CO2 and Global Warming

Here are a few graphs that show the connections between CO2, temperature, fossil fuel emissions, and changes in our climate. Certainly, CO2 represent just one of several important greenhouse gases, but it’s easiest to focus on here.

Here’s recent temperature deviations from Brohan etal (2006). Each point is a global average, and the error bars are the coldest/warmest months of each year.


We’ve increased 1C over the last century.

Here are fossil fuel emissions plotted on top of recent CO2 concentrations in the atmosphere (data come from a variety of sources including Marland et al 2008).


Humans increased atmospheric CO2.

The following plot shows the connection between CO2 and temperature over the last 400,000 years, obtained by analyzing ice cores (Petit et al 1999).


When people say there are natural variations to climate, yes, it’s true. It’s also true that humans weren’t responsible for these variations: Essentially, a wiggling Earth/Sun orbit is thought to be the driver. But this driver has nothing to do with the changes over the last 200 years.

Underlying these greenhouse gas concentrations and warming trends are the energy fluxes from the Sun and subsequent pathways through our atmosphere. Here’s a great figure from Kiehl and Trenbreth (1997):


Changing the atmosphere’s chemical composition via our emissions, or even by adding reflective dust in the upper atmosphere, ever so slightly alters the balance at each one of these steps.

Different atmospheric components apply different “forces” to global warming, here summarized in a plot by the IPCC Physical Science report:

forcingCO2 has the greatest forcing, though other chemicals might have a greater per-molecule forcing. Note the total forcing is around 1-2 Watts per square meter, compared with 168 W/m2 solar energy hitting Earth’s surface in the previous plot. That’s about one percent. Don’t let mentions of solar output, like this IPCC plot,


sow doubt about global warming: Yes, solar output varies, but climate scientists know and understand that fact. These solar output variations are less than one-tenth of one percent.

Those changes result in climate change. Furthermore, how a warming Earth changes soil respiration, for example, represents one of many “feedbacks” that makes climate predictions difficult.

And, so, what happens as a result? This plot shows that trees are flowering earlier (Roetzer etal 2000), as much as a month in some places.


Birds are laying their eggs a couple of weeks earlier (Dunn and Winkler 1999; this data might be updated somewhere).


That’s just a short overview of a small part of the science that exists demonstrating global warming. As with everything, there remain unknowns. There’s nothing political about it. It is clear that emissions have warmed Earth, changed climate, and will continue to make changes. End of story. Let’s stop emissions.


Brohan, al. 2006. Uncertainty estimates in regional and global observed temperature changes: A new data set from 1850. J. Geophys. Res. 111:D12106.

Dunn, P.O., and D.W. Winkler. 1999. Climate change has affected the breeding date of tree swallows throughout North America. Proc. Roy. Soc. Lond. B 266: 2487-2490.

Kiehl, J.T.,  and K.E. Trenberth. 1997. Earth’s Annual Global Mean Energy Budget. Bull. Amer. Meteor. Soc. 78: 197-208.

IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt,
M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.

Marland, G., al. 2008. Global CO2 Emissions from Fossil-Fuel Burning, Cement Manufacture, and Gas Flaring: 1751-2005. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory.

Petit, J.R. et al. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399:429-436.

Roetzer, T., M. et al. 2000. Phenology in central Europe: differences and trends of spring phenophases in urban and rural areas. Int. J. Biometeorol. 44:60-66.

5 Responses to “CO2 and Global Warming”

  1. Richard says:

    Specifically, your evidence does not stand up.

    1) Your first chart reveals that temperature anomalies in the 1930′s are almost at the height you graph gives for 2000. Referring to your second chart, we see that the 1930′s temperatures rose without significant emission. In fact, your second chart shows co2 and temperature emissions beginning to soar around 1950. But the first chart actually shows a decline in temperature from about 1950 to 1970. Your first chart shows that temperature only reached 1930 levels about 2000.

    2) Your second chart is suspect. It basically replicates the old hockey stick graph which has been roundly discredited. Ice drilling does not create a closed-end system. First, to measure co2 in ice you need pure ice without water content. The coldest ice we have does contain water into which co2 is soluble. This solubility affects the nature of the gas being measured. The introduction of the vibrations of the drill itself and the use of drilling lubricant (“drilling mud) changes the gas concentration in the ice. This comment is based on the work of Dr. Zbigniew Jaworski, known as an ice core expert.

    3) Your third chart shows temperature every 100,000 year, like clockwork. You identify the earth sun orbit as the driver. Then you say the increase in the last 200 years is not due to this factor. How do you know? You do not present any evidence.

    4) Your fourth and fifth charts do not prove anything harmful is going on. Co2 is a fertilizer and is used to induce flower growth and blooming in greenhouses. The concentrations used are several times the normal concentration in the atmosphere generally. One of the benefits of increased co2 in the atmosphere, together with increased sunshine, is the increased crop growth especially important to nations with hungry people. I do not see the rate of bird-egg laying as being relevant to anything. So what? Your straight-line smoothing is misleading, because your raw data shows no consistent grouping of events that can be plotted. In fact your data shows that egg-laying delay occurred more frequently in the 1980′ than the 90′s. You also present no foundation for the chart and no evidence of what has happened in the last 20 years.

