities around the world. Lecture footage and graphics are interspersed with biographical vignettes about Gore and staged footage of life on the anti-global warming sawdust trail.

Gore explains global warming terms that anyone can understand: Burning releases carbon, and carbon gets trapped in the atmosphere. Sunlight comes through the atmosphere and warms the earth, but carbon traps the heat, so temperatures rise. This phenomenon has been described as the greenhouse effect because carbon acts like the glass in a greenhouse. Sunlight goes in and turns to heat, but the heat can't escape because the glass insulates the greenhouse.

The caged heat is warming up the oceans. Icebergs shrink, glaciers retreat, and polar ice melts. Currently, giant ice masses like Greenland serve as giant mirrors that deflect sunlight back into space. However, as the surrounding water heats up, that ice begins to melt. More melting means less surface area for deflection. Less deflection means more heat absorption by the surrounding water, which in turn accelerates melting.

I didn't know this until the day before I saw the movie, but Ryan's dad gave Gore some of his slides on the melting ice in Greenland. Our fellow movie-goers probably thought it was a little weird when we started applauding for Dr. McCarthy's credit.

One of the best scenes in the movie is when Gore describes his trip under the North Pole on a nuclear sub. Submarine crews have been meticulously monitoring the thickness of the ice for decades because subs can only surface through relatively thin ice. Previously, these measurements were classified. Gore explains how he went up north to convince authorities to release this important data. The submariners' graph is now part of Gore's slide deck. It's just one of the innumerable pieces of converging evidence that the earth is warming up all over, especially at the poles.

A large percentage of the world's fresh water is locked away in ice. Millions of people get their drinking water from the runoff of glaciers, but glaciers are shrinking all over the world. Gore shows a long series of dramatic "before" and "after" shots of shrinking glaciers from Mount Kilimanjaro, to Patagonia, to Glacier National Park. (Links for illustration, not shots from the film.) If glacial melting continues, millions of people could face water shortages.

Furthermore, warming causes both floods and droughts. Hotter weather increases evaporation from the soil, exacerbating droughts and dustbowls. Rising temperatures also give rise to more violent storms by increasing evaporation from the seas. Storms also get stronger when they travel over warmer water. See RealClimate for a sober look at Katrina, global warming, and loaded dice.

Even more seriously, rising temperatures threaten ice reserves in the arctic and the antarctic. One of the most alarming signs of global warming the unprecedented ice breakup on the Antarctic Peninsula:

Antarctic Peninsula - Collapsing ice-shelf, January-February 2002. The northern section of the Larsen B ice shelf, an area of 1,250 square miles (3,250 km2), disintegrated in a period of 35 days. This was the largest collapse event of the last 30 years, bringing the total loss of ice extent from seven ice shelves to 6,760 square miles (17,500 km2) since 1974. The ice retreat is attributed to the regions strong warming trend - 4.5F (2.5C) in the last 50 years. [Climate Hot Map]

Gore explains that Antarctica has both land-based ice and sea-based ice. The floating ice is melting much faster than scientists expected it to. The rapid depletion of sea-based ice is exposing land-based ice to warmer temperatures. So, land-based ice is now melting much faster than expected.

The recent surge in land-based ice melting is alarming because of the implications for global sea levels. Land-based ice is ice propped up above sea level. If it melts, the runoff increases sea levels. (An floating iceberg that melts in the sea won't raise sea levels for the same reason that an ice cube floating in a drink won't overflow the glass when it melts.)

If a big chunk of land ice were to melt, world sea levels could rise by up to 20 feet. Gore shows a simulation of what a 20-foot rise in sea level would do to coastal cities around the world. One animation superimposed the effects of this 20-foot jump on a map of Manhattan, including the WTC memorial. It was eerie to sit in a Lower East Side theater straining to pick out the building I was sitting in on the satellite image before it disappeared under the advancing blue front.

One thing Gore doesn't explain clearly enough is how long it would take for world sea levels to rise by 20 feet if a major melting crisis happened. A year? Two years? A few months? The animation doesn't specify the timeframe. The take home message is not that people will drown en-masse as they did in New Orleans, but rather a large percentage of the world's coastal cities would have to be abandoned.

