Global warming is for real. Even the most skeptical climatologists subscribe to the basic notion that man has pumped so much carbon dioxide into the atmosphere that the planet has and will continue to warm.  However they do not agree on how much the planet will warm as a function of atmospheric CO2 – and the range of values is as large as the chasm between best and worst case scenarios.

Some models assume the climate to be very sensitive to CO2 levels, while others assume much less sensitivity. A simple value that’s commonly used to compare sensitivities among models is the amount of warming that ensues from a doubling of atmospheric CO2. (Mankind has thus far jacked atmospheric CO2 by more than 40% over pre-industrial levels, to its highest concentration in several million years, since before our species existed. Doubling is expected to occur during the 2050s.)

At the low end are models predicting that doubling atmospheric CO2 will yield an increase in average planetary surface temperature of 1 to 1.5 C degrees. That kind of warming would be inconvenient, not disastrous – assuming, of course, that mankind succeeds only in doubling CO2, not trebling it, which is quite possible given current emissions. At the other end of the spectrum are climate models predicting a 6 to 7 C degree increase for the same doubling. This isnt merely a death sentence – it means we’re dead already: the CO2 we’ve already released will inexorably wreck our civilization-friendly biosphere no matter what we do.

How does one pick and choose among these different climate models? A clever answer to that question may win you a Nobel. While many models converge on a sensitivity of about 3 C degrees, it’s not at all clear that the true value should be near the mean or median. But lacking a better criterion for judgement (only climatologists can judge individual models on their merits), we would suggest that a sensitivity of 3 C degrees is a reasonable basis for making public policy prescriptions – leaving open the real chance that the actual value may be much higher or lower. That level of sensitivity should motivate us to act on global warming without delay. An increase in mean surface temperatures of just 2 C degrees may prove disastrous. A 3 degree increase will end life as we know it.

The catch is that cutting CO2 is not costless. Cheap energy has lifted hundreds of millions out of poverty in India and China, and stands to lift hundreds of millions more. The developed West has much less at stake in terms of human misery, and their economies are far less energy intensive. Thus it’s reasonable that the developed and developing worlds should approach global warming differently. Aggressively cutting back emissions is far more attractive to western countries on a simple cost-benefit analysis. The developing world, by comparison, can reasonably tolerate higher emissions in pursuit of faster growth.

This leads us to another strategy to approach global warming: do nothing, except grow the world economy with cheap energy, and hope that future generations, with their higher incomes and superior technology, will be better able to manage the mess we leave them. Consider how primitive technology from the year 1915 looks to us today. Given that the pace of innovation is increasing, 2015 will look even more primitive to the people of 2115. Problems that are incurable to us may not be so daunting to them. It may be that the best gift we can make to future generations is greater wealth, technology and productivity – not lower CO2 levels.

Of course wealth and climate change are not independent – a rapidly changing climate will impoverish future generations, as they are forced to divert resources to deal with crop failures and rising seas. Likewise, cutting emissions too aggressively will undermine economic growth, leaving millions in poverty, and robbing future generations of the means to cope with whatever problems they face.

Modeling climate is a tricky business. Guessing at what generations 50 and 100 years hence might be capable of is even harder. While global warming is a real problem, the best approach is not at all clear. We have options, and must pay careful attention as new facts arrive, to plot our best course for the future.

 

Editor’s note: Reluctantly, effective next week, the Field Guide is cutting back to one post weekly, to make time for other projects. Sincere thanks to the LFG faithful – we hope to return to twice or thrice weekly by the end of the year.

 

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Refs:

Views on climate sensitivity:

http://en.wikipedia.org/wiki/Climate_sensitivity

http://en.wikipedia.org/wiki/IPCC_Fifth_Assessment_Report#Climate_change_2013:_report_overview

http://www.scientificamerican.com/article/ipcc-revises-climate-sensitivity/

http://www.skepticalscience.com/climate-sensitivity-advanced.htm

http://www.nytimes.com/2013/05/14/science/what-will-a-doubling-of-carbon-dioxide-mean-for-climate.html?_r=0

http://www.weeklystandard.com/articles/what-catastrophe_773268.html?page=3

How hot is too hot:

http://www.newrepublic.com/article/119757/two-degrees-climate-change-no-longer-possible

http://www.livescience.com/17340-agu-climate-sensitivity-nasa-hansen.html

What a future cure may look like:

http://en.wikipedia.org/wiki/Carbon_dioxide_removal

http://www.technologyreview.com/featuredstory/531346/can-sucking-co2-out-of-the-atmosphere-really-work/

or not:

http://www.technologyreview.com/view/516166/what-carbon-capture-cant-do/