Pieter Tans

on .

(Head of the "Carbon Cycle Greenhouse Gases Group, NOAA's Earth System Research Laboratory" - http://www.esrl.noaa.gov/gmd/)
Climate change is becoming the most important challenge for humanity in the near future. Understanding the driving factors of global warming is a starting (and key) point in this challenge. One of these factors is the measure of CO2 concentration in the atmosphere. According to the record of CO2 and temperature preserved in ice sheets in Antarctica and Greenland, there is a clear correlation between CO2 concentration in the atmosphere and air temperature (the higher the concentration, the higher air temperature will be). On May 9th 2013 CO2 concentration at the Mauna Loa Observatory (the site chosen by Charles D. Keeling, the scientist who started the studies on  the proportion of carbon dioxide in the atmosphere) reached 400 parts per million (ppm). During the last glaciations CO2 concentration in the atmosphere was 180 ppm; in 1800 (pre-industrial era) CO2 concentration was 280 ppm; now it has reached 400 ppm. A concentration of 500 ppm is considered by some scientists as an irreversible point, by which Earth will reach a new hotter equilibrium. What does all this mean? Is there something to worry about? What can we do to reverse this process? Pieter Tans, Head of the Carbon Cycle Greenhouse Gases Group, answered to these and other questions.
Pieter Tans: Pieter Tans is the Head of the Carbon Cycle Greenhouse Gases Group in the Global Monitoring Division of NOAA's Earth System Research Laboratory in Boulder, Colorado. For his work in expanding our understanding of the global carbon cycle and raising awareness for climate change, Pieter Tans, Ph.D., was awarded the Roger Revelle Medal* at the 2010 fall meeting of the American Geophysical Union in San Francisco. Among his many achievements, Tans is best known for discovering that the carbon dioxide released by burning fossil fuels that is not accounted for in the ocean or the atmosphere is stored in land ecosystems in the Northern Hemisphere.

* Established in 1991, the Revelle Medal is named in honor of Roger Revelle, who made substantial contributions to the awareness of global change. Revelle served as an AGU (American Geophisical Union) section president for the Ocean Sciences section (1956–1959). The Revelle Medal is awarded not more than once annually to an individual “for outstanding contributions in atmospheric sciences, atmosphere-ocean coupling, atmosphere-land coupling, biogeochemical cycles, climate, or related aspects of the Earth system.” Edward N. Lorenz was the first recipient of the Revelle Medal. http://sites.agu.org/
The interview was realized in July 2013 and published in September 2013 - (Original interview in English)
Subject: CO2 concentration in the atmosphere - meaning, dynamics and effetcs on climate change
1. Question: The NOAA ESRL Carbon Cycle Greenhouse Gases group (CCGG) analyzes the concentration in the atmosphere of the carbon-cycle gases and other greenhouse gases* in four baseline observatories**. Why are such analyses being made in these observatories?

These observatories were started in the early 1970s primarily for the purpose of keeping track of the increase of greenhouse gases in the atmosphere. Air samples were also taken regularly in flasks at about 20 sites world wide and sent to Boulder, Colorado, for analysis. Soon it became evident that we could do more than merely keeping track of changes in the atmosphere. We could see systematic spatial patterns in the atmosphere resulting from emissions and removals of the greenhouse gases.  For example, the annual average concentration of greenhouse gases is higher in the northern hemisphere than in the southern hemisphere. For CO2 the difference has increased steadily over the decades as the rate of CO2 production from the burning of coal, oil, and natural gas has increased. Emissions from any place on earth get spread through the entire atmosphere in about one year’s time. The observed spatial patterns of greenhouse gases allow us to quantify emissions and removals when we use atmospheric transport models derived from the weather forecast.

*  carbon dioxide - CO2 -, methane - CH4 -, nitrous oxide - N2O -, carbon monoxide – CO -.
** Barrow- Alaska - and Mauna Loa – Hawaii – in the Northern hemisphere; American Samoa - Tutuila Island, South Pacific – and South Pole - Antarctic plateau -.

2. Question
: On May 9th 2013, daily mean concentration of carbon dioxide in the atmosphere of Mauna Loa, Hawaii, surpassed 400 parts per million (ppm) for the first time since measurements began in 1958. Could you explain in poor words what does mean “ppm” and what are the consequences of having such a concentration of CO2 in the atmosphere? If we stopped CO2 emissions now, for how long we would have 400 ppm of CO2 in the atmosphere?

“400 Parts per million (ppm)” means that in every million molecules of (dry) air there are 400 CO2 molecules. We call that the (dry) air mole fraction of CO2. We measure CO2 and other greenhouse gases that way because the mole fraction does not change when the air pressure or temperature changes (and the air expands or contracts), or when water vapor is added or removed. Only emissions or removals of greenhouse gases can change their mole fraction in dry air.  At 400 ppm CO2 is substantially higher now than it has been in the last several million years. Furthermore, CO2 cannot be removed from the atmosphere + ocean + terrestrial biosphere system by natural means on a time scale of many thousands of years. If we stopped emissions now, the excess CO2 would continue to be re-distributed between the atmosphere and oceans, but it will not disappear. The effect of enhanced greenhouse gases on the heat balance of the Earth (and other planets) is also known from well understood physics and chemistry. The implication is that climate change is already programmed in for a very long time. 