Melting ice also dilutes the sea. Salinity is integral to the ocean current systems regulate the global climate. The gulfstream is part of a so-called conveyer belt that carriers warm water from the Southern hemisphere northwards. The warm surface currents modulate the climates of the land masses they pass. These warm currents provide Europe with one third as much warmth as direct sunlight. Surface currents also become saltier as they travel because of evaporation. Eventually, this water gets cold enough and salty enough to sink to the bottom and resume the cycle.

If Greenland were to melt rapidly, massive amounts of fresh water could be released into the sea. If the salt levels dropped too much, the conveyer belt could stop working because the warmer water wouldn't sink back down again. Geologists say that the last time this system broke down, Europe was enveloped by an ice age in as little as a decade.

Real Climate's review of An Inconvenient Truth gives the production high marks for scientific accuracy. However, the review's author notes that projecting future temperatures based on the past correlations between carbon dioxide and the projected carbon levels may overestimate the expected rise in temperature. The reviewer doesn't doubt that temperatures will rise because of CO2, he just thinks that they may not rise quite as much you might think based on past correlations between CO2 and temperature because other cooling trends may offset the effects of CO2. If I remember correctly, Gore doesn't actually project the temperature forward. He superimposes the graphs of global temperature and global carbon levels. The carbon line gets projected into the future, but the temperature line stops at the present. Gore invites the viewer to look at the block-long pattern of correlations and infer what the temperature will do as carbon emissions rise exponentially.

The central plank of global warming denial is that that correlation isn't causation. Even skeptics can't deny the basic greenhouse mechanism. Nor can they deny that global temperature has been closely correlated with carbon dioxide levels for tens of thousands of years. There's no getting around the fact that human beings are adding vastly more carbon to the earth's atmosphere than it has ever contained. The two major culprits are fossil fuels and burning tropical forests. Increasing industrialization and population growth can be expected to accelerate carbon emission trends. Tellingly, the earth's temperature has been rising more or less proportionately to the increases in atmospheric carbon since the industrial revolution.

Still, we can't do controlled experiments with the world's climate. Any evidence that increased carbon levels cause increased temperatures in the real world is going to be correlational. Any evidence about the likely mechanisms of global warming that is based on models or laboratory experiments can be dismissed as being unrealistically simplistic. (Of course, the hired shills will also dismiss as mere correlation the fact that their denials are highly correlated with their pay checks from the oil and gas lobby.) This self-sealing rhetoric of denial more or less guarantees that we will be submerged without knowing that global warming is real.

We can only hope that movies like An Inconvenient Truth can cut through the haze of disinformation and denial.


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» Optimism from Political Animal
OPTIMISM....Lindsay Beyerstein passes along the following anecdote about what the word optimist means when the subject is global warming:My friend Ryan's dad is a famous polar zoologist. Several years ago, I asked Ryan what his dad thought about "the w... [Read More]

» Optimism from Political Animal
OPTIMISM....Lindsay Beyerstein passes along the following anecdote about what the word optimist means when the subject is global warming:My friend Ryan's dad is a famous polar zoologist. Several years ago, I asked Ryan what his dad thought about "the w... [Read More]

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Every now and then the world is trying to tell you something, and events conspire in a flash of synchronicity to reveal a truth so deep and powerful that ordinary genius alone would have been insufficient to figure it out. Such was the case recently,... [Read More]


Yes! Go See it. You may think you won't hear a word of news in this movie. You may, like me, have spent the last decade nagging anyone who wouldn't run away that they should consider this a serious problem and change their personal ways and voting habits. Go see it anyway. You're needed as witnesses to see what the rest of the audiance is picking up, if anything. You are going to be educated by seeing who comes and how full the the theater is. And the box office reciepts are standing in for polling numbers these days. Don't wait for the goddamned tipping point, go tip something!

Lindsay B., having spent the last 20 years of my life following this issue fairly closely, would "An Inconvenient Truth" be worth watching for the presentation alone?

David, I wouldn't say that it's worth watching for pure aesthetic value (at least, not in the sense of being a stellar example of the art of documentary filmmaking).

However, if you're interested in the subject matter, I predict that you'll enjoy it. There's a lot of good still footage that I hadn't seen: retreating glaciers, fracturing ice shelfs, trucks on the highway to ANWR sinking into the road because the permafrost melted, a nuclear sub surfacing through the polar ice, etc. The satellite simulation of rising sea levels is really cool because the picture is so clear that almost anyone who lives in Lower Manhattan or Brooklyn could probably pick out their home.

