Wednesday, December 2, 2015

Sci-Am: Global Warming Not So Scary

Climate Change Will Not Be Dangerous for a Long Time
. . .In 1990 the Intergovernmental Panel on Climate Change (IPCC) was predicting that if emissions rose in a “business as usual” way, which they have done, then global average temperature would rise at the rate of about 0.3 degree Celsius per decade (with an uncertainty range of 0.2 to 0.5 degree C per decade). In the 25 years since, temperature has risen at about 0.1 to 0.2 degree C per decade, depending on whether surface or satellite data is used. The IPCC, in its most recent assessment report, lowered its near-term forecast for the global mean surface temperature over the period 2016 to 2035 to just 0.3 to 0.7 degree C above the 1986–2005 level. That is a warming of 0.1 to 0.2 degree C per decade, in all scenarios, including the high-emissions ones.

At the same time, new studies of climate sensitivity—the amount of warming expected for a doubling of carbon dioxide levels from 0.03 to 0.06 percent in the atmosphere—have suggested that most models are too sensitive. The average sensitivity of the 108 model runs considered by the IPCC is 3.2 degrees C. As Pat Michaels, a climatologist and self-described global warming skeptic at the Cato Institute testified to Congress in July, certain studies of sensitivity published since 2011 find an average sensitivity of 2 degrees C.

Such lower sensitivity does not contradict greenhouse-effect physics. The theory of dangerous climate change is based not just on carbon dioxide warming but on positive and negative feedback effects from water vapor and phenomena such as clouds and airborne aerosols from coal burning. Doubling carbon dioxide levels, alone, should produce just over 1 degree C of warming. These feedback effects have been poorly estimated, and almost certainly overestimated, in the models.

The last IPCC report also included a table debunking many worries about “tipping points” to abrupt climate change. For example, it says a sudden methane release from the ocean, or a slowdown of the Gulf Stream, are “very unlikely” and that a collapse of the West Antarctic or Greenland ice sheets during this century is “exceptionally unlikely.”

If sensitivity is low and climate change continues at the same rate as it has over the past 50 years, then dangerous warming—usually defined as starting at 2 degrees C above preindustrial levels—is about a century away. So we do not need to rush into subsidizing inefficient and land-hungry technologies, such as wind and solar or risk depriving poor people access to the beneficial effects of cheap electricity via fossil fuels.
More or less my position on global warming. Yes, CO2 is increasing, yes CO2 is a greenhouse gas, but empirically, warming has not increased as fast with CO2 rise as the models predict. When the models disagree with the data, fix the models, not the data (as the warmists have been wont to do).

And, if necessary, mankind can fix it more rapidly than the catastrophists have warned, because the lifetime of CO2 in the atmosphere is much shorter than they have stated: CO2 residence time said to be 40 years, not 1000 per previous claims
Surplus CO2 is removed from the atmosphere by natural sinks at rate, proportional to the surplus CO2 concentration. In other words, it undergoes exponential decay with a single decay constant. This conclusion is rigorously proven, using first principles and relatively recent observations of oceans. Historical data for CO2 concentrations and emissions from 1958–2013 are then used to calculate the half-life of the surplus concentration. This theoretically derived formula is found to be an excellent match to the historical CO2 concentrations over the measurement period. Furthermore, the “initial” CO2 concentration in the formula came out to be very close to the likely “pre-industrial” CO2 concentration. Based on the used datasets, the half-life of the surplus concentration of CO2 in the atmosphere is found to be approximately 40 years.
If stabilizing or decreasing atmospheric CO2 content becomes desirable at some point in the future, that can be achieved by decreasing anthropogenic CO2 release at that time; no premature action is needed.

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