Saturday, May 17, 2008

I got a bicycle. (Part II)

By Dustin Williams
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A man was speaking to my mom about climate change a few days ago. “What we’re seeing is simply natural climate variability,” the man said. “There’s no proof that we humans have anything to do with what’s happening.” My mom mentioned to him that I’m a meteorology graduate student and have told her that the evidence for human-induced (anthropogenic) climate change is pretty solid, to which he replied: “Well, your son is a meteorologist, not a climatologist.”

[Not sure what his implication was with the last comment. Meteorologists receive quite a bit of climate science education. Anyway, most climate science courses I’ve had, and the many climate science lectures I’ve attended, were conducted by what he calls “climatologists” who seem to think humans are in fact changing the climate.]

The man brought up a point that a lot of anthropogenic climate change skeptics like to make: The climate of the Earth is warming due to natural forces; we can’t stop it and shouldn’t put such a strain on our economies in an attempt to do so; and it’s naïve to even think that we humans could change our planet on such a large scale.

To which I say:

Wow! We never thought of that! We never thought to try to explain what’s happening with well-known, documented variations in the orbit, tilt, and “wobble” of our planet (also known as Milankovitch cycles)! We never thought to include the cycles of our Sun! And really, you don’t think 6.5 billion people are capable of royally screwing up our world?

All kidding aside, I do understand the position of some skeptics. To a degree, I’m a skeptic myself. Let me explain:

  • I believe that the science of radiative forcing (i.e., warming) due to greenhouse gases, in particular carbon dioxide, is proven science.
  • I believe that humans put a ridiculous amount of carbon dioxide into our atmosphere every day, most of which comes from the burning of fossil fuels; without us, nearly all of this carbon dioxide wouldn’t be released into the atmosphere. I think most people can agree this is true.


So, on a very fundamental level, I think humans should curb the amount of greenhouse gases we release into the atmosphere, simply because we know that they increase the amount of radiation absorbed by our atmosphere, and because the supply of fossil fuels on which we rely is on pace to disappear. This is a simple argument, but I don’t know how anyone can argue against it.

The point at which I become a skeptic is when viewing the predictions for how our climate will change due to what we’re doing. For the record, I don’t think climate change scientists have an agenda; I don’t think they hype climate change in order to receive attention or research money; in fact, I think climate scientists who advocate anthropogenic climate change are doing us all a favor, and are some of the few who actually give a shit about our planet.

With that said, though the models used to predict future climate are our best attempts, they have a lot of issues. A lot of the same physical processes in short-term weather prediction models are also in climate models, and we know how inaccurate weather prediction models can be. Most climate models are tuned to fit the past; that is, they’re designed to match the past climate in an effort to ensure that they’re handling physical processes correctly for future climate prediction. I think this is a useful procedure, but it involves a lot of approximation, and in some cases, adjusting numerical parameters (some that are completely non-physical) until the results are "better." But perhaps the biggest issue with climate models is how they handle water vapor. Water vapor is actually the most important greenhouse gas, and its affect on a warming climate is poorly understood. With warmer temperatures you have more evaporation and more water vapor in the atmosphere. With more water vapor you have more cloud cover and reflection of solar radiation, which in turn leads to a net cooling of the lower atmosphere. Does this cooling counteract the warming? Who knows. Also, with a warmer atmosphere, the circulations that drive our weather are shifted towards the poles, so the distribution of water vapor itself will change.

Throw into the mix:

  • Aerosols, which cause a very significant net cooling and have a much shorter life cycle in the atmosphere than carbon dioxide
  • Ice-albedo feedback, which means the surface of the planet absorbs more solar radiation with a decreasing amount of ice, which in turn leads to more warming and less ice (and again more warming, thus a “feedback”); climate models have actually been underestimating the amount of sea ice retreat in the Arctic
  • Changes in land use, which in some cases means releasing a huge amount of methane and carbon dioxide into the atmosphere (net warming), but also a decrease in the amount of solar radiation absorbed by the surface when clearing land since plants are “dark” and highly absorbent (net cooling)


There are many, many other things to consider (ocean circulations, upper-atmosphere circulations, sea level rise, etc.). The picture is quite complicated, and I honestly don’t believe that climate models accurately handle all these processes, some of which are in opposition.

So the question is, Do we prepare for the worst? I certainly think we should. Even if we’re unsure of what’s going to happen, all we need to do is take a look at what we’re doing right now to know that we’re having a large impact on the planet.

Ride those bicycles.

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