Tuesday, February 25, 2014

How Much Warming Since 1950? This Much.

From last week's Science magazine, from Gabi Hegerl and Peter Stott:

This says that internal variability, which Judith Curry likes to emphasize, is only about 1 part in 6.


J Melcher said...

On the basis that one can never ask too many questions, I wonder how large a role may be played by soot -- layered atop Arctic ice and changing albedo? Soot and CO2 emissions from coal fired industries have for most of a century been inextricably linked. A mindless correlation chart comparing coal consumption and temperature, therefore, would show -- perhaps correctly -- that as emissions rose, so did temperature. A more carely constructed chart would ALSO show that as "scrubbers" became more common in the 1970s the emissions of soot and CO2 diverged even as the consumption of coal continued along "business as usual".

A naive observer might also wonder whether soot production, most of which occurs in the northern hemisphere, might impact the Arctic more strongly than the Antarctic. What is the trend in sea ice, in each of the two locales? Is there another hypothesis for why one pole might react differently from another, given the same well-mixed atmospheric forcing?

And which is the more easily remediated problem -- reducing soot, or reducing CO2? For example, if the Chinese or Indian governments agreed to meet US or German particulate emission standards, but continued to refuse to meet Kyoto-based CO2 emission standards, would that be helpful in reducing uptake in darkened near-Arctic regions? This particularly as natural snow begins to cover the last decades' deposit of soot, dust, fly ash, etc?

One might go on to wonder about other anthropogenic forcings such as deforestation, over-grazing, over-fishing, oil-slicks, war-related environmental destruction (the fires of Kuwait in 1991) or for that matter post-war environmental restoration (the return of the "Marsh-Arabs" in Iraq in the 2000's). One can easily accept that humanity and human civilization impact the climate while still vigorously denying the wisdom of government reliance on overly simplistic models that treat one particular trace gas as the be-all and end-all "control knob".

Dano said...

Mr Melcher, we know that there are forcings in addition to CO2.



Paul S said...

J Melcher,

Measurements of black carbon/soot in the Arctic (from the 2013 Arctic Report Card) indicate decreasing amounts in that region. As you suggest when you talk about "scrubbers" this kind of trend is expected given changing practices and technologies designed to reduce particulate emissions in many European countries and in North America. Not sure why you would still conclude that soot might be an important factor for Arctic sea ice losses over the past few decades given those reductions?

There have been numerous discussions about climate change mitigation strategies focusing on black carbon and methane in the short term. The upshot has been that actually the case for such a focus is pretty weak overall. Part of the issue is co-emittors from the same sources which induce oppositional climate forcing, so if you act to reduce black carbon emissions in most cases you will also reduce emissions of factors which cause cooling, meaning the overall effect is minimal. There is however a case to be made on health grounds.