Further Comments on The Economist's Take on Climate Sensitivity
Posted on 11 April 2013 by dana1981
Last month, The Economist published an article about climate sensitivity – how much the planet's surface will warm in response to the increased greenhouse effect from a doubling of atmospheric CO2, including amplifying and dampening feedbacks. We responded with some brief comments and critiques at the time. Today two relevant and more in-depth articles on the subject were published, and are excerpted here.
ABC Environment, 12 Apr 2013
A recent news article suggested that climate change may not be as bad as feared. But the report was based on one flawed study and missed a lot of important points.
The Economist recently published a lengthy article about Earth's climate sensitivity — how much the planet's surface will warm in response to the increased greenhouse effect if the amount of carbon dioxide in the atmosphere doubles relative to pre-industrial levels (something that will happen in a matter of decades if we continue with business-as-usual fossil fuel burning).
While we are pleased that The Economist brought attention to this important topic, we were disappointed by the shortcomings and inaccuracies in the piece with regard to the current state of scientific understanding.
The article focused heavily on claims that the slowed warming of Earth's surface in recent years implies a dramatically lowered estimate of climate sensitivity. The claim was primarily supported by a single as-yet unpublished article by a group in Norway, which attempts to use instrumental temperature evidence available back through the late 19th century to estimate the climate sensitivity. The authors of that article conclude that use of data to the year 2000 yields a climate sensitivity of 3.9°C, which is at the high end of the generally accepted 2 to 4.5°C range. Yet they find that by including just an additional decade of data (i.e. using observations available through 2010), the estimate falls by nearly half, to 1.9°C.
It should be a red flag that an estimate of climate sensitivity would change by a factor of two based only on the addition of a decade of data. In reality, the climate sensitivity now is not half what it was a decade ago. So where did the Norwegian study go wrong?
A recent article in The Economist stated that “over the past 15 years air temperatures at the Earth’s surface have been flat while greenhouse-gas emissions have continued to soar.” The Economist went to great lengths to point out that “the mismatch between rising greenhouse-gas emissions and not-rising temperatures … does not mean global warming is a delusion.” But the piece was predictably lauded by climate skeptics as “further evidence” of the case against climate change.
Except that … it wasn’t.
As The Economist piece itself pointed out, this wasn’t an argument that “global warming has ‘stopped.‘” The past two decades have been the hottest in recorded history; of the nine hottest years on record, eight have come since 2000. The question, though, is why the year-on-year/decade-on-decade increase appears to have been somewhat less in the past 10 to 15 years, given the ongoing increase in atmospheric greenhouse gas concentrations.
To which there are several answers.