It's been a temperate summer in much of North America. So does that mean global warming is over? Not by a long shot.

From The Tyee (posted Sept. 9):

It's true that 2008 has been a colder-than-we're-used-to (lately) year for North America. In fact, there is a good chance that the next few years will be much like it. But it's not because the laws of thermodynamics have suddenly changed.

One cold, wet summer -- or even several in a row -- does not mean global cooling has begun. Deluding ourselves into thinking it has would be dangerous indeed. Especially so on the eve of an election that may turn on Canada's climate strategy.

What such reports overlook is that global surface temperature estimates are based overwhelmingly on observations of air temperature. As a matter of physics, the atmosphere holds relatively little of the extra heat building up inside Earth's greenhouse-gas shell.

Most of that heat is being absorbed into the oceans (accounting, incidentally, for about half the rise in ocean levels worldwide, as warmer water molecules expand). But science has relatively few tools for measuring ocean temperature, or factoring the heat stored there the average global temperature.

The oceans themselves are big places, and not uniform. Sometimes warmer water sits on top of a cooler mass (a description of the El Niño phenomenon in the eastern Pacific). Sometimes colder water covers the surface (La Niña). Whichever one is uppermost has much more impact on the easily influenced surface air temperature and current weather over the continents, than does the heat absorbed and temporarily locked away in submerged ocean layers. ...

Sooner or later, that heat will out. And when it finally does break out into the near-surface atmosphere where weather happens and we live, its effect will be like the elastic we've stretched to the limit and released: too likely to snap us in the eye.

That snapback moment will come, British scientists calculate, around the middle of the coming decade.

What then?

When these huge sea-cycles perform their next oscillation, as they must, and begin to pass all the heat energy that's been stored up temporarily in the deep or tropical oceans through to North America, we will get to experience new categories of extremes at the other end of the scale: exhausting series of droughts and scorching heat-waves.