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The Science of Climate Change

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The latest issue of Scientific American has a informative article on the current state of climate science: why we know the earth is warming, and why we know human activity is partly to blame.

The authors are William Collins of UC-Berkeley; Robert Colman, an Australian; James Haywood of the UK's Met Office; Martin Manning of NOAA; and Philip Mote, the climatologist for the state of Washington.

Unfortunately it'll cost you $5 to read the article online. I'll summarize the key points here, but if you want to read the whole article you'll need to buy a copy or go to the library.

The main points:

Greenhouse Gases
Atmospheric concentrations of carbon dioxide, methane and nitrous oxide have been stable for 10,000 years — until they began growing rapidly about the time the Western world industrialized.

Warming
1. 11 of the past 12 years are the warmest since reliable records began around 1850. That's a pretty short time frame, geologically speaking, but the probability of that happening by chance are very small.

2. Measurements from ice cores and tree rings provide a longer time line, showing that the current climate is warmer than it has been for at least 1,300 years.

3. While natural variability occurs, temperature extremes have changed in accordance with the warming trends. Frost days and cold days have become less common, while heat waves and hot days have become more common.

4. The oceans are warming as well, more so at the surface than in the depths, a sign that the warming source is at the surface.

5. Overall, the planet's average temperature has risen .75 degrees Centigrade (about 1.5 degrees Fahrenheit) in the last 100 years — and the pace is accelerating.

Rising Sea Levels
1. The oceans have absorbed more than 80 percent of the added heat. This has warmed the water, which expands, causing sea levels to rise. Melting glaciers and ice sheets add to the effect.

2. The oceans have been measured rising an average of 3.1 millimeters a year. Over 50 years, that would mean a total increase of 155mm, or about 6 inches. The process is expected to accelerate, however, for a total rise in the 21st Century of maybe 40 centimeters (400mm, or about 16 inches) and possibly as much as 60 centimeters (about two feet).

3. With rising sea levels comes inundation of low-lying coastal areas, a higher water table, increased flooding, erosion, salinization of coastal waterways and wetlands, and greater danger from storms. An EPA study of the effects of various levels of sea rise suggests (while admitting it is an underestimate) that even a 6-inch increase would cost the United States alone something like $100 billion if we wanted to protect developed coastal areas and prevent inland flooding. That cost would be spread over 100 years, so the annual cost isn't too bad and assumes coastal development all but ceases, and that sea levels stop rising. The costs rise fairly rapidly with additional increases in sea levels.

Human Causes
We know humans are responsible for much of this increase for several reasons.
1. Some greenhouse gases, like halocarbons, have no natural sources.

2. Geographic differences in concentration comport well with human causation, with heavier concentrations over the more heavily populated and industrialized northern hemisphere.

3. Analysis of isotopes in atmospheric gas can identify the origin of the gas. It turns out most of it comes from burning fossil fuels.

4. There is more warming over land than over sea, and in the ocean the greatest warming is occurring at the surface — both indicators of a human factor.

5. The troposphere (the lower atmosphere) is warming while the stratosphere is cooling — exactly what you would expect if the cause was increased emissions of greenhouse gases and depletion of stratospheric ozone. If warming was primarily caused by solar activity, both layers of the atmosphere would warm up.

Measurment Accuracy
1. For the long-lived greenhouse gases, we know their heat-trapping effects fairly well, because we have precise measurements of their concentration and distribution in the atmosphere, and we know how they affect the planet's energy balance.

2. Five years have passed since the last major report, and in those five years temperature increases have been consistent with projections of greenhouse-driven warming.

3. The climate models used to make predictions and measure the effects of various warming and cooling factors are getting better. In addition, results are drawn from an ensemble of 18 modeling groups, so the weakness of any single model can be identified and its effect on conclusions reduced.

The article ends with a discussion of what isn't known, the limitations of current research and thus the lack of granularity in some areas. But overall I think it does a good job of explaining why leading scientists think humans are a significant factor in global warming.

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About Sean Aqui

  • stuart

    I will have a read of the article – but until it will take me some convincing that the analysis put forward in the paper at the following link is not more on the money.
    Skeptics Guide to Anthropogenic Global Warming

    The arguments for why I believe there should be no consensus at this stage are laid out well in the linked paper. I suggest people read it and make up their own minds.

    cheers
    stuart

  • http://yesteryearmuseum.blogspot.com Doug DeLong

    What is it with global warming skeptics?

    If scientists were to tell us that there’s a giant meteor heading for earth, and unless we act now it will destroy the planet, would skeptics say, “I don’t believe you?”

    Wouldn’t it be more prudent, even if you’re not 100% convinced, to assume that the scientists know what they’re talking about? I mean, wouldn’t you want to play it safe?

    Of course, I have a feeling that many of the global warming skeptics are the same people who think evolution is “just a theory” and they’re probably not truly convinced that the earth revolves around the sun.

    For them, global warming is just another liberal plot which will inevitably lead to gay marriage and the outlawing of guns.

  • troll

    100 billion seems cheap

    Doug asks – *What is it with global warming skeptics?*

    it’s pretty clear that their beef is with folks who claim that they have a clue concerning what to do about it…about how to spend the money – allocate the resources

    the more extreme among them ‘see’ scientists being bought by an international socialist cabal which wants to see the US brought down a few notches

    ‘doing science’ is a political activity isn’t it – ?