Good thorough review. (Personally, I thought that the look at Gore's life, which the director smoothly wrapped around the science, also helped a lot.)

The reason Gore doesn't "explain" how fast the oceans will rise is that we still don't know. Currently the rise in the ocean is progressing at less than an inch a year, and is not a great threat to U.S. cities. But scientists fear that "feedback loops" (such as the disappearing ice at the North Pole, which Gore explains very well) could accelerate the melting of the ice enormously; already ice in Greenland is melting at 250% of what scientists expected just five years ago.

It's worth discussing this point, I think, because it's an example of how thoughtfully Gore discusses the risks of our current uncontrolled experiment with our climate, without recklessly prophesizing disaster.

Kit makes a good point about how we don't know if a "feedback loop" would accelerate global-level changes in climate. The denialists always love to portray climate models as having "extreme" results, but the fact is that they are fairly conservative. Doubt on what will happen to the Earth's climate does cut both ways, in other words. Gore, if anything, is being cautious in his own conclusions.

the 2nd to last link is broken: "These warm currents provide Europe with one third as much warmth as the sun."

An iceberg floating in the sea won't raise sea levels for the same reason that an ice cube floating in a drink won't overflow the glass when it melts.

I assume you meant "an iceberg floating in the sea won't raise sea levels when it melts for the same reason...." Icebergs themselves, of course, raise sea level just fine.

Thanks, Mark, and epitaph. I'll fix those.

It's not the melting but the warming that causes the rise in sea level. Heating a liquid causes it to expand.

David - go see it. If you're anywhere near as eager to chat with nonspecialists and inform them about what you do, it's worth seeing things that might trigger questions you are well placed to answer. Seeing the movie will better arm you to give relevant and enlightening answers. I'm a big believer in education by chatting with people.

I understand that we're entering a period of increased solar activity : I won't insult you by spelling out what this means to time-lines.

Excellent review! Thanks for the well written synopsis, I will defiantly check out this film. Also, was wondering if the thawing of permafrost was addressed. It has been stated that as the permafrost thaws and oxidizes, it releases yet another green house gas: methane. Again, compounding the current situation.

Don’t just take Gore’s word for it, check out the glaciers:

Long-Term Change Photograph Pairs (Glaciers)

USGS repeat photography project
Glacier National Park, MT

Animations Glacier Bay N.P

Glacier Peak N. Cascade, WA

Nice on-line glacilology lesson-

to David Wilford:

I also have followed climate change for the past twenty years. It is worth it to you to see the movie so you can assess the science, and so you will have seen the basics on which people who question you will base their queries. It is good to see just to see the quality of the lay science that is presented, as well as the quality of the presentation. I was pleased to see a documentary that does not talk down to its audience, and expects them to be able to understand basic science and relational graphs.

The June 6 National Review has an article, " Scare of the Century " that presents an alternate view. Jason Lee Steorts claims that " the alarms and assertions about global warming have gone too far "

Among other points: " The world has two major ice sheets, one covering Greenland, and the other covering most of Antarctica. While melting sea ice has captured its share of attention, its the land sheets that matter ... [ as respects concern to rising sea levels ]...Sea ice is already in the water so its melting does not raise ocean levels."

University of Virginia climate scientist Patrick J. Michaels says that Anctarctica has been gaining ice..because of higher than previously recorded snowfall levels.

A study published in Science in 2005 found that Antarctica gained 45 billion tons of ice per year between 1992 and 2003.

There are other facts and studies mentioned here that are not mentioned in the movie. I don't think that it aims to say global warming is bullshit, only that it's a vastly more complex issue than Gore and others make it out to be.

I recomemend this article, which unfortunately isn't available online to nonsubscribers.

I'm sure it's a total coincidence, but in the Atlantic basin, using barometric pressure as the metric, 3 of the 6 most powerful storms on record (Wilma, Rita, Katrina) occurred in 2005. The other three storms in the top six are Gilbert, Labor Day, and Allen.

