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.