I was really impressed by this picture when I first saw it. It is from the NASA website and shows the extent of warming in the Arctic relative to the rest of the globe.
An American newspaper included comment that:
A University of Alabama scientist says global warming is not nearly as global as some people think. …Temperatures in 2005 followed a general pattern seen since 1978, with the most significant warming seen in the northernmost third of the planet. Large regions of slightly warmer than normal temperatures covered much of the globe.
The Arctic atmosphere, however, has warmed more than seven times faster than that over the southern two-thirds of the globe.
And there was comment at Tim Blair’s popular blog along the lines:
The carbon dioxide from fossil fuels is distributed pretty evenly around the globe and not concentrated in the Arctic, so it doesn’t look like we can blame greenhouse gases for the overwhelming bulk of the Northern Hemisphere warming over the past 27 years
Vincent Gray has written that:
The models predict increased warming, equally, at both the North and South Poles. The measurements show that the two poles are completely different. The North Pole is warming the South Pole is cooling.
The models predict much greater warming than is observed, and the only way they can get out of it is to assume a large cooling influence of clouds and aerosols, Since these are concentrated in the Northern Hemisphere, there should be greater net warming in the South than in the North. The observations show the opposite.
But, according to Cecilia Bitz writing for Real Climate the models can, and do, account for lots of warming at the Arctic and not much at the Antarctic:
Manabe and Stouffer (1980) first popularized the phrase “polar amplification” to describe the amplified rate of surface warming at the poles compared to the rest of the globe in their climate model’s response to increasing greenhouse gas levels.
Their early climate model had a simple ocean component that only represented the mixed layer of the water. Their model had roughly symmetric poleward amplification in the two hemispheres, except over the Antarctic continent, where they argued the ice is too thick and cold to melt back.
…Observed polar climate change from the instrumental record is not symmetric. Except along the Antarctic Peninsula , most evidence of significant warming is from the Arctic. In addition, total sea ice extent in the Southern Ocean has had no significant trend since satellites began taking data in 1979 (Cavalieri et al 2003). Newer climate models generally also have very modest or no polar amplification over the Southern Ocean and Antarctica in hindcasts of the last century. The presence of a deep and circulating ocean component is key because ocean heat uptake increases most in the Southern Ocean as the climate warms (see Gregory 2000). The asymmetry at the poles does not however result from a difference in feedback strength associated with the ice or atmosphere. In fact, when these same climate models are run to equilibrium (in the same way that Manabe and Stouffer ran their model so that ocean heat uptake is not a factor) the hemispheres have nearly equal polar amplification.
David Jones at the Australian Bureau of Meterology explains:
The failure of the Antarctic to warm is pretty well understood. It is linked to the marked strengthening which has occurred in the southern annular mode. The “southern annular mode” is a fancy name for the strength of the Antarctic low pressure trough and westerly winds (the roaring forties, furious fifties, screaming sixties).
… Over the last 30 years we have seen a very marked intensification of the trough – most of this happened in a short period of time from around 1970 to 1990. This is believed to be due to the loss of ozone in the polar stratosphere which caused a very strong cooling of the stratosphere and upper troposphere over the Antarctic. This cooling lead to a strong increase in the temperature gradient between the equator and poles, which through the dynamics must strengthen the westerly winds (this is summarised in a fairly basic dynamical equation called the “thermal wind” relationship).
The strengthened westerlies has a number of effects. These include enhanced warming on the northern side of the trough (the trough typically being near 65S). This explains the spectacular warming over the Antarctic Peninsula (which is occurring much faster than one might expect from the simple greenhouse effect). On the southern side, the reverse happens; i.e. cooling.
For the last 20 years of so, this cooling has been sufficient to offset the enhanced greenhouse effect. This is a great example of the thermodynamics (temperature changes) and dynamics (winds etc) operating in different directions. Another effect of the stronger westerlies is that the increase the equatorwards drift of sea ice (through a process called Ekman drift) which probably explains why sea ice in the southern hemisphere appears to have retreated extensively from around 1900 to 1970 and stabilised and infact expanded subsequently.
There is a real cautionary tale here about non-linearities in climate change.
There is, in my view, also a real cautionary tale in the new paper by Keppler et al. in science journal Nature as summarized in the Editorial:
The unexpectedly high levels of the green-house gas methane over tropical forests, and the recent decline in the atmospheric growth rate of methane concentrations, cannot be readily explained with the accepted global methane budget. Now a genuinely surprising discovery provides a possible explanation for these phenomena, and may have implications for modelling past and future climates. It was thought that methane formed naturally only in anaerobic conditions, in marshes for instance. In fact living plants, as well as plant litter, emit methane to the atmosphere under oxic conditions. This additional source of methane could account for 10-30 percent of the annual methane source strength and has been overlooked in previous studies.
Vincent Gray has remarked with respect to this new finding that:
The answer to the fact that climate models cannot simulate actual global temperature change may be due to a fact I have been emphasizing for many years. The models all assume that greenhouse gases are “well-mixed”, however, they are not “well-mixed”, so that temperatures cannot be adequately calculated by using average greenhouse gas concentrations. You should use actual concentrations over the particular region.
… Of course, average methane concentrations in the atmosphere have apparently stabilised, so this present scare does not add any extra greenhouse gases to the atmosphere. It does cast into serious doubt current models supposedly relating emissions of methane to atmospheric concentrations, though.
This discovery will certainly change attitudes to “climate change”, for it now appears that in order to reduce “global warming” you should not only cut carbon dioxide emissions, but you should also cut down forests, reduce agriculture, drain wetlands and cover the world with concrete.
Rather than “cover the world with concrete” as concrete is also a source of greenhouse gases, there is perhaps reason at this time in our history for both global warming skeptics and global warming believers to be a bit humble. There is so much we just don’t understand.
But someone, tell me how important is it really, as Vincent suggests, that we “use actual concentrations over the particular region”?