Posted by
James Nichols on Friday, September 28, 2007 12:02:08 AM
The argument that CO2 levels were higher in the ancient past is not relevant to today's climate discussion -- the sun's energy output was much lower (in the few percent range but quite considerable in terms of climate) during the Jurassic, but then with the higher CO2 levels the temperatures were higher as well. In the Precambrian (before 550M yrs ago) it appears that the earth was quite cold, probably seesawing between glaciers reaching the oceans at the equator and milder conditions as CO2 levels fluctuated. Only with increasing solar output did the earth finally remain thawed out.
It is quite incorrect to say that CO2 is not a significant greenhouse gas, the absorption of light and infrared energy by gases has been accurately measured, I'm just a dumb engineer but I could do a calculation in a few weeks time to determine the temperature of an inert ball at the earths distance from the sun with the reflectance and atmosphere of the earth --- that determination is just not in doubt in any way.
However the earth is not an inert ball -- it has mass, it has weather, and it has life. The interaction and play of these elements of the earth make predicting the climate/ temperature very near impossible. One can say with certainty that the earth will in the future be warmer with a higher CO2 level in the atmosphere but by how much? There are competing effects, warmer oceans may increase cloud cover thus reducing the final temperature rise due to the higher reflectance of sunlight, reduced snow cover will increase the temperature due to the lessened reflectance, forest fires may become more frequent further increasing CO2 levels, and methane hydrates deep in the northern oceans may decompose releasing the much stronger greenhouse gas, methane; accelerating a temperature rise.
Climate has changed in the past without mankind's interference and will continue to do so. Take for example the Medieval Warm Period that allowed the Vikings to colonize Greenland and plant crops in what is now permafrost only to be followed a few hundred years later by what is referred to as the Little Ice Age that ended the Vikings northern colonization. 10,000 years ago the Sahara was nearly as dry as it is now, 8,000 years ago it was green and inhabited -- now it is dry again -- peoples have been displaced by climate change, glaciers ebbed and waned -- inhabitants were forced out by advancing ice sheets, then returned again. We are now in the early years of what will be a prolonged interglacial period. Civilization rose and flourished in a unique postglacial period with abundant water in lakes and rivers from melting glaciers that we will not see again for a very long time. The seas will continue to rise no matter what we do as we pass into this interglacial period.
Unfortunately those scientists with agendas will use events beyond our and their control in an attempt to gain power and advantage over their fellow citizens and any real message that they may have for us will be lost in their rhetoric.