Global Warming is not over, actually, but this is the kind of title I've been seeing floating around the internet over the last several days. It's not a new statement from the skeptic camp, but rather one that gets a new life every now and again, when a scientifically challenged media outlet decides to hand the mouthpiece to someone without first checking the facts.

In this latest flurry, the 'someone' is Jennifer Marohasy, a fervent advocate of free market policies and Director of the Environment Unit at right-wing Australian think tank the Institute of Public Affairs (a benign sounding name for an institution that was apparently "born out of frustration with the current direction of environment groups"). Talking on Australia's ABC National Radio with Michael Duffy, the dialog would be amusing if it wasn't for the fact that many people will actually read and believe it.

The argument presented is that since 1998 global temperatures have plateaued.

Duffy asked Marohasy: "Is the Earth still warming?"

She replied: "No, actually, there has been cooling, if you take 1998 as your point of reference. If you take 2002 as your point of reference, then temperatures have plateaued. This is certainly not what you'd expect if carbon dioxide is driving temperature because carbon dioxide levels have been increasing but temperatures have actually been coming down over the last 10 years." -- The Australian

Annual surface temperature anomaly relative to 1951-1980 mean - tracking up to Nov 2007

But, before you go back to sleep on all things global warming, consider the following:

1998 was, indeed, particularly hot. One of the main contributing factors to this record-breaking year was a very strong El Niño event -- an El Niño that some regard as the strongest of the last century, and one that destroyed an estimated 16% of the world's coral reef systems (Wikipedia).

1998 broke the previous record (which was held by... ahem... 1997) by a full 0.2'C (it doesn't sound like much, but when looking at global averages it is actually very significant). But, take a look at the graph above, from this NASA report, and you start to get a clearer picture of what's going on.

1998 was yet another peak in a succession of peaks. If you were to simplistically take only the last ten years into consideration, then Jennifer's conclusions could have some merit, but when you look at long term trends (as legitimate scientists must) then you discover a very different reality.

In addition, while some studies conclude that 1998 still holds the record for hottest year, NASA indicates that 2005 broke that record, and did so without the aid of an El Niño event:

Climatologists at NASA's Goddard Institute for Space Studies (GISS) in New York City noted that the highest global annual average surface temperature in more than a century was recorded in their analysis for the 2005 calendar year.

Some other research groups that study climate change rank 2005 as the second warmest year, based on comparisons through November. The primary difference among the analyses, according to the NASA scientists, is the inclusion of the Arctic in the NASA analysis. Although there are few weather stations in the Arctic, the available data indicate that 2005 was unusually warm in the Arctic.

... Previously, the warmest year of the century was 1998, when a strong El Nino, a warm water event in the eastern Pacific Ocean, added warmth to global temperatures. However, what's significant, regardless of whether 2005 is first or second warmest, is that global warmth has returned to about the level of 1998 without the help of an El Nino.-- NASA

The studies that hold that 1998 is still the record-holder do so by excluding Arctic temperature records. We must keep in mind that the arctic regions are warming faster than anywhere else, so their exclusion removes critical warming data.

Furthermore, last year, 2007, tied with 1998 to become the second warmest year on record, behind 2005, and this despite a cooling El Niña event.

The year 2007 tied for second warmest in the period of instrumental data, behind the record warmth of 2005, in the Goddard Institute for Space Studies (GISS) analysis. 2007 tied 1998, which had leapt a remarkable 0.2°C above the prior record with the help of the "El Niño of the century". The unusual warmth in 2007 is noteworthy because it occurs at a time when solar irradiance is at a minimum and the equatorial Pacific Ocean is in the cool phase of its natural El Niño-La Niña cycle. -- NASA

So what should we expect in the future? Greenhouse gas emissions are only increasing, not decreasing, so we can expect these charts to continue recording an upward trend. There will be dips, and peaks, as climate systems are not linear, but don't expect global warming to subside anytime soon. 2008 is expected to be cooler than 2007 due to the action of our current La Niña phase, but watch out for 2009 and beyond.

Cherry picking ("the act of pointing at individual cases or data that seem to confirm a particular position, while ignoring a significant portion of related cases or data that may contradict that position" -- Wikipedia) single year events in isolation is a simple way to fool the masses, but it is wholly unscientific. Unfortunately, don't expect these denial tactics to end anytime soon. In fact, now get ready for the latest denial statements -- that global warming stopped in January 2007.