There was a comment on this WUWT post which I found to be very interesting.
Plants require a certain amount of CO2 to survive. People claim that ice cores taken from Antarctica and Greenland show that CO2 levels during the last ice age dropped to 180ppm. It’s then claimed that a 180 to 280 climb drove us out of the ice age.
The problem is that plants don’t do well at 180. Most just die. Grasses can scrape by, but it’s rough on them. So a period of 100k years of starvation should have had a major hit on grasses and destroyed other plants. Apart from being buried under a whole lot of ice.
Since that didn’t happen it seem reasonable to assume that the CO2 measurements from the ice cores are not accurate.
This is the comment:
Gail Combs says:
…..In past times, during the transition between an ice age and a warm period, atmospheric CO2 concentrations changed by some 100 parts per million (ppm) – from an ice age value of 180 ppm to about 280 ppm during warm periods….
If this was true there would be no trees and certainly nothing like mammoths during the last ice age. At 180 ppm Class 4 plants (grasses) could possibly survive but would not have the “energy” to produce seed. At 200 pm CO2 trees starve http://biblioteca.universia.net/ficha.do?id=912067 (That link of course has since been purged from the internet – SURPRISE – not)
…According to Barnola et al (1987) the level of CO2 in the global atmosphere during many tens of thousands of years spanning 30,000 to 110,000 BP were below 200ppm. If this were true then the growth of C3 plants should be limited at the global scale because their net Photosynthesis is depressed as CO2 concentration in air decreases to less than about 250ubar (less than about 250ppmv)(McKay et al 1991) This would lead to the extinction of C3plant species . This has however not been recorded by paleobotanists (Manum 1991).”http://www.co2web.info/stoten92.pdf
“…Plant photosynthetic activity can reduce the CO2 within the plant canopy to between 200 and 250 ppm… I observed a 50 ppm drop in within a tomato plant canopy just a few minutes after direct sunlight at dawn entered a green house (Harper et al 1979)” Source
Another study on wheat (a grass) in open fields showed the CO2 level 2 meters above the crops was reduced to a near constant 300 ppm during the day but fluctuated during the night. Again indicating a lower threshold of 250 ppm ~ 300 ppm and certainly not indicative of below 180 ppm.
WHEAT: The CO2 concentration at 2 m above the crop was found to be fairly constant during the daylight hours on single days or from day-to-day throughout the growing season ranging from about 310 to 320 p.p.m. Nocturnal values were more variable and were between 10 and 200 p.p.m. higher than the daytime values.
From the people who know and depend on the truth – FARMERS
…Plants use all of the CO2 around their leaves within a few minutes leaving the air around them CO2 deficient, so air circulation is important. As CO2 is a critical component of growth, plants in environments with inadequate CO2 levels of below 200 ppm will generally cease to grow or produce… http://www.thehydroponicsshop.com.au/article_info.php?articles_id=27
….With the advent of home greenhouses and indoor growing under artificial lights and the developments in hydroponics in recent years, the need for CO2 generation has drastically increased. Plants growing in a sealed greenhouse or indoor grow room will often deplete the available CO2 and stop growing. The following graph will show what depletion and enrichment does to plant growth:
GO TO SITE for CO2 vs Plant Growth GRAPH
Below 200 PPM, plants do not have enough CO2 to carry on the photosynthesis process and essentially stop growing. Because 300 PPM is the atmospheric CO content, this amount is chosen as the 100% growth point. You can see from the chart that increased CO can double or more the growth rate on most normal plants. Above 2,000 PPM, CO2 starts to become toxic to plants and above 4,000 PPM it becomes toxic to people….. http://www.hydrofarm.com/articles/co2_enrichment.php
Keith in another WUWT discussion brought up another good point the effect of partial pressure of CO2 at higher elevations on plants.
Speaking of carbon dioxide as plant food there is something else often missing in discussions of CO2 concentration. That is CO2 and its relation to altitude. Humans have trouble breathing near the top of Mount Everest even though the “concentration” of oxygen in parts per million is the same as at sea level. This is because the total density of the air is less so the actual amount of oxygen available per cubic meter is also less. The same holds true for carbon dioxide. Air density at 1000 meters altitude is about ninety percent of its sea level value, and crops grown at that altitude have access to ninety percent of the CO2 at sea level despite the fact that the “concentration” as usually given is the same. Half of the land surface of the earth is about 840 meters above sea level, and the absolute concentration of CO2 there is therefore ninety percent less. http://www.ecowho.com/blogs/120/CO2_global_levels_rising%2C_is_this_a_problem%3F/-b33b2
Now when will Engelbeen come to valiantly defend this very important pillar of CAGW? After all low CO2 is the KEY to CAGW.
Dr. Jaworowski tried to do the study to determine the accuracy of the Ice Core CO2 data but the funding was turned down because it was feared his study would “Disprove” the CO2 readings from the ice cores and we couldn’t have that now could we???
Another comment from Gail:
Gail Combs says:
Aside from the plants during the Ice Age showing the CO2 reading are way off there is another elephant in the room.
It is called Water Vapor.
95% of the green house effect is caused by WATER not CO2. It is up to 4% where as CO2 is a puny 0.036% That is why water is left out of the IPCC reports. (Another lie by omission) http://www.geocraft.com/WVFossils/greenhouse_data.html
Next what did the last ice age to to the water content of the atmosphere???
Glacial Climate and Sea Level
The North American and European ice sheets of the last glaciation began forming after a prolonged cold stage with increased precipitation (mostly snow in this case) took place. Once the ice sheets began forming, the cold landscape altered typical weather patterns by creating their own air masses. The new weather patterns that developed reinforced the initial weather that created them, plunging the various areas into a cold glacial period.
The warmer portions of the globe also experienced a change in climate due to glaciation in that most of them became cooler but drier. For example rainforest cover in West Africa was reduced and replaced by tropical grasslands because of a lack of rain.
At the same time, most of the world’s deserts expanded as they became drier….
So there goes the change of 100 ppm in CO2 having any effect because it would be completely swamped by the water vapor changes! Not to mention the effect of the Milankovich cycles that would directly effect those changes in the amount of water vapor.
The influence of these cycles on insolation (INcident SOLar radiATION) at different latitudes has been calculated by Berger (1991), and Laskar (1993). Below is Berger’s solution for 65 degrees north latitude from the present to 1 million years ago. In the Northern Hemisphere, peak summer insolation occurred about 9,000 years ago when the last of the large ice sheets melted. Since that time Northern Hemisphere summers have seen less solar radiation. http://deschutes.gso.uri.edu/~rutherfo/milankovitch.html
Of course we KNOW the sun has nothing to do with our climate because climate scientists tell us that is so. /sarc>
So as usual these [self-snip] scientists are busy chasing grant money with the get out of peer review CO2 card and not doing real science.
It is completely wrong to assume that CO2 measurements from ice cores have anything to do with absolute values. They can show trends and highs and lows, but they are NOT quantitative in any way. Jaworowski, the leading expert has stated that there is 30–50% losses of CO2 during the traumatic process of core extraction. If you back calculate the losses, you end up with CO2 concentrations the same or higher than now.It is only the IPCC that likes to pretend that ice core data, clearly indirect data, is quantitative—it is NOT!