Tuesday, September 17, 2013

Rethinking Global Warming

There's an interesting piece on global warming at the WSJ by Matt Ridley. It turns out that an important report by the IPCC (Intergovernmental Panel on Climate Change) due to be released in a week or so will reveal that earlier predictions of "hockey stick" shaped graphs depicting skyrocketing temperature increases are mistaken, and the alarms sounded by the Al Gores of the world are overwrought. It even suggests that the climate change that is occurring may be on balance beneficial, a possibility we've wondered about at VP on a number of occasions.

Here's part of what Ridley says:
The big news is that, for the first time since these reports started coming out in 1990, the new one dials back the alarm. It states that the temperature rise we can expect as a result of man-made emissions of carbon dioxide is lower than the IPPC thought in 2007.

Admittedly, the change is small, and because of changing definitions, it is not easy to compare the two reports, but retreat it is. It is significant because it points to the very real possibility that, over the next several generations, the overall effect of climate change will be positive for humankind and the planet.
Ridley follows this with a bunch of numbers which the interested reader can read for him or herself, but then there's this:
A more immediately relevant measure of likely warming has also come down: "transient climate response" (TCR) — the actual temperature change expected from a doubling of carbon dioxide about 70 years from now, without the delayed effects that come in the next century. The new report will say that this change is "likely" to be 1 to 2.5 degrees Celsius and "extremely unlikely" to be greater than 3 degrees.

Most experts believe that warming of less than 2 degrees Celsius from preindustrial levels will result in no net economic and ecological damage. Therefore, the new report is effectively saying (based on the middle of the range of the IPCC's emissions scenarios) that there is a better than 50-50 chance that by 2083, the benefits of climate change will still outweigh the harm.

Warming of up to 1.2 degrees Celsius over the next 70 years (0.8 degrees have already occurred), most of which is predicted to happen in cold areas in winter and at night, would extend the range of farming further north, improve crop yields, slightly increase rainfall (especially in arid areas), enhance forest growth and cut winter deaths (which far exceed summer deaths in most places). Increased carbon dioxide levels also have caused and will continue to cause an increase in the growth rates of crops and the greening of the Earth—because plants grow faster and need less water when carbon dioxide concentrations are higher.

Up to two degrees of warming, these benefits will generally outweigh the harmful effects, such as more extreme weather or rising sea levels, which even the IPCC concedes will be only about 1 to 3 feet during this period.
Ridley notes that even the reduced expectation of increasing temperature in the IPCC report may be too high. Other reports point to even milder warming than forecast by the IPCC report. All of which is to say that there's reason to be cautious in forming opinions about the severity of the threat we face. Indeed, those who only a year or two ago were calling any climatologist who was skeptical of Mr. Gore's dire predictions the equivalent of a terrorist who should be fired or otherwise censored have been a bit muted lately. And for good reason:
It is now more than 15 years since global average temperature rose significantly. Indeed, the IPCC chairman Rajendra Pachauri has conceded that the "pause" already may have lasted for 17 years, depending on which data set you look at. A recent study in Nature Climate Change by Francis Zwiers and colleagues of the University of Victoria, British Columbia, found that models have overestimated warming by 100% over the past 20 years.

Explaining this failure is now a cottage industry in climate science. At first, it was hoped that an underestimate of sulfate pollution from industry (which can cool the air by reflecting heat back into space) might explain the pause, but the science has gone the other way — reducing its estimate of sulfate cooling. Now a favorite explanation is that the heat is hiding in the deep ocean. Yet the data to support this thesis come from ocean buoys and deal in hundredths of a degree of temperature change, with a measurement error far larger than that. Moreover, ocean heat uptake has been slowing over the past eight years.

The most plausible explanation of the pause is simply that climate sensitivity was overestimated in the models because of faulty assumptions about net amplification through water-vapor feedback. This will be a topic of heated debate at the political session to rewrite the report in Stockholm, starting on Sept. 23, at which issues other than the actual science of climate change will be at stake.
By this Mr. Ridley is suggesting that what comes out of Stockholm may very well be a product more of the ideological and political aspirations and predilections of those who draft the report than of the empirical data that climatologists are coming up with.