e pur si muove

Barack Obama has made the official declaration just hours ago. Over 500 journalists, including representatives from 3 different Japanese networks, showed up in the frigid 0°F (-19°C) weather in Springfield, Illinois to be on the scene for the official word to be announced. Let the presidential campaigning begin!

I’m appalled at the dearth of coverage on this incredibly important issue. On Feb 2, the Intergovernmental Panel on Climate Change (IPCC) recently published a preview of their fourth report on the scientific evidence for anthropogenic (i.e. from human activity) causes of climate change. Shame on the media.

Why is the science of climate change so difficult to understand? The primary reason, I believe, is because climate change is trying to measure a very small signal amidst temperature fluctuations which are relatively much larger. People who claim that the record cold temperatures in the US since late January and the early blooming of cherry trees in DC disprove global warming are at best being facetious. The weather changes frequently on many time scales: day from night, winter from summer, El Niño and La Niña, and so on. What distinguishes these fluctuations from genuine climate change is that these changes are all cyclical¹. Climate change is about change on top of these cycles.

To this effect, a dead giveaway that there is some kind of force disturbing the equilibrium climate is if there is a sharp non-cyclical increase in any of the known mechanisms of climate change. To this effect the original report here [pdf] on page 2 contains the first punchline:

Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years (see Figure SPM-1). The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous oxide are primarily due to agriculture.

And what is this Figure SPM-1, you may ask? Well, here it is:²

Shocking, isn’t it? It looks from the data that there looks like some kind of weak cycle in the carbon dioxide and methane data with a period suspiciously close to 10,000 years. However each graph shows a huge spike in greehouse gas emissions in the past two centuries. I dare any reasonable person to deny that this graph shows that this fluctuation cannot be attributed to any expected change as a result of natural climate cycles.

The second punchline is that the radiative forcing (warming effect) of increase greenhouse gas emissions has been significantly masked by the cooling effect of particulate (aerosol) pollutants, mostly composed of sulphates, nitrates, carbon, and dust, and changes in surface reflectivity (and hence heat absorption) as a result of increased cloud cover and deforestation.³ So perhaps we shouldn’t be too quick to diss the Indonesian strip burning farmers; in their own way, they are trying to help combat global warming. But on more serious grounds, this also shows, paradoxically, that it is possible to hasten global warming by reducing particulate emissions from factories and vehicles. The report admits the scientific understanding on anything other than greenhouse gases is limited, but it also means that controlling climate change is not as simple as just reducing greehouse gas emissions.

The third key point is the conclusion that despite this and other confounding factors, the net effect of human activities since 1750 “has been one of warming”. Which means that we no longer have any scientific reason to doubt that industrial and post-industrial human civilizations have contributed directly to global warming.

The fourth punchline is that scientists have essentially figured out why sea levels are rising. In summary, the two major factors are

1. Thermal expansion. Hot water takes up more space than cold water. While this effect is usually so small as to be negligible in swimming pools and drinking glasses, this report states that the effect of heating 1,300,000,000 km³ of water in all the world’s oceans by even 1°C cannot be ignored.
2. Melting of surface ice. The physics of this almost trivial: give ice enough heat and it will melt. The report further subdivides the contributions of melting glaciers, polar ice caps and the ice sheets of Greenland and Antarctica as the most significant contributors.

The fifth key point is that scientists are now able to identify how climate change will directly affect the weather we experience. Table SPM-2 in the report summarizes the predictions, which is further summarized below. In general, places on land will experience:

1. less cold days and more hot days. D’oh!
2. more heat waves. Also d’oh!
3. more precipitation. This one may be puzzling, but think of the water cycle. Warmer oceans means more heat driving more water vapor into the atmosphere. Ergo, more rain.
4. more droughts. Does this contradict what they just said above? Not really. They’re trying to say that the average rainfall will increase, but when it stops raining, it will take longer for the next rain to come in any particular location.
5. more intense tropical cyclones. Katrina wasn’t a fluke.
6. higher extreme sea levels. What they said above.

In summary, global warming is real, and it is happening. Let’s do something about it before it gets worse.

Reference

1. Intergovernmental Panel on Climate Change (IPCC), Climate Change 2007: The Physical Science Basis -Summary for Policymakers [pdf]. Feb 5, 2007.

P.S. The report goes on to discuss the reliability of the various sources of data and forecast likely trends in climate change. I’m not too interested in these topics since they are really somewhat peripheral to the main point, but definitely read the report for more details.

1. Or at the very least, known weather cycles have periods of less than 10,000 years, which is the longest-time data set used in the study originating from ice-core studies.↩
2. The report has this footnote which I quote hence: “Radiative forcing is a measure of the influence that a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the factor as a potential climate change mechanism. Positive forcing tends to warm the surface while negative forcing tends to cool it. In this report radiative forcing values are for 2005 relative to pre-industrial conditions defined at 1750 and are expressed in watts per square metre (W m^-2).”↩
3. Interestingly enough, the data shows that the urban “heat island” effect is mostly local, and hence have negligible contributions to global warming.↩