Figure 1. 420,000 years of CO2, CH4, Oxygen isotope ratios, insolation, and Temperature from the Vostok ice core. (Reference)
P.J. Rovero, Meteorologist and Oceanographer
Last updated: February 27, 2010
Global climate change is a fact. The problem is that the climate has always been changing, and not always due to human activity.
The study of past climates, particularly those before historical instrumented records, is called paleoclimatology. Paleoclimatologists use a number of proxies to substitute for the lack of actual temperature measurements. These include:
All of the proxy data get less detailed as we go back in time. This means that very recent data will show year to year variations, while older data may show "running average" readings over decades, centuries, millenia, and millions of years. And as the data get older, the uncertainties and error bars get a bit bigger. So the curves on the graphs get much smoother and less accurate with the older data. In other cases, we just don't have really old data from some of the proxies. For example, ice core data go back only 800K years, with a hope to extend the record back a bit more than a million years.
Additional forcing of global climate changes comes from the precession of the earth's poles, the eccentricity and obliquity of the earth's orbit around the sun. In fact, the 100 Kyr, 41 Kyr, and 26 Kyr spectral components of these predictions are found in ice cores and sea floor sediment data. There are, however, significant phase shifts between the times of maximum and minimum insolation and the climate shifts.
Some of the most compelling data comes from the analysis of Antarctic and Greenland ice cores. The core series going back farthest in time are the Vostok (450 Kyr) and European Project for Ice Coring in Antarctica (EPICA , 800 Kyr). And what do these cores show? As illustrated in Figure 1 below, there have been a series of four long, cold glacial periods interrupted by relatively short interglacial periods over the last 420 Kyr. The EPICA core goes on to show four more glaciations in the 400 Kyr previous period. The Vostok and EPICA cores agree quite well over the common period of record.
Figure 1. 420,000 years of CO2, CH4, Oxygen isotope ratios, insolation, and Temperature from the Vostok ice core. (Reference)
We live in the most recent interglacial period -- the same one in which agriculture developed, along with the rest of "recorded" human history. What the ice core record shows is increasing CO2, CH4, and temperature for the last 18,000 years. The Industrial Revolution accounts for only the last 1% of this time period -- a figurative "boil on the butt" of an existing, non-anthropogenic global warming trend.
As more than one observer has noted, Fourier analysis of this time series might lead one to believe we are getting ready start another period of glaciation. It is unclear what triggers the periodic rapid warmings and coolings -- it is not only predicted orbital cycle changes in insolation, or changes in CO2/CH4 levels. Other parameters that may contribute include dust (from soil erosion and volcanic eruptions, which have been observed in the ice core and ocean sediment records) and small changes in the amount or character of solar or cosmic radiation. The consensus view appears to be "nobody knows for sure, but it probably wasn't human beings".
A number of investigators have also noted that temperature fluctuations appear to lead the changes in CO2 and CH4 by 500 to 1000 years, when exactly the opposite might be expected by the most popular global warming theories.
Robert A. Rohde has prepared the following graph showing a number of different Holocene (last 12,000 years) temperature reconstructions. Note the inset for the last 2,000 years. Note that there is significant variability in the different proxy reconstructions, and that the present time is not the warmest period.
Figure 2. 12,000 years of proxy temperature reconstructions.
We are in a period of global warming that started 18,000 years ago. Human beings have contributed to detectable climate change on the micro-, local and regional scales through changes in land use and population (and energy consumption) concentration. The urban heat islands are a good example. Human beings may have contributed to changes in global climate through changes in land use and industrial emissions of CO2, CH4, and other "greenhouse" gases. The certainty and magnitude of those potential anthropogenic changes is a matter of current scientific research and political dispute.
In view of the paleoclimatology record, I believe that some scientists have gone too far propagating a crisis mentality and supporting sweeping political "solutions" to a problem that may not even exist. Those scientist who fudge the data (and won't release it), and who have tried to exclude scientists with contradictory data from publication have certainly gone too far. Scientists who switch from the science to political advocacy risk damaging science.
In view of the uncertainties in the paleoclimatology record, I do not believe that sweeping political "solutions", particularly those that concentrate power in governments, are needed at this time. It is appropriate to promote energy conservation and renewable sources of energy. That can be done without the hype, global treaties, global targets, and so-called "cap and trade" tax increases.
If you believe in anthropogenic global warming, take direct action to reduce your energy and greenhouse gas (carbon, methane, CFC, etc.) footprints. For example, don't take two trips to Scandinavia in Air Force One (one for the Nobel Peace Prize, one for the "climate summit") when one trip will do. Stop opposing the efforts of others to build non-carbon-emitting solar, wind and nuclear energy projects. Lead, or get out of the way.
Reduce your energy use at home:
If you are not willing to do these yourself, stop trying to tax, legislate, or otherwise get other people to do them