    As the farmer told the motorist who asked for directions, “You can’t get there from here.”

  2. Will says:

    Thank you for your comments.

    I agree, the decrease in the 1940s-1960s is intriguing. Atmospheric pollution in the upper atmosphere can have a “shading effect”. I’ve put that plot together with a histogram of atmospheric nuclear weapons tests here, which puts dust into the upper atmosphere. A potentially interesting connection, but the plot hasn’t been peer-reviewed, so it should be taken with a grain of salt. Also realize that up until the 1950s, our primary energy source was coal (shown here, a much dirtier source of energy than our petroleum/natural gas sources today. How that air pollution affected warming isn’t clear, but all of those sources add fossil carbon, promoting the long-term warming trend.

    The “hockey stick” has been discredited? Please provide the primary reference, I’ll read it and get back to you, posting the data you cite. That’s how science works. For your convenience, the “hockey stick” reference involves a citation to Crowley 2001, available at

    Right, the 100,000 year Milankovitch cycles are quite fascinating. A spectral analysis of these cycles demonstrate that the last 100 years of warming has a different source of variation, however, than those long term cycles. Recent warming is a novel occurrence. I’m not quite sure if your comment here presupposes that warming is taking place (in contradiction to your first two comments), or whether you question the precise mechanism — human or celestial. (I assume it’s of the form: It’s not taking place, but if it is, we’re not to blame.)

    There are many documented life history changes taking place in many organisms, and my plots show some of the earliest reported cases. These data are so commonplace that journals reject them for showing nothing new. It is correct that CO2 concentration affects the growth rates of a variety of species, for example, it can change the carbon to nitrogen ratio of plants, which changes the growth rate of herbivores. However, temperature has a larger effect. Indeed, data exist for ice break-up data on lakes and the average last frost dates, phenomena not subject to CO2 concentrations. The simplest explanation for these phenomena, which science seeks, is a warming climate, shown in the earlier plots.

    Again, thank you for your comments.

  3. Prof. James Barrante says:

    Nice try, but no cigar. There is no scientific evidence supporting the contention that correlations between CO2 and atmospheric temperature and different now from what they have been over the last 400,000 years. First, 200 years is too short a period of time to draw any scientific information about climate change that will hold up to the scientific method. Second, CO2 is not an effective greenhouse gas at a concentration of only 0.04%. And most importantly, Henry’s Law is still operating as it has been since water was a liquid on this planet. The temperature changes before atmospheric CO2 changes, not after. Our oceans have been controlling CO2 in the atmosphere, since the Earth cooled to below the boiling point of water. Atmospheric CO2 has been rising over the past 200 years because our oceans have been warming. A 1 to 2 degree change in global temperature is common. Look at your own graphs. In fact, really look at your own graphs. Within the next 3000 to 10,000 years most of North America should be under a couple of miles of ice.

  4. Will says:

    Thank you for your comments.

    Certainly looking long time horizons, there will be much colder periods ahead. It’s happened in the past. No doubt it will happen in the future. Indeed, the points in that 400K year graph have a resolution of 1500 years, so a many-century averaging underlies the correlation.

    But is that kind of time scale really the one that concerns most people? In my estimation, it’s the next 100 years that should be concern us. Regarding 200 years being too short a time to draw any scientific questions, it certainly depends on the question. Science works on many topics having long time scales: planet formation and death, plate tectonics, oceanic current changes, and so on, yet we have made great strides in recent decades in understanding these phenomena. Human influences on climate and ecosystems will, undoubtedly, have effects lasting decades, centuries, and millennia, and we can make great strides in observing, understanding, and ameliorating those effects. I’m not swayed by the fatalistic outlook that just because Earth’s climate is subject to 100,000 year cycles, there’s no point to changing our ways for the betterment of people 50 or 100 years from now.

    In my humble opinion, the today’s fundamental problem with climate change is that we have a present-day population that’s 40 to 400 (dependent on diet) times greater than 20,000 years ago, and sustaining that high population depends critically on the climate we’ve enjoyed over the last century, and, more importantly, the use of fossil fuels to produce fertilizers and enable mechanized agriculture. I think we have a moral obligation to sustain that population over the next 50 to 100 years (as we work to reduce birth rates). We need to face reality and do what we can today to avoid greater problems tomorrow. As a mere human, I’m humbled, for example, by the impact of invasive species, and what might happen to our agricultural species under climate change. Think about the American Chestnut, for example, nearly wiped out by a pathogen in just a couple of decades. Only now has plant breeding nearly brought this tree back to us. Do we really know, for example, the potential ecological consequences of adding a couple of degrees C to our climate? Will that expose our important crops to new environmental threats? We don’t know, period, but we do know that climate change affects many organisms’ life history through many pathways. There is an obligation to minimize the risks.

  5. michael says:

    >>>Atmospheric CO2 has been rising over the past 200 years because our oceans have been warming.<<<

    Certainly CO2 solubility is less in warmer water, but for the ocean to be the source of increasing atmospheric CO2, what must be happening to dissolved CO2? It would have to be decreasing (ie. leaving the water to enter the atmosphere). What is actually happening to dissolved CO2? It is INCREASING. Therefore, it CANNOT be the source of increasing atmospheric CO2.

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