Friday, September 08, 2006

Are CO2 Levels at Historical Highs?

I was reading an article in Scientific American that stated that an atmospheric carbon dioxide concentration of 560 parts per million (ppm or µL/L) is widely regarded as capable of triggering severe climate changes. Currently the level is at 380ppm. So, I wondered to myself, how do these values compare to historical levels?

The answer depends on how historical you want to go.

Although contemporary CO2 concentrations were exceeded during earlier geological epochs, present carbon dioxide levels are likely higher now than at any time during the past 20 million years and at the same time lower than at any time in history if we look at time scales longer than 50 million years.

In more recent times, atmospheric CO2 concentration continued to fall after about 60 Myr BP, and there is geochemical evidence that concentrations were <300 µL/L by about 20 Myr BP.
As the graph shows, over the last 500,000 years we are at a high. CO2 levels were 280ppm before the industrial revolution, about the high of the cycles throughout the last 500,000 years. Now we are way beyond that.

But, if you expand your time horizon "a bit" further it appears that our current levels are on the low side.
While these measurements give much less precise estimates of carbon dioxide concentration than ice cores, there is evidence for very high CO2 concentrations (>3,000 µL/L) between 600 and 400 Myr BP and between 200 and 150 Myr BP.
As this graph shows, CO2 levels are much lower (almost ten times lower) than they were when dinosaurs walked the earth 150 million years ago.

I don't know where scientists come up with the fact that 560ppm will cause severe climate change, but it is certainly true that the earth has sustained life before with much higher levels. Some worry that the earth will become like Venus and be completely inhabitable. Seems unlikely given that the dinosaurs and other creatures were able to thrive in the higher levels.

I have written before that we should figure out the best temperature for life on earth and get the earth to that level. But, I overlooked the issue that the rate of temperature change might be more important than the actual average temperature. If the temperature increases gradually it gives species time to adapt while a sudden change doesn't. So, the scientists are probably right to worry about rapidly rising levels of CO2, but I wish we understood more what the impact of higher CO2 levels and temperatures meant for life on earth back in the days of the dinosaurs.

via Wikipedia

7 comments:

al fin said...

The greenhouse impact of CO2 concentration is not linear, but rather logarithmic. That means that the response curve tends to flatten out after reaching certain concentrations. Straight line extrapolations are useless in this case.

Another problem with GCMs is the total neglect of solar variability. Not understanding the impact of solar variation, among other things, leads modelers to overconfidence in their multi-decadal predictions.

mping said...

Al,

Interesting point, I was not aware the logarithmic relationship. You wouldn't happen to know how much temperatures are predicted to change if the carbon dioxide concentration went from 380 to 550 would you?

I too am skeptical about the global climate models. I wonder if they have enough data to reliably predict the future. I had read an economist state that the modeling going on reminded him of economic monetary models of the 70s. They had models of how things were supposed to work based on their historical data, but reality didn't match up well with the predicted values of the models.

But, most of the things that are recommended to stop global warming: reduce usage of oil, natural gas and coal, use more solar and wind power, stop deforestation and start reforestation are things that I think we should do regardless of global warming. So, even if the models are off, I think there will be benefits to implementing the changes.

Anonymous said...

but the warm-blooded animal in this warm time had the sizes of mice and was nocturnal. also the sun nuclear reactor was younger and heated less.
the only solution i found until now against the global warming and the natural destruction is a economical solution.
our economy must follow the exponential growth curve of interest and compound interest. but nature cannot be made to increase like capital, so industrialization has created a threatening problems to the natural earth system.the only solution is fixing our actual economic system errors with economic reform proposed by the economist Silvio Gesell "The natural economic Order". our economic system must get a upgrade to be sustainable for the long run without war and natural destruction. This all lead not only to a balanced coexistent nature it also lead to a real modern society.

Anonymous said...

It is also not always known that higher levels of CO2 causes more luscious plant life. During the time of the dinosaurs, the earth was much greener than what it is now. Perhaps the 10X higher CO2 levels?

Anonymous said...

There is only one practical way to limit co2 emissions. We talk about co2 emissions per person, well multiply that by the number of people and you have the total co2 emissions. The only feasible way is to limit population growth.
Each country needs to manage it's population level. Very few countries have not exceeded their suitable population level.
It is the only way.

Anonymous said...

Anyone who advocates for population control should lead by example.

As far as C02 goes, our planet is a closed system. We cannot introduce anything new to it. So perhaps it is not as simple as reducing C02 levels as the planet (as evidenced by the fossil record) is capable of sustaining itself with higher levels of C02. We need more C02 scubbers perhaps (plants) and that would lead us to the real ecological problem facing our planet, that of deforestation. But saving the rainforests is not fashionable anymore so that obvious solution will be ignored. Better to go buy one of the new plug-in Prius. (Priii? LOL) Feel smug driving your electric car, just doesn’t ask where the electricity comes from.

I would rather plant the 10 trees a month needed to offset my family’s carbon footprint and reduce our consumption of meat to once a week than limit my range and mobility of my vehicles or, I don’t know euthanize one of my kids. It is rather arrogant of us to think we matter all that much that we can upset the balance of nature irrevocably by our actions. Even nuclear war, while devastating would not be the end of life on earth. Hell, from a Darwinian macro-evolutionary standpoint, the radiation may provide for a massive explosion in mutations, giving evolution a kick in the pants thus spurring on countless new forms of life.

Anonymous said...

My wife and I decided the best thing we could do for the planet was not to have children but co2 levels continue to rise. The recent info on ocean acidification shows that our actions can easily upset the balance of nature. With 25% of atmospheric co2 being absorbed by the ocean, rising co2 levels has caused ocean acidity to increase by 30%. Thru our actions, we are altering the basic chemistry of sea water and making it more difficult for plankton and coral (the basis of the ocean food chain) to form. Plankton produces 50% of the oxygen on the planet and plankton levels have decreased by 40%.

When the dinosaurs were alive, most of the oceans were devoid of life. It took 30 million years for life to reestablish itself. The consequences of ocean acidification are catastrophic with devastating effects for humans as well since such a high percentage are dependent on the ocean for their food. I am sure that mankind is not going extinct but the lose of biodiversity to the planet would be phenomenal, not just ocean life but all the animals that are dependent on the ocean for food plus all the species that are currently being driven to extinction by climate change.

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