  • http://www.thechurchofanswers.com Heloise

    This recent article also points up why Gore is more of a phony than first thought. If this and more has been going on–where was Gore when he was in power, in office?

    Everyone will have to be diligent when it comes to energy conservation. It seems no one is listening or reading.

    Heloise

  • Alec

    Doug DeLong — RE: Wouldn’t it be more prudent, even if you’re not 100% convinced, to assume that the scientists know what they’re talking about? I mean, wouldn’t you want to play it safe?

    Well, no, not necessarily. Global warming alarmists are demanding that huge amounts of money be spent and huge amounts of resources re-allocated to “solve” a problem that might occur 100 years in the future. There is already a veneer of elitism about this, as comfortable people in the West demand that money that could be used to battle diseases that are killing people in Africa and Asia today be used instead to make sure that some tree hugger in Malibu feel important.

    At best, scientists can help point out issues that need to be addressed, but when they pretend to be economists or politicians, they are stepping into areas that they know nothing about.

    The other problem here is that a number of short term predictions regarding global warming have not turned out to be correct, sending scientists to adjust the models on which global climate change are based. I don’t know about you, but I cannot blindly accept the claims of people who insist that their long term predictions are correct even though their short term — verifiable — claims don’t pan out.

    RE: Of course, I have a feeling that many of the global warming skeptics are the same people who think evolution is “just a theory” and they’re probably not truly convinced that the earth revolves around the sun.

    Actually, many global warming skeptics (like me) are hard core agnostics or atheists. Others are libertarian, but don’t have any particular religious axe to grind. On the other hand, many global warming alarmists know absolutely nothing about science or economics, are anti-technology, and have a feverish dream that human beings can return to some mystical, spiritual state of nature in which technology either doesn’t exist or is in perfect harmony with Mother Earth.

    Many of these people are just as bad as the most ignorant creationists.

  • http://www.PhotoshopTodaynet.blogspot.com/ T. Michael Testi

    If scientists were to tell us that there’s a giant meteor heading for earth, and unless we act now it will destroy the planet, would skeptics say, “I don’t believe you?”

    If the reason for the meteor was because of overpopulation and that increased the gravity of the earth was sucking the meteor toward us. So to save the earth we must eliminate 50% of the world’s population. I would be a skeptic!

    I don’t arguing global warming; the argument is that man has caused it and even more importantly that we can fix it by spending money.

    Remember there is global warming on Mars as well and the last I checked the only thing that we had up there were electric robotic rovers.

    T.

  • http://midtopia.blogspot.com Sean Aqui

    Why are y’all arguing generalities rather than address the specific points outlined in the article?

  • Alec

    Sean Aqui – RE: Why are y’all arguing generalities rather than address the specific points outlined in the article?

    I’m still digesting the Scientific American article. By the way, the current (July/August 2007) issue of the magazine “Skeptical Inquirer,” also has an article about global climate change which concludes with the following bold statement: “No scientist to date has made a strong case … for any observation(s) or mechanism(s) that can explain the current rapid global-warming trend by invoking natural causes.

    That said, any prediction that global climate change will lead to global catastrophe 100 years from now unless we do … something … is STILL little more than speculation. Also, recent detailed observations are revealing critical weaknesses in climate models. For example, a very recent BBC news story that the Arctic regions quickly turned into a tropical hothouse millions of years ago notes the following:

    “The [ice] core revealed that before 55 million years ago, the surface waters of the Arctic Ocean were ice-free and as warm as 18C (64F).

    But the sudden increase in greenhouse gases boosted them to a balmy 24C (75F) and the waters suddenly filled with a tropical algae, Apectodinium.

    When current climate models were applied to this period of the Earth’s history, said Dr Sluijs, they predicted North Pole temperatures to be about 15C (27F) lower than the core shows. ”

    The full story can be found here

    The news story contains this caution: “Appy Sluijs points out that the data reveals that some of the climate models used to detail the Arctic’s history got things wrong; and, as they are the same models that predict our future climate, they may need adjusting.”

    So, to my mind, the most parsimonious observation is that human activity contributes to global climate change. Whether or not this is good or bad, or even significant in any material sense, remains to be seen.

  • http://midtopia.blogspot.com Sean Aqui

    Alec: Thanks for the on-point reply. I think the criticism of the models is the strongest one available to skeptics. But that’s a debate over what effects the warming might have. The fact of the warming, and humanity’s significant role in it, seem well-established — and yet there are still people who deny both (the latter more than the former).

    One wonders why anyone gives credence to people whose positions over time have been:

    1. Global warming is a myth;

    2. Okay, warming is real, but the causes are natural, not anthropogenic.

    3. Okay, there are some human causes, but they’re not significant.

    4. Okay, they’re significant, but the effects will either be minor or can’t be known.

    Any one of those positions, at any given time, might have been reasonable (if expressed as questions, not as positive assertions). But anyone who has held all four of them should be dismissed as uncredible.

    So, to my mind, the most parsimonious observation is that human activity contributes to global climate change. Whether or not this is good or bad, or even significant in any material sense, remains to be seen.

    Agreed. But while that may be a reason to avoid spending hundreds of billions of dollars immediately, it’s not a reason to ignore it, or to avoid taking what reasonable steps we can to reduce emissions.