Wednesday, September 19, 2007

Trenberth on "Some climate change fallacies"

Climate Feedback: The recent Asian Pacific Economic Cooperation (APEC) summit has brought further attention to climate change and what, if anything, to do about it. In spite of the IPCC findings that global warming is “unequivocal”, doubt remains in some quarters about the reality of climate change and the human cause. Issues are continually raised that have no basis, as highlighted by the recent Commentary from Syun-Ichi Akasofu in the Wall Street Journal.

Akasofu immediately starts out on the wrong foot by claiming there are two sides, those of believers and non-believers, but it is not a matter of belief, it is a matter of scientific facts! He further fails to understand the nature of the IPCC process and the extensive reviews in which all comments are addressed rigorously as the report is developed over three years. Contrary to the claim, there is no assumption by IPCC that recent warming was due to the increased greenhouse effect from increasing human produced carbon dioxide. Rather, climate models that run with and without the human-induced changes in atmospheric composition demonstrate that human warming has emerged from natural climate variability since about 1970.

Over the past 500,000 years or so, temperatures, carbon dioxide and methane have gone up and down more or less in tandem through the major ice ages and interglacial periods, as shown in ice cores. As detailed in a Real Climate blog post on this topic, in the absence of human intervention, these changes happen over time, but not at the rate at which CO2 is currently increasing in the atmosphere. Scientists know that carbon dioxide and methane changes follow rather than cause these changes in temperature between glacial periods, but they also know that these changes in greenhouse gases amplify a relatively weak forcing to help drive temperature change. To suggest otherwise, as Akasofu does, is misleading at best.

Akasofu then trots out the mistaken view that the “hockey stick” curve of temperatures over the past 1000 years showing an upward bend at the end has been discredited. In fact, it has been reinforced in the latest IPCC report, although it is given less emphasis as it is now backed up and confirmed by evidence from multiple independent studies.

He further claims that natural climate variations have been forgotten and attributes recent warming to the “rebounding effect from the little ice age”, but fails to realize that natural climate variability also has a cause. While it is true that we do not have the measurements to show what was happening in the ocean during this time, for instance, we have good reason to believe that natural internal variability played a role. To the extent that the "Little Ice Age" and "Medieval Warm Period" can be meaningfully defined, there has been much work showing that the main variations can be explained in terms of the response of the climate system to natural variability in solar and volcanic events that would have influenced surface temperature. And warm periods in the past, such as the warming in the Greenland region in the mid-twentieth century, were not global in contrast to recent warming, which is.

Climate models are not perfect, but they are useful tools for quantifying the effects of various climate processes and drivers of climate change. Akasofu decries the confused state of climatology, but it is he who is really confused, and his article only serves to confuse the general public. It is sad that a once distinguished newspaper published such misleading half-truths without verifying them. ...Kevin Trenberth

1 comment:

Angee said...

People have more and more informations about the climate now and the IPCC report is considered more of a bedtime story than a scientific study. The loss of the IPCC report was, among others, the fact that they failed to define climate.

If they would have seen climated in relation with the oceans (as known, climate is the continuation of oceans by other means), their report would be totally different, in the way that it would have been objective.