Recently I wrote a large number of subject-specific articles for a two-volume reference work entitled Climate Change: In Context. Somehow it fell into the hands of a climate-change “skeptic” for review. This person snarked to the publisher:
Most interesting is that the atmosphere reached a peak in 1998 and has been cooling since 2002. I'd be interested in seeing one of your writers response to that.
My pleasure; I’ll respond in full in a moment. But I’d like to note first the rhetorical, gestural kinship between creationism and climate-change denial. Both schools of thought claim that a small, intrepid minority of truly independent-minded thinkers sees an elephant in the living room (e.g., the unreality of climate change, the lack of any evidence whatever for evolution) that most of the world’s practicing scientists dishonestly refuse to see or are mysteriously unable to see. To bolster this vision of a beleaguered prophetic minority they rely heavily on the careful framing of certain facts in isolation from the patterns around them. These factoids, when properly isolated, colored, framed, spun, and cross-linked to other, similarly processed factoids, seem to make a convincing case -- especially to well-meaning people with little or no knowledge of science -- against the mainstream scientific view. This omission of context is a powerful tool for causing confusion and creating the appearance of mass scientific delusion or controversy over basic ideas where none exists.
In this case, the facts or factoids being isolated from their surrounding pattern are global average surface temperatures for the last decade or so.
I have two points to make. The first is general. The second responds to the specific point raised about cooler years.
(1) The reality of human-caused global warming is affirmed by every single US government science agency and by every major non-governmental science organizations in the world. For example, NASA states that “recent observations of warming support the theory that greenhouse gases are warming the world.”  NASA attributes these gases’ increase to human agency.  The US Climate Change Science Program states that for North America -- which has experienced less warming than the global average -- “seven of the warmest ten years for annual surface temperatures from 1951 to 2006 have occurred between 1997 and 2006.”  The US National Oceanic and Atmospheric Administration states that air temperatures at the Earth’s surface, as well as at higher altitudes, have been increasing and notes that “seven of the eight warmest years on record have occurred since 2001 and the 10 warmest years have all occurred since 1995.”  Here are the data from the Intergovernmental Panel on Climate Change :
There are critics of this overwhelming scientific consensus, and some of these critics even have scientific credentials. However, their claims that global climate change is either not real or is not primarily human-caused are almost never defended in the peer-reviewed scientific literature.  They are expressed in blogs, media interviews, newspaper articles, speeches, petitions, testimony to Congress, and non-peer-reviewed books -- in a word, outside the scientific process. Creationists, of course, operate in exactly the same fringe zone.
In writing a climate textbook it would therefore be the height of scholarly irresponsibility, akin to advancing Creationism in a biology textbook, to adopt or give serious consideration to any view of climate change other than the only view articulated extensively in the recent scientific literature: namely, that global climate change is real and human-caused. To even pretend that there is substantial scientific debate over the basic reality and human-caused nature of global warming would be to essentially lie to readers.
(2) “Most interesting is that the atmosphere reached a peak in 1998 and has been cooling since 2002.”
I reproduce again the IPCC’s figure:
Note that climate does not warm uniformly, in a smoothly climbing ramp or curve. It bobbles as it rises. Runs of cooling years alternate with runs of warming years. The process is a noisy one. The occurrence of a run of cooling years, either recently or in the near future, is almost inevitable. To point to such a run as evidence against global warming is fallacious, exactly as it would be to point to a cold snap in April as evidence that summer was not coming. Those who argue so misunderstand -- one can hardly help but feel, when the claim is coming from a scientist, willfully misunderstand -- the obvious character of the instrumental record.
In particular, any cooling that has occurred in recent years has done so against the background of dramatic overall warming (unprecedented in at least the last 1300 years) seen in the figure. Taking 2 steps back when you have already gone 30 steps ahead leaves you 28 steps ahead.
The last decade of data can be spun as “a peak in 1998 followed by cooling.” But what the data actually show, in the historical context, is a spike in 1998 followed by a string of some of the hottest years on record. NASA states that the 2008 meteorological year “was the ninth warmest year in the period of instrumental measurements, which extends back to 1880. The nine warmest years all occur within the eleven-year period 1998-2008.” 
The 1998 spike is clearly visible in the above graph (the lone gray dot floating above the black 5-year averaged line). Both that spike and the “cooling trend” of the years since are noisy squiggles on a very long-standing rising trend. Similar squiggles are superimposed over the entire instrumental record. And it is the long-term trend that matters. Nothing else matters. Nobody is arguing in the real, peer-reviewed scientific literature that anything else matters. All claims to the contrary are pseudoscience.
Our book drew solely upon the most reliable scientific sources, such as the US government science agencies and the peer-reviewed literature (e.g., Science and Nature). It assumed throughout the only responsible educational account of global warming possible, given the state of the science: global warming is occurring, it is significant in magnitude, and it is human-caused. Recent weather has nothing to do with these conclusions because it is too short-term.
 Naomi Oreskes, “The Scientific Consensus on Climate Change,” Science, 3 December 2004, p. 1686. I will send a PDF of this article to any inquirer.