Since the little ice age around 1800 (and arguably earlier) the earth has been warming at a linear rate (linear regression line) that is unaffected by increases in atmospheric CO2 which reflects human activity. A simple reality that global warming alarmists do not accept.
Unfortunately for the global warming alarmists, the correlation between CO2 and temperature that they claim is the basis for warming (presumably since the little ice age) is at best weak and recent studies suggest it could even be upside down with CO2 increasing after temperature has risen. Since 1998 they hung their hat on Mann's infamous hockey stick theory but had to quickly backtrack when it was debunked a few years ago. To make things a bit murkier, scientists have complained that the published temperature data is unreliable, reflecting a number of factors including improper siting of measurement stations, urban heat effect, choice of dates, differences in warming and cooling depending on geographical location vs. claims of "global" warming, etc. Other theoretical attempts to identify evidence of man's effect have failed, including an inability to explain a cooling of the atmosphere with increased altitude (i.e., theoretically anthropogenic driven warming should result in an increase in temperature with altitude) which was documented a few years ago by the government's climate change program. The absence of this anthropogenic "fingerprint" is a major nail in the alarmist's coffin. Putting it all together leads many to conclude that human activities play a minor role in climate change.
However, one can reasonably ask how minor is the role of human forcings on climate change. The latest IPCC report stated that most of the observed increased warming is very likely due to an increase in anthropogenic greenhouse gases in the atmosphere. Of course, this does not explain the increase since the little ice age and other "small" problems. More importantly the IPCC does not define what they mean by most (i.e., 50%, 70%, etc.) because they cannot. Not surprisingly, the media picked up on "most" and the naive followed along without questioning.
How does one determine how much human forcings contribute to climate change by increasing the amount of minor greenhouse gases such as CO2 in the atmosphere? One way to get a handle on the fraction of the warming due to human forcings is to subtract the linear trend in temperature since the little ice age from temperature measurements. Given the temperature data, whatever the result of this calculation it certainly will not show that the IPCC's "most" comment is justified. Secondly, there are climate models. Unfortunately for alarmists current climate models are unverified and produce results all over the "map." It is amusing to watch modelers scramble as each new piece of historical data emerges that differs from what the models matched in the past and then have to tweak variables until they match the most recent historical data. However, the more they tweak the models the more uncertain their forecasts become which is characteristic of over optimization. To their credit, the IPCC acknowledged this in their latest report.
In qualitative terms, there are numerous reasons for the failure of the models. Very importantly the models do not take into account solar activity although it has been shown for decades to be highly correlated with the earth's temperature. Duke physicists estimate that since 1900 the sun has contributed about 50% of the observed temperature increase which apparently the alarmists consider to be a drop in the bucket. When one adds negative feedback effects there is not much room left for greenhouse gases in toto (about 2% of the atmosphere) or greenhouse gases related to human activities (particularly CO2 which is about .08% of the atmosphere) to have much effect. Beyond that the models do not (1) adequately take into account the effect of clouds (arguably related to solar activity), (2) address the negative feedback of water vapor (about 95% of greenhouse gases), (3) explain geographical differences in temperature trends, (4) explain the correlation between ocean oscillations and temperature, (5) explain dramatic weather patterns such as monsoons or other regional climate changes, (6) etc. At least part of the models' problem was revealed by a former NASA physicist who showed that the models assumed an infinitely thick atmosphere. When this was changed to match the actual thickness of the atmosphere and a negative feedback term added the temperature increase is less than previous forecasts which in the past have overstated reality.
When all is said and done we are left with unverified climate models which are essential to determining by the scientific method (i.e., observe, hypothesize, predict, test) the degree to which human activities affect climate. We are also left with a variety of measurements which show that the current warming is consistent with the trend in temperature since at least 1800 (long before any claim of significant human forcings). Despite this reality, we still have to contend with those who worship at the church of global warming and agitate for "insurance" and other political actions to counter a perceived threat that they have no evidence exists. According to some scientists the next cooling phase is coming down the track sooner rather than later at which point there will undoubtedly be alarmists who demand that we burn more fossil fuel in order to elevate greenhouse gases and thereby keep warm (recall when they raised their voices in the late 1970s). One has to admire folks who "boldly go where no one has gone before" as they take on the power of the sun and other natural phenomena.
Edited by colion, 17 March 2008 - 09:16 AM.