3. Question
: In the last glaciations CO2 concentration in the atmosphere was 180 ppm, then it increased to 280 ppm. Since 1800 CO2 concentration at the Mauna Loa center has increased by about 116 ppm. Do you think this increase is only the result of human activities? What are the main driving factors of such an increase (carbon fuelled industries, deforestation, traditional agricultural methods, positive feedbacks – e.g permafrost melting)? Will the emergence of some populous countries, like China and India, further accelerate this process?

We can conclusively prove that the observed “CO2 increase is entirely man-made”. It results mostly from fossil fuel burning, and secondarily from deforestation or land use change in general. The latter was the largest factor until the mid-20th century, but fossil fuel burning is the overwhelming driver today. Other attempted explanations, such as a volcanic origin or ocean out-gassing, are contradicted by the observations. Our observations also show that, at least at this point, permafrost melting is not (yet?) a significant contributor.

4. Question
: In particular, what do you think about the impact the current agricultural systems (based on one-crop methods and on a massive use of fossil fuels) has on the process of CO2 accumulation in the atmosphere?

In terms of a direct impact on the carbon cycle agricultural practices at this time are very much secondary to fossil fuel burning. However, the production of fertilizer as well as pesticides, herbicides, etc., and food storage are (fossil) fuel intensive. They do contribute in this way to emissions of CO2 and are typically counted as industrial emissions, while intensive agriculture is a major contributor to (inadvertent) emissions of the two other major greenhouse gases CH4 and N2O.  

5. Question
: As said by James Lovelock in his “The Revenge of Gaia”, according to some studies, reaching 500 CO2 ppm means reaching a point of non-return: it would bring the collapse of oceanic life (primarily algae – one of the main absorbers of CO2); the temperature would have a sudden strong increase and the Earth would reach a new equilibrium, hotter and less liveable for human beings. By projecting the current trend, when do you think such a point will be reached?

I do not know when such “tipping points” are reached. All CO2 emissions are irreversible on the time scale of human civilizations, and there is a lot of time for slow climate feedbacks to take effect. We are now experiencing only the beginning of man-made climate change. The ocean’s heat content has not been able to keep up with the rapid atmospheric change, ice sheets may take centuries to shrink, permafrost melting may take a century. Methane hydrates in continental margins may become unstable over hundreds of years. Climate feedbacks and sea level rise are already programmed in, but we cannot quantitatively predict them well until we have enough observations to test our evolving model predictions. We will learn about climate change as we go…   

6. Question
: What can we do to reverse the process? Would it be better acting in reducing the demand for energy (e.g. Transition towns movement) or in changing the supply of energy (from traditional sources to renewable or nuclear ones)? There are some ideas to put in place technological systems to reduce global warming (reflecting the sun's rays back into space, making clouds whiter and seeding the ocean with minerals to absorb more CO2). What do you think would be the right approach to face the problem?

It is abundantly clear that “we have to bring emissions of CO2 down to zero as soon as we can.” We actually have most of the means to do so. That would also bring to a halt the ongoing acidification of the oceans (CO2 is an acid), threatening the ocean food chain if it continues. The first on my list of priorities is greatly improved energy efficiency and conservation. It creates meaningful jobs, and increases the effectiveness of all the other things we might want to do. Sweden was able to cut its per capita CO2 emissions in half in about 20 years after the oil price shocks of the 1970s. Second on my list is stopping all direct subsidies to fossil fuel consumption and production. The International Monetary Fund recently estimated that globally these subsidies amount to US$480 billion per year, conservatively counted. Instead, that money could be invested in our future by bringing wind and solar energy to the scale that is required. Third, bring population growth under control primarily by bringing equal rights and education to all women, which has proven to be very effective, and fundamentally very desirable. Fourth, hold on to nuclear power for electricity production. In fact, resurrect the development of more inherently safe nuclear reactor designs and proliferation-proof nuclear fuel cycles, such as thorium.
I am not favorably impressed with most climate engineering proposals that I have heard about. What we are now experiencing with CO2 is a form of inadvertent climate and ecosystem engineering. I don’t think we understand the climate system, and the Earth system, well enough to justify further tinkering, and countries might not even agree on objectives.

7. Question: What do you think are (and will be) the worst consequences of climate change?
8. Question: How do you imagine the world by 100 years?
I do not want to think too much about questions 7 and 8.  The world could become a very unpleasant place.  I prefer to think about all of the positive changes we have the power to make, for our own sake and for future generations.
9. Question: Finally, if you could send “a message to humans”, what would you suggest to do in order to preserve themselves and our Planet in the long period? In particular, what are the main 5 actions to put in place in order to avoid a further warming of our planet.
I answered this more or less in question 6. The bottom line is that climate change is one, out of many, manifestations that “our economic system cannot continue to grow forever”, as most economists, politicians, and the public effectively appear to believe.  We need to figure out how to create a socio-economic system that is static, or even one that is capable of shrinking the throughput of materials, while providing meaningful employment and opportunities to the majority of people. What comes to mind are education, and taking care of each other and of the Earth’s environment, our only home. Traditional production will be done by robots, whether we like it or not.