Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings Lectures by Greg Podgorski, Utah State University Methane, Plants and Climate

Slide 1Lectures by Greg Podgorski, Utah State University
Methane, Plants and Climate Change
Scientific American
Concept Review
What do you do when you find something that contradicts the textbooks?
Frank Keppler and Thomas Röckmann faced this question when they found a new source of methane – living plants.
Their answer?
Repeat your experiments to be sure of your results, then tell the world through a publication reviewed by other scientists.
Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings
Concept Review
Methane (CH4) is best known as “natural gas.”
Methane is an important greenhouse gas.
Pound-for-pound, methane is 23 times more effective than carbon dioxide in trapping heat.
Human activities have tripled the levels of atmospheric methane over the past 150 years.
Roughly 600 million metric tons of methane are produced annually.
Knowing all sources of methane is essential if its levels are to be controlled.
Concept Review
The finding that plants produce methane flew in the face of conventional wisdom.
By 2001, the Intergovernmental Panel on Climate Change (IPCC) believed all major sources of methane had been identified.
Plants were not on the list.
Concept Review
Prior to Keppler and Röckmann’s discovery, the major known sources of methane were:
Anaerobic bacteria (including those that live in the digestive systems of cows and other ruminants)
Forest and savannah fires
Burning of fossil fuels
But based on these sources, fluctuations in methane levels before humans started burning fossil fuel (during the Industrial Revolution) could not be explained.
Concept Review
The discovery that living plants produce methane was accidental.
Keppler and Röckmann were interested in chloromethane, a gas that destroys ozone.
They knew that decaying plant material produced chloromethane, and wondered if it also made methane.
They found that tiny amounts of methane were produced by dried plant material.
Concept Review
What about living plants?
They found that living plants produced 10 to 100 times more methane than dried plant material.
The amount of methane produced by each plant is small, but the cumulative amount is huge.
Keppler and Röckmann estimated that plants produce 60 – 240 million metric tons of methane annually.
Concept Review
According to these figures, plants could be responsible for 10% to 40% of global methane emissions.
Keppler and Röckmann knew that current views about methane production would make it difficult for many scientists to accept these figures.
Strengthening their case, two independent lines of evidence were discovered that supported links between plants, methane, and climate change.
Concept Review
Satellite observations showed huge clouds of methane over tropical forests that couldn’t be explained by existing models.
A reanalysis of previous data showed massive releases of methane from tropical savannah, which is explained by plant methane production.
Even so, many scientists remain skeptical of the magnitude of methane production by plants and are repeating Keppler and Röckmann’s studies.
Concept Review
Understanding that plants produce methane explains previous puzzling observations.
Methane levels were known to vary in step with the Earth’s temperatures.
Concept Review
The plant-methane link also means that global warming will drive further increases in temperature.
Warmer Earth
More plants
More methane
Concept Review
The media ran headlines like “Global Warming – Blame the Forests.”
Plants have been emitting methane for hundreds of millions of years.
They have not caused the sharp increase in methane output seen since the Industrial Revolution.
Concept Review
Plants are an essential source of the oxygen on which life as we know it depends.
The major cause of global warming is not plants – it’s the burning of fossil fuels.
Concept Review
Plant production of methane raises a serious concern.
Which is greater – the benefit of carbon sequestration from planting forests, or the harm caused by the methane those forests give off?
Calculations show that the benefit of planting more trees is greater.
Testing Your Comprehension
a) chlorofluorocarbon.
b) chloromethane.
c) natural gas
c) a major contributor to acid rain.
d) taken up by plants for use in photosynthesis.
The discovery that living plants produce methane happened by accident when scientists were studying:
a) the sources of an ozone-destroying gas.
b) how plants produce oxygen during photosynthesis.
c) how plants absorb carbon dioxide.
d) the ecology of savannah ecosystems.
The discovery that living plants produce methane happened by accident when scientists were studying:
a) the sources of an ozone-destroying gas.
Knowing that plants produce methane solves the long-standing mystery of:
a) the winter ozone hole over the Antarctic.
b) global warming.
c) why plant biomass increased during interglacial periods.
d) the coupling between atmospheric methane and changes in Earth’s temperature.
Knowing that plants produce methane solves the long-standing mystery of:
d) the coupling between atmospheric methane and changes in Earth’s temperature.
a) a spread of plants across every land area.
b) the destruction of all large life forms.
c) ever-increasing global temperatures.
d) an equilibrium between global temperature, plant life, and methane levels.
Warmer Earth
More plants
More methane
c) ever-increasing global temperatures.
Biology and Society
When the media misinterprets scientific findings, it is the fault of scientists, who should have explained the meaning of their work more clearly.
Disagree Agree
Thinking About Science
Calculations show that in terms of global warming, the positive effect of carbon sequestration by reforestation outweighs the negative effect of methane production by plants. In addition to knowing the amount of carbon taken up by growing trees, what else would you need to know to make these calculations? (Hint: more than one answer may be correct.)
a) The amount of methane produced by growing trees.
b) The relative heat-trapping properties of carbon dioxide and methane.
c) The growth rate of trees in different global regions.
d) The current rate of world-wide temperature increase.
Thinking About Science
Calculations show that in terms of global warming, the positive effect of carbon sequestration by reforestation outweighs the negative effect of methane production by plants. In addition to knowing the amount of carbon taken up by growing trees, what else would you need to know to make these calculations? (Hint: more than one answer may be correct.)
a) The amount of methane produced by growing trees.
b) The relative heat-trapping properties of carbon dioxide and methane.
Interpreting Charts and Graphs
What conclusion can be drawn from comparison of the two graphs?
There has been no change in the amount of biomass burned.
The amount of methane produced from wetlands has increased.
c) There are fewer termites in modern times.
d) There was more burning of biomass in preindustrial times.
Interpreting Charts and Graphs
What conclusion can be drawn from comparison of the two graphs?

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Copyright © 2009 Pearson Education, Inc. publishing as Benjamin Cummings Lectures by Greg Podgorski, Utah State University Methane, Plants and Climate