My father and I (who both grew up in Florida and Texas) watched in amazement as Katrina, then Rita, and then Wilma, zoomed up to category 5, each faster than the NHC/NOAA was predicting. We both wonder if perhaps the water somewhat below the surface (that gets churned up by hurricane winds) is also warming up and removing some of the self-limit on hurricane strength.

Your comment on water temperature is probably accurate...but hurricane cycles are believed to be hundreds of years long, so there may be no connection between hurricane cycles and human activity.

From National Geographic article linked:
Landsen and Gray, the Colorado State University meteorologist, think the increased number of hurricanes is part of a weather cycle that's been going on for a very long time. "It does appear to be a natural cycle," Landsea said. "We see evidence for this over the last several hundred years. It doesn't seem to be related to any possible greenhouse gas forming."

None of this means manmade global warming is not real. But some of what's happening is probably not connected to it at all.

Elspi wrote "It's not the melting but the warming that causes the rise in sea level. Heating a liquid causes it to expand."

This isn't accurate for water. Water actually expands ~10% upon freezing (due to the intermolecular forces known as hydrogen bonding). Upon melting it shrinks by ~10%.

However, the weight and also the volume of frozen water versus the liquid water will remain the same so an iceberg already surrounded by water won't change the overall volume of the ocean.

Run-off from land, however, will increase the volume of the ocean and affect ocean levels.

"We see evidence for this over the last several hundred years. It doesn't seem to be related to any possible greenhouse gas forming."
We do not have accurate or detailed storm information for the past one hundred years for starters, seems odd someone has evidence of “several hundred years” to back that statement. The broad spectrum data for any longer period would be sketchy, at best. And of course weather has cyclic patterns, as most natural phenomenon does, that has been understood for some time now.

Your understanding of water is incomplete. Water (at standard pressure) is the most dense at 4 degrees Celsius. As water gets colder and freezes it expands, as it gets warmer it expands. So the answer is yes, the ocean waters will expand as they are heated as long as the ocean water is warmer than 4 degrees celsius.

Re: the Gulf Stream. The predicted cooling caused by the slowdown of the conveyor belt (it's extremely unlikely to turn off altogether) will almost certainly be outweighed by the warming going on at the same time. It will still cause dramatic changes in climate and weather, but on average Britain and Western Europe won't be colder than now.

"It's not the melting but the warming that causes the rise in sea level. Heating a liquid causes it to expand."

I thought there might be a hitch in this, but it turns out you are essentially right.

Water is odd. It actually shrinks when it is warmed from 0-4 celsius, then expands with further heating. So, I wondered how much of the Earth's water exists in this temperature range. It turns out, 90% of the Earth's water is below the thermocline (in deep ocean denied sunlight), below 3 celsius.

I then wondered how pressure effects would figure in. Turns out, they exacerbate water's anomalous behaviour, so there would be even more shrinking due to warming. But, it was all for naught. Sea water behaves differently than fresh water. Sea water acts like most liquids and continuously expands with temperature.

Oh well.

I have always heard the statement "An iceberg floating in the sea won't raise sea levels for the same reason that an ice cube floating in a drink won't overflow the glass when it melts." However, isn't a large section of the iceberg also sticking above the water and not really effecting water levels? But if the entire berg melts, the water from this area is no added to the water column and would raise the water level...or am I missing something? I have heard the analogy about ice in your glass before but if those cubes were tall and stuck up above the water in the glass, and the water came to the rim of the glass, wouldn't water flow over the rim with the cubes melting?

Gore's point was that melting land-based ice will have a much greater impact on world sea levels than melting sea-based ice. He didn't discuss the effect of temperature on the overall volume of the ocean.

If you plop an ice cube into a beverage, the liquid level will rise because the ice cube is displacing liquid. However, the liquid level won't continue to rise as the cube melts.

The land-based ice isn't displacing any water. So, melting land ice is just the equivalent of pouring liquid into the glass. (Gore's metaphor for land-based ice was a stack of ice cubes resting on the bottom of a glass and piled high above the rim. If those cubes melted, you'd get overflow by the amount the volume of the frozen water exceeded the volume of the container.)

"It's not great art, but it's terrific science."

Do you judge science by it's conclusions, or by the methods used to reach conclusions?

Gore perfectly illustrates the old adage that a little knowledge is a dangerous thing.

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